Ain Shams Engineering Journal

Chemical and Physical Properties of Poly(Lactic) Acid (PLA) Modified Bitumen--Manuscript Draft--

Manuscript Number: ASEJ-D-19-00656R2

Article Type: Full Length Article

Section/Category: Civil Engineering

Keywords: Chemical interaction; Compatibility; Dispersity; Modified bitumen; Physicalproperties; Poly(Lactic) Acid.

Corresponding Author: Nur Izzi Md Yusoff, PhDUniversiti Kebangsaan MalaysiaBangi, MALAYSIA

First Author: Nashriq Jailani, MSc

Order of Authors: Nashriq Jailani, MSc

Ahmad Nazrul Hakimi Ibrahim, PhD

Abdur Rahim, PhD

Ahmad Kamil Arshad, PhD

Norhidayah Abdul Hassan, PhD

Nur Izzi Md Yusoff, PhD

Abstract: This study investigates the feasibility and effect of poly(lactic) acid (PLA) on bitumenmodification. The chemical and physical properties were evaluated for the modifiedbitumen produced with varying percentages of PLA ranging from 3 to 9%. Severaltestings such as the nuclear magnetic resonance (NMR), Fourier Transform InfraredSpectroscopy (FTIR), Gel permeation chromatography (GPC), penetration, softeningand ductility, and thermal storage stability were evaluated. The results show thatchemical interaction exists between PLA and bitumen. The GPC analysis indicateshigh compatibility of the bitumen with the PLA modifier. Moreover, the results indicatedthat the addition of PLA increased the consistency of modified bitumen. The storagestability and segregation of phases were positively affected in the PLA modifiedbitumen. The PLA and base bitumen interact at physical and chemical levels whichresults in enhancement of performance of modified bitumen to produce a high-qualitybinding material for pavement construction.

Response to Reviewers: List of comments and response

Point 1: More suitable title should be selected for the article.Response 1: The authors has changed the manuscript title to “Chemical and PhysicalProperties of Poly (Lactic) Acid Modified Bitumen”.

Point 2: The abstract should state briefly the purpose of the research, the principalresults and major conclusions. An abstract is often presented separately from thearticle, so it must be able to stand alone.Response 2: The abstract in the revised manuscript has been rewritten and restructurebased on suggested outline by Reviewer 4.

Point 3: It is suggested to present the structure of the article at the end of theintroduction.Response 3: The structure of article was presented at the end of the introduction.

Point 4: The major defect of this study is the debate or Argument is not clear stated inthe introduction session. Hence, the contribution is weak in this manuscript. I wouldsuggest the author to enhance your theoretical discussion and arrives your debate orargument.Response 4: The authors has revised and restructured the whole introduction sectionin the revised manuscript. The revised introduction provided a well discuss related thetheoretical and finding of the previous related works. In addition, the limitation of the

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previous works is well derived and identified as the main reason this study wasconducted.

Point 5: The necessity and innovation of the article should be presented to theintroduction.Response 5: Based on limitation of the previous works, this study was conducted tobridge the gap of knowledge. The necessity of this study is presented in theintroduction and the innovation of this study is described as well in the revisedmanuscript.

Point 6: More suitable title should be presented for the figure 11 instead of "Softeningpoint value of PLA-modified bitumen".Response 6: The title of Figure 11 and Figure 12 in the revised manuscript has beenrevised.

Point 7: It is suggested to compare the results of the present research with somesimilar studies which is done before.Response 7: The findings of this study was compared to the results of the relatedprevious studies. The discussion of this can be seen in Section 3 (Results) and Section4 (Discussion).

Point 8: A flowchart should be added to the article to show the research methodology.Response 8: The flow chart was added in Figure 1 to summarize the flow of researchprotocol.

Point 9: Following, you will find some new related references which should be added toliterature review:Saedi & Oruc. The Effects of Nano Bentonite and Fatty Arbocel on Improving theBehavior of Warm Mixture Asphalt against Moisture Damage and Rutting;Shihab et al. Effects of Temperature in Different Initial Duration Time for Soft ClayStabilized by Fly Ash Based Geopolymer;Nhabih et al. Study a Structural Behavior of Eccentrically Loaded GFRP ReinforcedColumns Made of Geopolymer Concrete.Response 9: The relevant information from these suggested studies have been used toenhance the sentence and discussion in the revised manuscript. In addition, thesesuggested studies were added in the revised manuscript.

Point 10: Page 11: the following paragraph is unclear, so please reorganize that:"Lower indexes were observed for the area under the band of C-O with C-C for theunwashed (11.0 to 7.0%) and washed (10.6 to 5.1%) samples. On the other hand, anincreasing index pattern was observed for both the C=O bond with C-C (unwashed=4.7 to 17.9%; washed=12.1 to 16.9%) and the C=O with C=C (unwashed=1.0 to 7.3%;washed=9.0 to 18.9%).".Response 10: This sentence has been revised.

Point 11: Much more explanations and interpretations must be added for the Results,which are not enough.Response 11: The authors has extended the explanations and interpretations of thefindings in this study. See Result and Discussion section.

Point 12: It is suggested to add articles entitled "Iqbal et al. Improving the AgingResistance of Asphalt by Addition of Polyethylene and Sulphur", "Kadhim & Al-Mutairee. An Experimental Study on Behavior of Sustainable Rubberized ConcreteMixes" and "Trang et al. The Study of Dynamics Heterogeneity in SiO2 Liquid" to theliterature review.Response 12: The relevant information from these suggested studies have been usedto enhance the sentence and discussion in the revised manuscript. In addition, thesesuggested studies were added in the revised manuscript.

Point 13: Please make sure your conclusions' section underscore the scientific valueadded of your paper, and/or the applicability of your findings/results, as indicatedpreviously. Please revise your conclusion part into more details. Basically, you shouldenhance your contributions, limitations, underscore the scientific value added of yourpaper, and/or the applicability of your findings/results and future study in this session.

Response 13: The authors has rewritten and restructure the conclusion of this study. Inaddition, the suggestion for future research also listed in the same section.

Point 14: "Notation" should be added to the article.Response 14: The “notation” was added in the figure and text in the revisedmanuscript.

Point 15: DOI of the references must be added (you can use "https://crossref.org/").Response 15: The DOI number was added for all references in the revised manuscript.Thank you for your suggestion of using "https://crossref.org/". See Reference section.

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JABATAN KEJURUTERAAN AWAM, FAKULTI KEJURUTERAAN DAN ALAM BINA, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan

Telefon: +603-8921 6447 Faksimili: +603-8911 8344 E-mel: izzi@ukm.edu.my Laman Web: http://www.eng.ukm.my

Fakulti Kejuruteraan dan Alam Bina Faculty of Engineering and Built Environment

Chief-in-Editor Ain Shams Engineering Journal 26th December 2020 Dear Prof, SUBMISSION OF A REVISED MANUSCRIPT – R2 FOR POSSIBLE PUBLICATION IN AIN SHAMS ENGINEERING JOURNAL Hereby I have attached a revised manuscript entitled “Effects of Chemical and Physical Properties of Poly(Lactic) Acid (PLA) Modified Bitumen” co-authored by Nashriq Jailani, Ahmad Nazrul Hakimi Ibrahim, Abdur Rahim, Ahmad Kamil Arshard, Norhidayah Abdul Hassan and Nur Izzi Md Yusoff for a possible publication in the Ain Shams Engineering Journal. Please do not hesitate to get in touch with me if you have any questions and I look forward to hearing from you very soon. Thank you very much indeed.

