Experimental investigation of recycled glass-fiber ...
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Experimental investigation of recycled glass- fiber reinforced thermoplastic polyurethane Analysis of tensile properties. Semen Sviridenko Degree Thesis Materials Processing Technology 2020
Transcript of Experimental investigation of recycled glass-fiber ...
Experimental investigation of recycled glass-
fiber reinforced thermoplastic polyurethane
Analysis of tensile properties.
Semen Sviridenko
Degree Thesis
Materials Processing Technology
2020
DEGREE THESIS
Arcada
Degree Programme: Materials Processing Technology
Identification number: 19973
Author: Semen Sviridenko
Title: Experimental investigation of recycled glass-fiber rein-
forced thermoplastic polyurethane
Supervisor (Arcada): Harri Anukka
Commissioned by:
Abstract:
With the growing number of glass-fiber reinforced composite waste generated each year,
the issue of composite waste management becomes recognizable. Mechanical recycling is
a well-investigated recycling pathway. Tensile Testing is one of the fundamental investi-
gative tools used in materials’ sciences. It can be used to compare the recycled material
with the virgin. The aim of this thesis work is to investigate the mechanical properties of
recycled glass-fiber reinforced thermoplastic polyurethane. Effect of drying of the compo-
site prior to manufacturing was investigated. Comparison was made with the virgin com-
posite. Material’s behavior under manufacturing and processing conditions was investi-
gated. In total, four material groups were formulated, manufactured, and tested: dried re-
cycled composite, undried composite, recycled composite with 12.5% virgin composite by
weight, and virgin composite. Specimens were tested for Tensile Strength and Percent
Elongation at Break. Dried and Undried composite showed a loss of 22 % and 27.3 % of
Tensile Strength. Similarly, Dried and Undried composite showed a loss of 9.17 % and
16.7 % in Percent Elongation at Break. Compounded composite showed a loss of 6.3 % if
Tensile strength and a gain of 7.6 % in Percent Elongation at Break. Mechanical recycling
appears to result in the loss of mechanical properties in recycled composite. Compounding
the recycled composite with the virgin results in greater retention of Tensile Strength and
a minor gain in Percent Elongation at Break. Based on the findings, it cannot be concluded
that drying the recycled composite improves the retention of mechanical properties.
Keywords: Recycling, Fiber, Glass-fiber, Thermoplastic, Injection
molding, Tensile Strength, Percent Elongation at Break
Number of pages: 36
Language: English
Date of acceptance:
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TABLE OF CONTENTS
1 INTRODUCTION ................................................................................................... 6
2 LITERATURE REVIEW ......................................................................................... 9
2.1 MECHANICAL RECYCLING OF GLASS-FIBER REINFORCED THERMOPLASTIC
COMPOSITE WASTE ............................................................................................................... 9
2.2 INJECTION MOLDING ................................................................................................ 10
2.3 TENSILE TESTING ..................................................................................................... 12
3 METHOD ............................................................................................................. 15
3.1 MATERIAL ................................................................................................................... 16
3.1.1 WASTE FRACTION RECYCLED ........................................................................ 16
3.2 PREPARATION ........................................................................................................... 17
3.2.1 MECHANICAL RECYCLING OF THE WASTE ................................................... 17
3.2.2 MATERIAL GROUPS .......................................................................................... 17
3.2.3 INJECTION MOLDING OF THE TENSILE TEST PIECES ................................. 18
3.2.4 TENSILE TEST DEFINITIONS AND SPECIMEN DIMENSIONS ....................... 19
4 RESULTS ............................................................................................................ 20
4.1.1 UNDRIED RECYCLED GFRTPU + 0.09 % MASTERBATCH BY WEIGHT ...... 20
4.1.2 DRIED RECYCLED GFRTPU + 0.09 % MASTERBATCH BY WEIGHT ............ 21
4.1.3 12.5 % VIRGIN GFRTPU + 0.09 % MASTERBATCH BY WEIGHT ................... 23
4.1.4 VIRGIN GFRTPU + 0.09 % MASTERBATCH BY WEIGHT ............................... 24
5 DISCUSSION ...................................................................................................... 25
5.1 ANALYSIS OF ENGINEERING PROPERTIES .......................................................... 25
5.1.1 TENSILE STRENGTH ......................................................................................... 27
5.1.2 PERCENT ELONGATION AT BREAK ................................................................ 28
6 CONCLUSION..................................................................................................... 29
REFERENCES ........................................................................................................... 31
4
TABLES
Table 1. Formulated material groups .............................................................................. 18
Table 2..IM machine temperature readings for the heating zones taken during
manufacturing of tensile test specimens. ........................................................................ 18
Table 3. Standard deviation for Tensile Strength ........................................................... 27
Table 4. Standard deviation for % Elongation at Break ................................................. 29
FIGURES
Figure 1.The adopted recycling methods (Karuppanan and Kärki, 2020) ..................... 10
Figure 2. Units of an injection molding machine (Fernandes et al., 2016) .................... 11
Figure 3. Graph of Load (N) against Extension (mm). (Yunus, et al., 2014)................. 13
Figure 4. Stress strain curve for tensile test […]. (Md Koushic, et al., 2020) ................ 14
Figure 5.Plasticizing waste and runners […].................................................................. 16
GRAPHS
Graph 1. Average Force vs. Average Elongation for Undried Recycled GFRTPU ....... 20