Kind regards, Assoc Prof. Ir. Dr. Nur Izzi Md. Yusoff Dept. of Civil Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia 43600 UKM Bangi Selangor, Malaysia Tel: +603-8921 6447 (office), +6019-289 1221 (mobile) Fax: + 603-8921 6147 Email: izzi@ukm.edu.my, izzi.alkutani@gmail.com

Cover Letter

CORRECTION REPORT

TITLE:

Chemical and Physical Properties of Poly (Lactic) Acid Modified Bitumen

(REF: ASEJ-D-19-00656R1)

We are very pleased to have been given the opportunity to revise our manuscript, which is entitled,

“Chemical and Physical Properties of Poly (Lactic) Acid Modified Bitumen” for the Ain Shams

Engineering Journal. We have carefully considered those offered by a reviewer. Here, we explain how

we have revised the paper based on those comments and recommendations. We would like to extend our

gratitude all parties for taking the time and making the effort to provide such insightful guidance.

The response to all comments from Reviewer 4 is shown in the list of comments and response

and attached revised manuscript.

In conclusion, we appreciate all the insightful comments. We have done our best to make the

recommended amendments. Thank you for the time and effort to help us improve the writing

of this paper. We hope that you will approve the revised version of this paper.

Thank you.

Detailed Response to Reviewers

List of comments and response

Point 1: More suitable title should be selected for the article.

Response 1: The authors has changed the manuscript title to “Chemical and Physical Properties

of Poly (Lactic) Acid Modified Bitumen”.

Point 2: The abstract should state briefly the purpose of the research, the principal results and

major conclusions. An abstract is often presented separately from the article, so it must be able

to stand alone.

Response 2: The abstract in the revised manuscript has been rewritten and restructure based

on suggested outline by Reviewer 4.

Point 3: It is suggested to present the structure of the article at the end of the introduction.

Response 3: The structure of article was presented at the end of the introduction.

Point 4: The major defect of this study is the debate or Argument is not clear stated in the

introduction session. Hence, the contribution is weak in this manuscript. I would suggest the

author to enhance your theoretical discussion and arrives your debate or argument.

Response 4: The authors has revised and restructured the whole introduction section in the

revised manuscript. The revised introduction provided a well discuss related the theoretical and

finding of the previous related works. In addition, the limitation of the previous works is well

derived and identified as the main reason this study was conducted.

Point 5: The necessity and innovation of the article should be presented to the introduction.

Response 5: Based on limitation of the previous works, this study was conducted to bridge the

gap of knowledge. The necessity of this study is presented in the introduction and the

innovation of this study is described as well in the revised manuscript.

Point 6: More suitable title should be presented for the figure 11 instead of "Softening point

value of PLA-modified bitumen".

Response 6: The title of Figure 11 and Figure 12 in the revised manuscript has been revised.

Point 7: It is suggested to compare the results of the present research with some similar studies

which is done before.

Response 7: The findings of this study was compared to the results of the related previous

studies. The discussion of this can be seen in Section 3 (Results) and Section 4 (Discussion).

Point 8: A flowchart should be added to the article to show the research methodology.

Response 8: The flow chart was added in Figure 1 to summarize the flow of research protocol.

Point 9: Following, you will find some new related references which should be added to

literature review:

Saedi & Oruc. The Effects of Nano Bentonite and Fatty Arbocel on Improving the Behavior of

Warm Mixture Asphalt against Moisture Damage and Rutting;

Shihab et al. Effects of Temperature in Different Initial Duration Time for Soft Clay Stabilized

by Fly Ash Based Geopolymer;

Nhabih et al. Study a Structural Behavior of Eccentrically Loaded GFRP Reinforced Columns

Made of Geopolymer Concrete.

Response 9: The relevant information from these suggested studies have been used to enhance

the sentence and discussion in the revised manuscript. In addition, these suggested studies were

added in the revised manuscript.

Point 10: Page 11: the following paragraph is unclear, so please reorganize that:

"Lower indexes were observed for the area under the band of C-O with C-C for the unwashed

(11.0 to 7.0%) and washed (10.6 to 5.1%) samples. On the other hand, an increasing index

pattern was observed for both the C=O bond with C-C (unwashed= 4.7 to 17.9%; washed=12.1

to 16.9%) and the C=O with C=C (unwashed=1.0 to 7.3%; washed=9.0 to 18.9%).".

Response 10: This sentence has been revised.

Point 11: Much more explanations and interpretations must be added for the Results, which

are not enough.

Response 11: The authors has extended the explanations and interpretations of the findings in

this study. See Result and Discussion section.

Point 12: It is suggested to add articles entitled "Iqbal et al. Improving the Aging Resistance

of Asphalt by Addition of Polyethylene and Sulphur", "Kadhim & Al-Mutairee. An

Experimental Study on Behavior of Sustainable Rubberized Concrete Mixes" and "Trang et al.

The Study of Dynamics Heterogeneity in SiO2 Liquid" to the literature review.

Response 12: The relevant information from these suggested studies have been used to

enhance the sentence and discussion in the revised manuscript. In addition, these suggested

studies were added in the revised manuscript.

Point 13: Please make sure your conclusions' section underscore the scientific value added of

your paper, and/or the applicability of your findings/results, as indicated previously. Please

revise your conclusion part into more details. Basically, you should enhance your contributions,

limitations, underscore the scientific value added of your paper, and/or the applicability of your

findings/results and future study in this session.

Response 13: The authors has rewritten and restructure the conclusion of this study. In

addition, the suggestion for future research also listed in the same section.

Point 14: "Notation" should be added to the article.

Response 14: The “notation” was added in the figure and text in the revised manuscript.

Point 15: DOI of the references must be added (you can use "https://crossref.org/").

Response 15: The DOI number was added for all references in the revised manuscript. Thank

you for your suggestion of using "https://crossref.org/". See Reference section.

Chemical and Physical Properties of Poly (Lactic) Acid Modified Bitumen

Nashriq Jailani1, Ahmad Nazrul Hakimi Ibrahim2, Abdur Rahim3, Ahmad Kamil Arshad4,

Norhidayah Abdul Hassan5 and Nur Izzi Md. Yusoff6*

1PhD Student, Dept. of Civil Engineering, Faculty of Engineering and Built Environment,

Universiti Kebangsaan Malaysia, Selangor, Malaysia

Email: nashriqjailani@yahoo.com

2PhD Student, Dept. of Civil Engineering, Faculty of Engineering and Built Environment,

Universiti Kebangsaan Malaysia, Selangor, Malaysia

Email: ahmadnazrulhakimi@gmail.com

3Senior Lecturer (Dr.), Dept. of Transportation Engineering and Management, University of

Engineering and Technology, Lahore, Pakistan

Email: rahim@uet.edu.pk

4Prof. (Ir. Dr.), Institute for Infrastructure Engineering and Sustainable Management,

Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia

Email: drahmadkamil@uitm.edu.my

5Senior Lecturer (Dr.), School of Civil Engineering, Universiti Teknologi Malaysia, Johor,

Malaysia

Email: hnorhidayah@utm.my

6Associate Prof. (Ir. Dr.), Dept. of Civil Engineering, Faculty of Engineering and Built

Environment, Universiti Kebangsaan Malaysia, Selangor, Malaysia

Email: izzi@ukm.edu.my

*Corresponding author: izzi@ukm.edu.my

Title Page (with AU credentials)

Chemical and Physical Properties of Poly (Lactic) Acid Modified Bitumen 1

Abstract 3

This study investigates the feasibility and effect of poly(lactic) acid (PLA) on bitumen 5

modification. The chemical and physical properties were evaluated for the modified bitumen 6

produced with varying percentages of PLA ranging from 3 to 9%. Several testings such as the 7

nuclear magnetic resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), Gel 8

permeation chromatography (GPC), penetration, softening and ductility, and thermal storage 9

stability were evaluated. The results show that chemical interaction exists between PLA and 10

bitumen. The GPC analysis indicates high compatibility of the bitumen with the PLA modifier. 11

Moreover, the results indicated that the addition of PLA increased the consistency of modified 12

bitumen. The storage stability and segregation of phases were positively affected in the PLA 13

modified bitumen. The PLA and base bitumen interact at physical and chemical levels which 14

results in enhancement of performance of modified bitumen to produce a high-quality binding 15

material for pavement construction. 16

Keywords: Chemical interaction; Compatibility; Dispersity; Modified bitumen; Physical 18

properties; Poly(Lactic) Acid 19

1. Introduction 21

Bitumen is produced by refining crude oil through a series of distillation processes and it is 23

composed of heavy hydrocarbons, which are classified into saturates, aromatics, resins and 24

asphaltenes (Günay & Ahmedzade 2020). It is used in various engineering applications such 25

as highway and airfield pavement due to its physical and rheological characteristics as well as 26

impermeability and adhesive properties (Farias et al., 2016; Mohammadiroudbari et al., 2016). 27

However, being a viscoelastic material, bitumen is easily affected by seasonal temperature and 28

rain as well as loading factors including increasing traffic volumes and continuous heavy loads 29

(Ibrahim et al. 2016; 2017; Iqbal et al. 2020). The viscoelastic properties of bitumen are time 30

and temperature dependant. This effect changes in its physical properties, which are reflected 31

in the mechanical properties of asphalt mixtures. Therefore, bitumen should be sufficiently stiff 32

to resist rutting at high temperatures and soft at low temperatures to prevent the occurrence of 33

thermal cracking (Lesueur, 2009; Saedi & Oruc 2020). 34

Manuscript text (without AU credentials)

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The performance bitumen is, traditionally, enhanced with different types of modifiers 36

including; nanomaterial (Omar et al., 2018; Yusoff et al., 2019), geopolymer (Ali et al., 2017; 37

Ibrahim et al., 2016; Rosyidi et al. 2020; Shihab et al. 2018), waste materials such as glass and 38

plastic (Zakaria et al., 2018), and rubber (Al Mansoob et al., 2017). The previous studies 39

indicate that the addition of modifier improves the performance of the binder in terms of 40

elasticity and stiffness, and also reduces the permanent deformation of the pavement resulting 41

from environmental effects and repetitive traffic loading (Braseileiro et al., 2014; Giavarini et 42

al., 1996; Panda & Mazumdar, 1999). However, amongst the different types of bitumen 43

modifiers, the polymers are the frequently used as modifiers and have demonstrated to be good 44

modifying agents in the production of high-performance binder (Brasileiro et al., 2019; Polacco 45

et al., 2005; Padhan & Gupta, 2018; Sengoz et al., 2009; Zhu et al., 2014). 46

The evidence for performance enhancement with polymers is demonstrated by Jiang et 48

al. (2020) and Laukkanen et al. (2018). According to the studies, the modification of bitumen 49

with SBS enhances the engineering properties of the bitumen for reduced temperature 50

dependence, increased elasticity, as well as an enhanced performance at low and high service 51

temperature. This is due to the excellent mechanical properties of SBS such as high fatigue 52

resistance, elastic recovery and high resistance at extreme temperatures (Airey, 2004; Chen et 53

al. 2007; Schaur et al. 2017). Another thermoplastic modifier that has been widely used for 54

bitumen modification is crumb rubber (CR). According to Poovaneshvaran et al. (2020), Wang 55

et al. (2020a, 2020b, 2020c) and Yao et al. (2018) CR can modify the physical and mechanical 56

properties of bitumen to produce improved resistance to fatigue and thermal cracking, ageing, 57

and rutting. Loderer et al. (2018) reported that, unlike SBS-modified bitumen, CR-modified 58

bitumen has a high resistance to rutting and low-temperature cracking. Moreover, other studies 59

on bitumen modification with natural rubber show enhancement of physical and rheological 60

properties of the modified bitumen (Al-Mansob et al. 2014) and improvement in resistance to 61

shear stress (Poovaneshvaran et al. 2020). Furthermore, the modification of bitumen with 62

polymers has demonstrated to improve the binder properties, for instance, enhanced stiffness 63

at high temperatures, cracking resistance at low temperatures, moisture resistance, and longer 64

fatigue life (Alata et al., 2013; Gardiner et al., 1995; Al Mansoob et al., 2017). The promising 65

potential of using polymers such as rubber and geopolymer is not limited to the bituminous 66

materials only. Numerous evidences were found related to the promising effect of using these 67

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polymers in other applications including as structural and concrete materials (Nhabih et al. 68

2020; Kadhim & Al-Mutairee 2020). 69

The findings of the previous studies related to the polymer modified bitumen are 71

promising and establish the applicability of polymer in bitumen. Within this scope, this 72

research explores the potential of PLA as a modifier. PLA is a bio-based green thermoplastic 73

polyester which can be derived from renewable resources such as sugarcane or cornstarch 74

(Auras et al., 2004; Rasal et al., 2010). Furthermore, PLA is an attractive substitute for 75

conventional polymers due to its excellent biocompatibility, high tensile strength, and high 76

modulus. The simplicity of the PLA structure with esters as the repeating unit and carboxyl 77

group as the end chain can explain the chemical reaction that occurs between PLA and bitumen. 78

The pavement engineering field, traditionally, has remained less focused on the 80

chemical reaction occurring between the polymers and bitumen. Since the past several years, 81

the major concern in literature is enhancing the stability and compatibility of bitumen-polymer 82

blends and optimizing the formulation of the blends (Wang et al. 2020). Most reported works 83

on the utilization of polymers as a modifier focus on describing the physical dispersion of 84

polymers in bitumen while ignoring the chemical reaction that occurs in the blend (Yusoff et 85

al. 2014; Rosyidi et al. 2020). 86

In view of the limitations of previous works, this study aims to investigate the chemical 88

and physical performance of modified bitumen with a new bitumen modifier known as 89

poly(lactic) acid (PLA). This research examines the chemical interaction occurring between 90

the PLA and the base bitumen by using multiple spectroscopic techniques. The relationship of 91

the interactions is then confirmed using the sequential dissolution approach, where a reaction 92

mechanism between PLA and bitumen is also proposed. The PLA-bitumen compatibility and 93

the dispersion of PLA in bitumen are also discussed. The current study will be useful to 94

understand the behaviour and properties of PLA in bitumen modification for its potential 95

utilization in pavement engineering. The remainder of this paper is structured as follows. 96

Section 2 describes the materials, blending and testing protocol. Section 3 presents the results 97

and discussion of the outcome in this study. The paper ends with conclusion and 98

recommendations for future research in Section 4. 99

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2. Material and Methods 102

2.1. Materials 104

Poly(lactic) acid (PLA) in pellet form with a melt flow index (MFI) of 20 g/10 min (190 106

°C/2.16 kg) and a density of 1.24 g/cm3 was purchased from Shenzhen Bright China Industrial 107

Co, while the chloroform was obtained from Merck Pvt Ltd, Selangor, Malaysia. The filter 108

paper (Whatman, 150mm, Catalog Number 1001-150) was purchased from a local supplier, 109

and the 60/70 penetration grade bitumen was supplied by a refinery in Port Klang, Malaysia. 110

The physical properties of the 60/70 penetration grade bitumen used in this study are presented 111

in Table 1. 112

Table 1: Physical properties of 60/70 penetration grade bitumen 114

Parameter Standard Unit Specification

Penetration at 25°C ASTM D5 mm/10 60/70

Softening point ASTM D36 °C 49/56

Ductility at 25°C ASTM D113 cm 100 min

Loss of heating ASTM D6 wt. % 0.2 max

Drop in penetration after heating ASTM D5-D6 % 20 max

2.2. Preparation of bitumen blends 116

Aluminum cans (500 cm3) were filled with 200 g of 60/70 penetration grade bitumen and put 118

in a 150 °C oven until they are ready for use. The PLA was dissolved in an appropriate volume 119

of chloroform to obtain a final concentration of 3, 5, 7 and 9 wt. % by base bitumen (250g). 120

The semi-liquid PLA was gradually added (2 mL/min) to the base bitumen at 180 ± 2 °C and 121

a high-shear mixer to blend at 1000 ± 10 rpm for two hours to obtain a homogenous mixture. 122

After this step, the mixture was aliquoted into different cans for subsequent physical and 123

chemical testing. The experimental process of the development of PLA modified bitumen is 124

presented in Figure 1. 125

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Figure 1: Research methodology 142

2.3. Characterization of reactive polymer with bitumen 144

Proton (1H)-nuclear magnetic resonance (NMR) spectra was used to study the structural 146

distribution of PLA and their interaction with the bitumen. The analysis was carried out using 147

the Brucker Advance III HD 400MHz 1-Dimensional NMR spectroscopy with 148

tetramethylsilane (TMS) as the internal standard. Each sample was dissolved in deuterated 149

chloroform (CDCl3) to a final concentration of 10% w/v and the run time was 10 minutes. 150

Fourier-Transform Infrared spectroscopy (FT-IR) was carried out to determine the functional 151

groups and the chemical bonds in the PLA-modified bitumen. All samples were tested in 152

triplicate using the Perkin Elmer Spectrum 400-FT-IR spectrometer. 153

The compatibility of PLA with base bitumen was determined by analyzing the 155

asphaltenes using sequential dissolution via staged extraction approach. The 100 mg samples 156

of bitumen and modified bitumen with 3, 5, 7 and 9% PLA, were washed three times with 10 157

mL of chloroform. Each layer was then filtered with using a filter paper. The residue (in the 158

form of asphaltenes) retained on the filter paper was weighed and compared with the control 159

bitumen. Next, the extracted asphaltenes from the third wash of each sample were recovered 160

and characterized using FT-IR spectroscopy. 161

Gel permeation chromatography (GPC) was employed to analyze the dispersity of PLA 163

in the base bitumen. Dispersity was determined based on molar mass and molar-mass 164

Materials selection and

characterisation

Blending process

Chemical characterization

of PLA modified bitumen

Physical characterization

of PLA modified bitumen

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distribution of the polymer obtained from GPC (Waters 1515) equipped with differential 165

refractive index (RI 2410) and ultraviolet (UV 2487) detectors. The molar masses were 166

separated using Waters Styragel columns in a series with the molar mass ranging from 100-167

500 000 gmol-1. The samples were dissolved in chloroform and analyzed using tetrahydrofuran 168

(THF) as the eluent at a flow rate of 1.0 mL/min (30 °C) for 40 minutes. 169

2.4. Characterization of PLA-modified bitumen 171

The physical characterization of PLA-modified bitumen includes performing the penetration 173

test at a fixed temperature (25 °C) according to ASTM D5 while the softening point was 174

measured with ring and ball approach as per ASTM D36-06 standard. The stability test was 175

carried out by placing the bitumen in an aluminum-covered tube with a diameter of 3.5 cm and 176

a height of 30 cm in a 180 °C oven for three days. The samples were then cooled at ambient 177

temperature and then cut into three sections. The upper and lower sections of each sample were 178

subjected to softening temperature test. The degree of homogeneity of the mixture is indicated 179

by differences in softening temperature between the two sections, where a smaller difference 180

indicates high compatibility of the PLA with bitumen. The ductility test was carried out 181

according to ASTM D113 standard at 25 °C. 182

3. Results and Discussion 184

3.1. Characterization of PLA-bitumen reaction 186

3.1.1. 1-Dimensional Nucleus Magnetic Resonance Proton (1H 1D-NMR) analysis 188

In order to demonstrate the interaction between PLA and bitumen, a representative 1H NMR 190

spectrums and the assigned signals of the control and the bitumen modified with varying 191

percentages of PLA (Figure 2-4). The results in Figure 2 show that there are multiple signals 192

from the chemical shift from 0.8 to 3.5 ppm. The signals were assigned as two parts, the part 193

‘a’ ranges from 0.8 to 1.4 ppm and represents the signals of the aliphatic proton from alkanes. 194

The ‘b’ ranges from 1.5 to 3.5 ppm and represents the protons from alkenes, alkynes or aliphatic 195

with carbonyl such as ketone, aldehyde, ester and carboxyl group. The chemical structure for 196

poly(lactic) acid is shown in Figure 3, where two signals have been detected. The doublet peak 197

absorbed at a chemical shift from 1.58 to 1.60 ppm (labelled c) indicates a proton from methyl 198

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

group (-CH3), and the quartet peak at 5.15-5.20 ppm (labelled d) indicates a proton from the 199

ester side chain (-OCH(CH3)-) of the repeating unit of PLA. Figure 4 shows the stacked NMR 200

of the bitumen modified with 3, 5, 7 and 9% PLA. The four detected signals (a, b, c and d) 201

indicate the occurrence of a chemical interaction between the PLA and the bitumen. The 202

increase in the intensity of the doublet and quartet (peaks c and d) corresponds with the high 203

percentage of PLA in the samples. A comparison with the control bitumen shows the 204

suppression of the signals in the ‘b’ region (Figure 4B) of the PLA-modified bitumen. 205

Figure 2: 1H-NMR spectrum of control bitumen. 208

Nashriq_bitumen + Rh-WMA.001.001.1r.esp

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

Chemical Shift (ppm)

Nashriq_bitumen + Rh-WMA.001.001.1r.esp

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

d Inte

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 3: 1H-NMR spectrum of PLA 210

Nashriq_PLA only.001.001.1r.esp

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5

d Inte

2.35 2.30 2.25 2.20 2.15 2.10 2.05 2.00 1.95 1.90 1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50 1.45 1.40 1.35 1.30 1.25 1.20 1.15

d Inte

5.65 5.60 5.55 5.50 5.45 5.40 5.35 5.30 5.25 5.20 5.15 5.10 5.05 5.00 4.95 4.90 4.85 4.80

d Inte

d 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 4: (A) 1H-NMR spectrum of the bitumen modified with 3, 5, 7 and 9% PLA. (B) 214

Zoom 1H-NMR spectrum between 0.5 to 3.0 ppm of the bitumen modified with 3, 5, 7 and 215

9% PLA 216

3.1.2. Fourier-Transform Infrared (FT-IR) analysis 218

Figure 5 shows a comparison of the FT-IR spectrum of the control bitumen, PLA and the 220

bitumen modified with 3, 5, 7 and 9% PLA. The spectrum shows that the bitumen modified 221

with different percentages of PLA have similar overlapping profiles. A comparison of the 222

spectrum for samples modified with PLA with control bitumen and PLA shows an almost 223

similar profile except for the additional bands at 1098 cm-1 (region i) and 1749 cm-1 (region ii) 224

in the modified bitumen. This indicates the simultaneous presence of the carbon-oxygen (C-O) 225

and carbonyl (C=O) functional groups. A comparison with the PLA spectrum shows a 226

decreased transmittance percentage in the PLA-modified bitumen in region iii (3600-3650 cm-227

1) for the band representing the hydroxyl group (OH). 228

Nashriq_3% PLA.001.001.1r.esp

8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

d Inte

3% PLA

5% PLA

7% PLA

9% PLA

Bitumen

(A) (B) c

Nashriq_3% PLA.001.001.1r.esp

8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

d Inte

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 5: FT-IR spectrum of the control bitumen, PLA and bitumen modified with 3, 5, 7 230

and 9% PLA 231

The compatibility of PLA with bitumen was investigated using sequential dissolution 233

technique via the staged extraction method. The asphaltenes from each sample (the third wash) 234

were extracted and sent for FT-IR analysis to determine their carbonyl index. Figure 6 shows 235

the percentage of asphaltenes for bitumen modified with 3, 5, 7 and 9% PLA. The results are 236

comparable with the percentage of the control bitumen (~14.4%), except for higher asphaltenes 237

content observed in the bitumen modified with 9% PLA (18.1%). Based on the FT-IR 238

spectrum, the carbonyl index (CI) was determined by calculating the area under the carbonyl 239

band absorbed at wavelength 1695 cm-1 and the saturated C-C band at 1455 cm-1 (Eq. 1). The 240

same asphaltenes residue shows that the carbonyl index of the bitumen modified with 3, 5 and 241

7% PLA are slightly higher (~16.3%) than that of the control bitumen (14.5%). Similar to the 242

asphaltenes content, bitumen modified with 9% PLA has a high carbonyl index of 19.7% 243

(Figure 6). 244

CI = x 100 (1) 246

5001000150020002500300035004000

wavenumbers (cm-1)

Bitumen control

3, 5, 7 and 9% PLA

1749.985 cm-1

1098.9 cm-1

3600- 3650 cm-1

area of carbonyl at 1695 cm-1

Region i Region ii Region iii

area of saturated C-C at 1455 cm-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 6: Compatibility and sequential dissolution of different percentages of PLA and 249

bitumen 250

The FT-IR spectrum presented in Figure 5 and the sequential dissolution technique 252

were used as a basis for further investigation of the correlation between the additional C-O 253

band at 1098 cm-1 (region i) and C=O band at 1749 cm-1 (region ii) in the PLA-modified 254

bitumen. The spectrum in Figure 5 which were PLA-modified bitumen was labelled as 255

unwashed (UW) and the PLA-modified bitumen that underwent sequential dissolution notated 256

as washed samples sequential dissolution (WSD). The results were compared to understand the 257

interaction between the PLA and the bitumen. Figure 7 shows the percentage index of C-O 258

bond (region i) while Figure 8 shows the result of C=O (region ii) divided with the area of (A) 259

unsaturated C=C at 1650 cm-1 and (B) saturated C-C at 1455 cm-1. The index pattern of the C-260

O bond is observed to be different from that of C=O when divided with the unsaturated and 261

saturated carbon-carbon interaction. Figure 7 indicates that the UW showed a simultaneous 262

increase from control bitumen in the index of C-O and C=O with C=C from 11.0 to 26.3% and 263

4.7 to 17.9% respectively and C=O with C-C index from 1.0 to 7.3%. While a decreasing 264

pattern of UW sample for C-O bond with C-C index from 11.0 to 7.0% observed. On the other 265

hand, for WSD samples, the result did not show any significant difference in the index of C-O 266

with C=C (~11.1%) except for the 9% PLA (12.7%). Together with UW samples, WSD also 267

showed a decreasing index pattern of C-O bond with C-C from 10.6 to 5.1%. However, an 268

increasing indexes pattern showed for WSD samples of C=O with C=C and C-C each from 269

12.1 to 16.9% and 9.0 to 18.9% respectively. 270

13.8 14.4 14.7 14.5

14.5016.03 16.23 16.42

bitumen control 3% PLA 5% PLA 7% PLA 9% PLA

)asphaltenes

Carbonyl Index

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 7: Comparison of washed and unwashed indexes of C-O bond at 1749 cm-1 (region i) 273

with (A) C=C, and (B) C-C bonds using FT-IR analysis 274

18.520.4

11.0 11.1 11.2 11.112.7

bitumen control 3% 5% 7% 9%

unwashed washed

11.0 10.0 9.0 8.0 7.0

10.6 9.78.1

6.55.1

unwashed washed

9.911.4

12.113.4

14.6 15.416.9

unwashed washed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 8: Comparison of washed and unwashed indexes of carbonyl at 1749 cm-1 (region ii) 279

with (A) C=C, and (B) C-C bonds using FT-IR analysis 280

3.1.3. Gel Permeation Chromatography (GPC) analysis 282

The molar mass and molar-mass distribution or dispersity of PLA throughout the bitumen were 284

examined using GPC. Figure 9 is the stacked GPC chromatograms of the control bitumen and 285

the PLA-modified bitumen, while Figure 10 shows the zoom chromatograms of the distribution 286

and dispersity of PLA in bitumen. Two peaks can be seen in the control bitumen sample eluted 287

at retention times of 25.0 and 30.3 minutes. The two major peaks represent bitumen and are 288

present in all PLA-modified bitumen samples (Figure 9). However, Figure 10 shows that, when 289

PLA is added to the bitumen, the increase in the numbers of peaks correspond with the 290

increasing percentage of PLA (from 3, 5, 7 to 9% PLA). The distribution of PLA peaks at a 291

retention time of 25 minutes varies between samples while the major peak (at 30.3 mins) is not 292

affected. The large fragments of PLA peaks eluted at retention time 25 minutes indicate the 293

poly-dispersity of PLA within the samples. Thus, the properties of all peaks at the 25.0-minute 294

retention time were further investigated and the results are shown in Table 2. The table shows 295

that the retention time of the second major peak in all samples shifted about ± 0.1 minutes, the 296

effect of the size of exclusion column separation. The values of peak molecular weight, average 297

molecular weight, average molar mass and molar distribution (dispersity) increased with PLA 298

modification (Table 2). The varying dispersity for the 3 and 5% (1.089 and 1.136) and the 7 299

and 9% (1.653 and 1.984) bitumen-PLA indicate that the dispersity of PLA is enhanced when 300

7% and 9% of PLA were added to the bitumen. 301

1.0 1.83.2

7.39.0

11.113.2

unwashed washed

B. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 9: Gel permeable chromatography (GPC) of the control and modified bitumen 304

Bitumen

3% PLA

5% PLA

7% PLA

9% PLA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Figure 10: Zoom GPC of the control and modified bitumen 306

Table 2: Molecular properties of bitumen modified with PLA 308

Sample Retention

time (min)

Molecular

Weight

Average

Molecular

Weight

Average

molar mass

Dispersity

(Mw/Mn)

Control

Sample 25.063 1633 1253 1205 1.039

3% PLA 25.047 1659 1331 1222 1.089

5% PLA 25.154 1701 1456 1281 1.136

7% PLA 25.157 1786 2161 1307 1.653

9% PLA 25.134 1805 2749 1385 1.984

Bitumen control

3% PLA

5% PLA

7% PLA

9% PLA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

3.2. Performance of PLA-modified bitumen 310

The effect of PLA on the properties of modified bitumen was evaluated based on the physical 312

performance including; penetration, softening point, ductility and storage stability. Figure 11 313

presents the result of the penetration values of the binders. The penetration is an indication of 314

bitumen consistency, which is an empirical measure of the resistance of bitumen to continuous 315

deformation. The addition of PLA to bitumen changes the penetration value of the binders 316

(Figure 11). The bitumen added with more quantity of PLA (7% and 9%) shows low 317

penetration values as compared to the base bitumen. This indicates the ability of the PLA 318

modifier to enhance bitumen stiffness. The penetration result shows a peculiar trend, where the 319

addition of 3% of PLA increases the penetration value up to 18.5% in comparison to the base 320

bitumen, after which penetration gradually decreases with high PLA content. This is due to the 321

dispersion level of PLA in bitumen. Based on dispersity reported earlier, the dispersity of 3% 322

PLA in bitumen is low, and this has the effect of softening the binder. The gradual decrease of 323

the value observed with the addition of high amounts of PLA (5% to 9%) is due to the high 324

dispersity of PLA in bitumen. Furthermore, the high fatigue resistance and elastic recovery of 325

PLA are similar to other thermoplastic materials such as SBS, crumb rubber and natural rubber 326

and contribute to the improvement of bitumen’s consistency (Chen et al. 2007; Schaur et al. 327

2017 Airey, 2004; Chen et al. 2007; Schaur et al. 2017; Poovaneshvaran et al. 2020; and Yao 328

et al. 2018). High amounts of PLA in bitumen results in improved mechanical properties (from 329

PLA) of the modified bitumen, and as a result increases the stiffness of the binder. This increase 330

may also be due to the enhanced structural chain mobility properties of the modified bitumen. 331

Figure 11: Penetration values at 25 °C 333

Control Sample 3% PLA 5% PLA 7% PLA 9% PLA

Type of Sample

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

The softening point value of PLA-modified bitumen (Figure 12) is directly proportional 335

to the amount of PLA in bitumen. The high PLA content in bitumen increased the asphaltene 336

ratio in modified binders and this contributes to improving the stiffening properties of modified 337

bitumen. As a result, it reduces the susceptibility of the modified binder to temperature changes. 338

The less susceptibility of bitumen such as PLA modified bitumen indicated the high 339

performance of bitumen at high temperature (Zakaria et al., 2018; Al Mansoob et al., 2017). 340

This is congruent with the observation made by Poovaneshvaran et al. (2020), Rosyidi et al. 341

(2020) and Yusoff et al., (2019) about the ability of modified bitumen to withstand high 342

temperatures as compared to base bitumen. In addition, the ductility value of PLA-modified 343

bitumen is >100 cm, which is similar to the value for the base bitumen (See Table 3). The 344

physical properties of PLA-modified bitumen reported in this study are comparable with those 345

reported in earlier studies, including Al-Mansob et al. (2017), Ibrahim et al. (2016), 346

Poovaneshvaran et al. (2020) and Ali et al. (2015). 347

Figure 12: Softening point values 350

On the other hand, the main concern with polymer modified bitumen is the storage 352

stability of the modified bitumen. According to Yu et al. (2015), the modified bitumen is 353

considered stable when the difference between the softening point of the upper and lower 354

sections of the samples after storage under certain condition is less than 2.5 °C. The difference 355

in softening points of the top and bottom sections of the samples determines the degree of phase 356

separation. During high-temperature storage, the phase separation occurs when the modifier is 357

Control Sample 3% PLA 5% PLA 7% PLA 9% PLA

Type of sample

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

not dissolved in the modified bitumen and result in the non-homogeneous mixture. 358

Hosseinnezhad et al. (2019) argued that the occurrence of phase separation is influenced by the 359

solubility and particle size of the modifier and density of both the modifier and bitumen. 360

According to the literature, polymer-modified bitumen with poor storage stability is not 361

suitable for paving, roofing, and industrial specialty product applications (Isacsson et al., 1995; 362

Becker et al., 2001; Wahhab et al., 2016). 363

Bitumen modified with functionalized polymers, such as PLA, have high thermal 365

stability and no phase separation. This is indicated by the small temperature difference (<2.5 366

°C) between the top and bottom sections of the sample, except for the bitumen modified with 367

9% PLA (See Table 3). The poor thermal storage stability of the bitumen modified with 9% 368

PLA is due to the less compatibility between PLA and bitumen. 369

Table 3: Ductility and storage stability of base bitumen and PLA-modified bitumen 371

Sample Ductility at

25 °C (cm)

*Storage Stability

Top (°C) Bottom (°C) Difference (°C) Status

Control

Sample >100 - - - -

3% PLA >100 50 51 1 Good

5% PLA >100 58 60 2 Good

7% PLA >100 59 61 2 Good

9% PLA >100 68 72 4 Poor *difference between the softening point of the top and bottom sections 372

3.3 Discussion of the Results 374

In this study, polymer modification of bitumen involves the physical blending of the polymer 376

with bitumen as well as the chemical reactions between the two materials as recommended by 377

Brasileiro et al., (2019) and Cardone et al., (2014). Nuclear magnetic resonance (NMR) is a 378

spectroscopic method that can provide information about the number of magnetically distinct 379

atoms such as hydrogen nuclei (protons). NMR differs from Infrared (IR) related to the 380

approach of NMR reveals the type of functional groups present in a molecule. By combining 381

the utilization of NMR and IR spectroscopies, this study is able to gather sufficient evidence 382

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

on the chemical interactions between the bitumen and poly(lactic) acid (PLA). In NMR 383

analysis, different types of protons (H) are represented as peak signals in the spectrum having 384

different chemical shifts. The NMR of the control bitumen (Figure 2) shows that signals are 385

absorbed at a different range of chemical shift. The signals from 0.8 to 1.4 ppm in the region 386

(a) represent the protons from aliphatic alkanes. It can be concluded that most of the protons in 387

the base bitumen are alkanes, whether they are from the primary (R-CH3), secondary (R-CH2-388

R) or tertiary alkanes (R3CH). The two singlet peaks in this region indicate that these protons 389

are bonded with other functional groups (R), for instance, oxygen. The signals in the region (b) 390

are protons which represent alkenes, alkynes, aliphatic carbonyl functional group or protons 391

bonded with phenyl (aromatic as side chain). In addition, no other signals are observed in the 392

spectrums. This indicated the occurrence of other chemical shift (between 6.5 and 8.0 ppm) 393

which represented the aromatic protons. However, it is known that bitumen contains a lot of 394

aromatic compounds (Polacco et al., 2006), thus, it can be deduced that the aromatic group in 395

the bitumen is present as the phenyl group and no free protons are attached at the aromatic 396

structure. 397

The NMR spectrum of PLA (Figure 3) shows two signals, where one of the peaks is a 399

doublet, indicating the protons from the methyl group (assigned as c), and the second peak is a 400

quartet, which indicates the proton assigned as (d). Proton (d) is more shielded (appears at a 401

high chemical shift) compared to the methyl group and more electronegative when interacting 402

closely with two oxygen atoms next to each other. The results of NMR analysis of the bitumen 403

modified with 3, 5, 7 and 9% PLA (Figure 4) show that all signals from the bitumen and PLA 404

(a, b, c, and d) appear at each chemical shift. The increase in the observed intensity of the 405

signals for PLA corresponds with the increasing concentration of PLA in the samples. 406

However, the signals in the region (b) of the modified samples seem to be suppressed. The 407

suppression of the signals in this area indicates the loss of the proton absorbed at this chemical 408

shift. This is because one of the functional groups (either carbonyl groups or aliphatic 409

alkenes/alkynes) from this region interacts with PLA; this is later confirmed by the result of 410

the FT-IR analysis. 411

FT-IR analysis of the base bitumen, PLA and PLA modified bitumen (Figure 5) show 413

two additional bands at wavenumbers 1098.9 (region i) and 1749.9 cm-1 (region ii) and the 414

PLA-modified bitumen show a decrease in a band at 3600-3650 cm-1 relative to PLA. The new 415

functional groups in the PLA-modified bitumen sample (carbon-oxygen bonding (C-O) in 416

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

region i and carbonyl group (C=O) in region ii) support the result of NMR analysis. The 417

occurrence of new functional groups in the PLA-modified bitumen represented the PLA is 418

compatible with the base bitumen. The PLA and bitumen are chemically interacting with the 419

base bitumen during blending. The disappearance of the band in region iii, represented by the 420

hydroxyl group (OH), shows the reaction between the base bitumen and PLA occurring at the 421

OH group; this has resulted in the formation of new C-O and C=O bonding. However, the result 422

is not sufficient for predicting the functional group in the base bitumen reacting with the OH 423

group of the PLA. Thus, sequential dissolution was carried out to to determine the compatibility 424

of PLA with the bitumen. 425

The approach for investigating sequential dissolution was formulated by Corbett (1969) 427

and has been utilized by many researchers. Sequential dissolution is carried out to evaluate the 428

oxidation process that occurs between the binder and the bitumen. Generally, there is a net 429

reduction of maltenes fraction during an oxidation reaction, which occurs simultaneously with 430

an increase in asphaltene fraction. The formation of carbonyl functionalities within the binder 431

is linked with the increase in asphaltene during a sequential dissolution. Thus, an increase in 432

carbonyl functionalities is anticipated during the later stages of the extraction process when a 433

binder is being sequentially dissolved. In this study, sequential dissolution was used to 434

investigate the compatibility of PLA as a modifier for bitumen, thereby determining the 435

interaction of asphaltene with PLA. All samples (base bitumen and bitumen modified with 3, 436

5, 7 and 9% PLA) were washed with the same volume of chloroform (w/v). The result presented 437

in Figure 6 shows that the standard deviation does not exceed 1. The fractionation of the 438

bitumen modified with 3, 5 and 7% PLA with chloroform yielded 14.4 ± 0.8% asphaltenes, 439

slightly higher than the amount produced by the control bitumen (13.8 ± 0.2%). The lack of 440

significant difference in the value indicates absence of sequential dissolution and PLA in 441

concentrations of 3, 5 and 7% are compatible with the base bitumen. 442

The bitumen modified with 9% PLA show a ±5 % change in asphaltene content in 444

comparison to the control sample, indicating the compatibility of PLA with bitumen base does 445

not exceed 7%. A sufficient degree of polymer-bitumen compatibility is required to prevent 446

separation during storage, pumping and application of the asphalt mixture, as well as to ensure 447

required properties for pavements. Polymer modified bitumen with poor storage stability is not 448

suitable for applications such as paving binder, roofing, and other industrial speciality products 449

(Isacsson et al., 1995; Becker et al., 2001; Wahhab et al., 2016). The results of NMR and FTIR 450

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

are supported by the carbonyl index shown in Figure 6, where the carbonyl index is directly 451

proportional to the release of asphaltenes. It should be noted that the solvent used in this study, 452

i.e. chloroform, has never been reported to be one of the solvents with good compatibility with 453

bitumen. The amount of asphaltenes released due to the utilization of chloroform (13.8 ± 0.2%) 454

is lower than most of the solvents tested, such as TCE (16.7%), THF (22.5%), toluene (19.7%) 455

and decalin (22.6%) (Bowers et al. 2014). The low percentage of asphaltenes released by 456

chloroform is an indication of its high solubility. 457

FT-IR analysis of sequential dissolution was carried out to further investigate the 459

interaction between PLA and bitumen observed in the IR spectrum shown in Figure 5. The 460

washed (sequential dissolution) (WSD) and unwashed (PLA-modified bitumen) (UW) samples 461

were compared to determine the inter-correlation between the existing functional group and 462

the changes after blending. Based on the comparison of the washed and unwashed samples, it 463

can be concluded that the interaction bond between asphaltenes and PLA is dependent on the 464

carbonyl functionalities index. There is a different index pattern shown in addition to the band 465

at region i (C-O) and region ii (C=O) when divided with C=C and C-C bonds (Figure 5). 466

Overall, the C=C bond decreases while the C-C bond remains unchanged in the UW samples 467

of the control bitumen and the PLA modified bitumen. However, an increase in both the C=C 468

and C-C bonds was observed in all WSD in comparison to the control bitumen. The increase 469

in the amount of both alkenes and alkanes in the WSD is expected since both are a part of 470

asphaltene, which is the product of sequential dissolution. The difference in the number of 471

alkenes and alkanes in the UW indicates that one of them is probably involved in the chemical 472

interaction between the bitumen and the PLA. 473

From the analysis of the C-O bond in region i, the 11.2% increase in the cumulative 475

index of C-O with C=C relative to the control compared with the 2.5% decrease in that for C-476

O with C-C indicated the C-O bond formed in the PLA modified bitumen samples is related 477

to the C=C interaction. This data is supported by the result of the WSD analysis, the index for 478

C-O with C=C values remains unchanged (except for 9% PLA) while the C-O shows a decrease 479

when divided with C-C area. The same index value for C-O with C-C in the WSD indicate that 480

no C-O bond is detected in PLA because of its high compatibility with bitumen after the 481

extraction process for sequential dissolution evaluation. Analysis of the carbonyl in region ii 482

shows that the decrease in the carbonyl index of the WSD corresponds with the amount of 483

asphaltenes dissolved in chloroform. The difference in the values of both carbonyl index 484

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

between C=C (average, 15.1%) and C-C (average, 4.4%) in all PLA-modified bitumen samples 485

is due to the significantly low C=C content in the samples after modification. Based on these 486

values, it can be concluded that the interaction of bitumen with PLA is between C=C and not 487

C-C. The result of NMR analysis (Figure 4B) supports this conclusion since there is a 488

suppression of signals at a chemical shift of between 1.5 and 3.5 ppm; these signals represent 489

the alkene (C=C) group. Finally, the loss of OH group in region iii (Figure 5) in the PLA-490

modified bitumen samples seems to indicate the following reaction mechanism between PLA 491

and bitumen (Figure 13). 492

Asphaltene

AsphalteneCH3

Figure 13: Proposed reaction mechanism between PLA and bitumen 496

Generally, all the supporting data from NMR and FT-IR suggest that the reaction 498

between PLA and bitumen is an addition reaction. This reaction occurred when the hydroxyl 499

group of PLA reacts with the alkenes in bitumen, where the formation of bridge C-O bonding 500

found in the region based on FT-IR analysis. The finding is supported by the previous studies, 501

indicating the certain chemical reactions between the functional groups of the components of 502

the blends. This reaction or chemical compatibilization creates in-situ copolymers formation 503

during processing (Polacco et al., 2015; Mancini et al., 1991). This proposed mechanism is 504

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

important since the structure of PLA has high compatibility with bitumen. The finding of new 505

mechanism potentially provided the fundamental information related to the chemical 506

interaction of PLA and bitumen which lead to the discovery of new modifiers that are better 507

bitumen enhancer. 508

In addition to FT-IR analysis to determine the compatibility of PLA with bitumen, the 510

dispersity of PLA throughout the base bitumen was also examined with Gel Permeation 511

Chromatography (GPC). GPC was used to determine the molecular weight average of PLA 512

modified bitumen. The profile of GPC varies between bitumen modified with 3, 5, 7 and 9% 513

PLA relative to the control bitumen. It is worth noting that the peak eluted at ± 25.1 minutes, 514

differentiates the bitumen from the bitumen-PLA samples. The molecular properties of this 515

peak are presented in Table 2, and it shows a decline in the number of MP. The Mw, Mn and 516

polydispersity index of the samples were compared to the control sample. Mn is the statistical 517

average molecular weight of all PLA chains in the sample. Unlike Mn, Mw takes into account 518

the molecular weight of a chain in determining its contributions to the average molecular 519

weight. 520

Figure 10 and Table 2 show that there is a significant difference in bitumen modified 522

with 5% PLA (1456 gmol-1) and 7% PLA (2161 gmol-1). The heavier the chains have more 523

contribution to Mw; therefore, a better PLA-bitumen interaction is observed with 7% PLA 524

modification as compared to 3 and 5%. Polydispersity index is a measure of the distribution of 525

PLA’s molecular weight in the samples and is defined as Mw/Mn. The large polydispersity 526

index indicates the broad distribution of molecular weight. The difference in polydispersity 527

index of 5% (1.136) and 7% (1.653) PLA modification indicates that the bitumen showed the 528

best chemical interaction with the incorporation of up to 7% PLA. However, from the data of 529

sequential dissolution, the 9% PLA showed a sequential dissolution effect resulting in reduced 530

compatibility. In summary, based on the GPC and sequential dissolution data, the best 531

modification of bitumen is achieved with 7% PLA. This result is supported by the 532

characterization of the physical performance of PLA-modified bitumen. This research shows 533

that the properties of modified bitumen with 7% of PLA is the good quality in terms of 534

hardness, stiffness, ductility and storage stability ability. This is consistent with the previous 535

discussion of the chemical interaction, compatibility and dispersity test. 536

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

4. Conclusions and Suggestion for Future Study 538

This study aims to comprehensively evaluate the chemical and physical properties of PLA 540

modified bitumen. The chemical properties were monitored using NMR, FTIR and GPC, while 541

the physical properties of modified bitumen were measured by several empirical indexes in 542

terms of penetration, softening point and ductility grading. Furthermore, the storage stability 543

of the modified bitumen was also investigated in this study. The main conclusions of this 544

research are: 545

The addition of PLA into the base bitumen indicates the existence of chemical 546

interaction between these materials. The findings of this study have shown the 547

chemically cross-link at the alkene group (C=O) of PLA and hydroxyl group (OH) of 548

bitumen. 549

The results from GPC analysis shows high compatibility between the bitumen and 550

PLA. The dispersion of PLA in the bitumen is found to be directly proportional with 551

the amount of PLA, which results in the enhanced molecular properties of the PLA-552

modified bitumen. 553

The physical properties of PLA modified bitumen obtained from the conventional 554

bitumen tests show that the consistency of modified bitumen has increased as 555

compared to the base bitumen with the low penetration and high softening point value. 556

Also, ductility properties of modified bitumen indicate the permitted value as that of 557

base bitumen. 558

The modification of bitumen with up to 7% PLA is storage stable except for the 559

modified bitumen with 9% of PLA content. 560

In summary, the use of PLA in bitumen modification has a significant effect on the 561

chemical and physical properties of modified bitumen. Based on the results, 7% PLA 562

is recommended as the optimum amount for modifying base bitumen. 563

For future studies, a more comprehensive characterization of PLA modified bitumen for 564

rheology properties can be carried out. There is a need to investigate the ageing of the PLA 565

modified bitumen for the effect of oxidation and UV radiation on the rheological properties 566

and the potential deterioration over time. Moreover, further research is recommended to 567

investigate the application of PLA-modified bitumen in asphalt mixtures. 568

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Acknowledgement 570

The authors would like to express their gratitude to Universiti Kebangsaan Malaysia (UKM) 572

for the financial support of this work (DIP-2020-003). 573

Conflicts of Interest Statement 575

The authors declare that there is no conflict of interest in the publication of this paper. 577

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AUTHOR BIOGRAPHY

Nashriq Jailaini is a research assistant at the Department of Civil Engineering, Universiti

Kebangsaan Malaysia (UKM), Malaysia. His research interests are mainly in the area of

pavement engineering and pavement materials.

Ahmad Nazrul Hakimi Ibrahim is a PhD student at the Department of Civil Engineering,

Universiti Kebangsaan Malaysia (UKM), Malaysia. His research interests are mainly in the area

of highway and transportation engineering.

Dr. Abdur Rahim is a senior lecturer in the Department of Transportation Engineering and

Management, University of Engineering and Technology, Lahore, Pakistan. His research

interests are mainly in the area of pavement engineering and pavement materials.

Ir. Dr. Ahmad Kamil Arshad is a professor in the Institute for Infrastructure Engineering and

Sustainable Management, Universiti Teknologi MARA (UiTM), Shah Alam, Malaysia. His

research interests are mainly in the area of pavement engineering and pavement materials.

Ts. Dr. Norhidayah Abdul Hassan is a senior lecturer in the School of Civil Engineering,

Universiti Teknologi Malaysia (UTM), Malaysia. Her research interests are mainly in the area

of pavement engineering and pavement materials.

Ir. Dr. Nur Izzi Md. Yusoff is an associate professor in the Department of Civil Engineering,

Universiti Kebangsaan Malaysia (UKM), Malaysia. His research interests are mainly in the area

of pavement engineering and pavement materials.

Author Biography

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Author Photo

Conflicts of Interest Statement

The Authors declare that there is no conflict of interest regarding the publication of this paper.

*Conflict of Interest

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