Graph 2. Average Stress vs. Average Strain for Undried recycled GFRTPU ................ 21
Graph 3. Average Force vs. Average Elongation for Dried Recycled GFRTPU ........... 22
Graph 4. Average Stress vs. Average Strain for Dried Recycled GFRTPU .................. 22
Graph 5. Average Force vs. Average Elongation for 12.5 % Virgin GFRTPU ............. 23
Graph 6. Average Stress vs Average Strain for 12.5 % Virgin GFRTPU ...................... 24
Graph 7. Average Force vs. Average Elongation for Virgin GFRTPU ......................... 24
Graph 8. Average Stress vs. Average Strain for Virgin GFRTPU ................................. 25
Graph 9. Average Force vs. Average Elongation for all material groups tested. ........... 26
Graph 10. Average Stress vs. Average Strain for all material groups tested. ................ 26
Graph 11. Average Tensile Strength values obtained for all material groups tested. .... 27
Graph 12. Average Percent Elongation at Break values obtained for all material groups
tested. .............................................................................................................................. 28
5
SYMBOLS
𝜎 – Engineering stress
𝑠𝑢 – Tensile Strength
𝑃 - Force
𝑃𝑚𝑎𝑥 – Maximum force sustained by the specimen prior to failure
𝐴0 – Initial cross-sectional area
𝑒 – Engineering strain
∆𝐿 – Change in length
𝐿 –Instantenious gage length
𝐿0 – Original gage length
𝑠 − Estimated standard deviation
𝑋 – Value of a single observation
𝑛 − Number of observations
�̅� – Aritmetic mean of the set of observations
APPENDICES
Appendix 1.Force vs. Elongation curves for each specimen of Undried Recycled
GFRTPU plotted on a single frame of reference. ........................................................... 33
Appendix 2. Stress vs. Strain curves for each specimen of Undried Recycled GFRTPU
plotted on a single frame of reference. ........................................................................... 33
Appendix 3. Force vs. Elongation curves for each specimen of Dried Recycled GFRTPU
plotted on a single frame of reference. ........................................................................... 34
Appendix 4. Stress vs. Strain curves for each specimen of Dried Recycled GFRTPU
plotted on a single frame of reference. ........................................................................... 34
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Appendix 5. Force vs. Elongation curves for each specimen of 12.5 % Virgin GFRTPU
plotted on a single frame of reference. ........................................................................... 35
Appendix 6. Stress vs. Strain curves for each specimen of 12.5 % Virgin GFRTPU plotted
on a single frame of reference. ....................................................................................... 35
Appendix 7. Force vs. Elongation curves for each specimen of Virgin GFRTPU plotted
on a single frame of reference. ....................................................................................... 36
Appendix 8. Stress vs. Strain curves for each specimen of Virgin GFRTPU plotted on a
single frame of reference. ............................................................................................... 36
1 INTRODUCTION
Glass-fiber reinforced composites (GFRCs) represent a valuable class of engineered ma-
terials. GFRCs are a class of composites, consisting of a glass fiber reinforcing material
with the matrix resin holding fibers in position. (Composites World, 2016) Depending on
the specific formulation of the matrix and reinforcing materials, properties of a particular
composite can be tailored to better suit industrial needs. Sathishkumar, et al., (2014 p.
1258-1275) composed a comprehensive review on mechanical properties of different for-
mulations of GFRCs, grades of glass-fiber used in such composites, and manufacturing
techniques. Authors also note primary applications of GFRCs – electronics industry,
home and furniture industries, aviation and aerospace industries, boats, and marine indus-
tries, medical, and automotive industries.
In 2020, the global glass-fiber capacity was 12.8 billion pounds, and the industry demand
was 10.7 billion pounds. Compared to 2015, when the demand achieved 10.5 billion
pounds with industry capacity of 11.1 billion pounds. (Mazumdar, et al., 2021) GFRCs
are seeing increased use in wind energy sector. GFRCs and carbon-fiber reinforced com-
posites (CFRCs) are the primary materials used for the production of wind turbine rotor
blades. Most of the rotor blades are designed to have a lifetime of 20-25 years. (Jensen &
Skelton, 2018) According to the public report by American Wind Energy Association
(2020 p. 4), during the first three quarters of 2020, the U.S. wind industry commissioned
6309 MW worth of new wind power capacity, which constitutes a 72 % increase over the
first three quarters in 2019.
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With the increased demand for GFRCs comes an issue of waste disposal. Parts, reaching
end-of-life stage, production waste and failed parts all contribute to the growing number
of GFRC waste. It was estimated, that by the year 2030, 100000 tons worth of end-of-life
wind turbine blades will be cumulated every year. (The European Wind Energy Associa-
tion, 2014).
One of the approaches of dealing with the increasing amounts of GFRCs is recycling. An
overview of the current recycling strategies and mechanical recycling in particular is pre-
sented in the literature review part of the investigation.
There are numerous investigative tools available to determine the mechanical properties
of materials. They can be classified into tension, compression, shear, flexure, impact,
fracture, and fatigue (Bibo et al., 2000). Tension, or tensile testing is performed on com-
posite materials to determine ultimate tensile stress and Tensile Modulus. However, God-
win (2000 p. 43) notes, that observations made during tensile test performed under con-
trolled conditions provide additional insights into material’s behavior. The failure nature
can be seen and information about damage initiation and development can be observed.
The aim of this thesis work is to investigate the effect of mechanical recycling on the
mechanical properties of short random-oriented glass-fiber reinforced thermoplastic pol-
yurethane and to record the recycling and sample manufacturing process. Additional aim
of this investigation is to determine the effect of drying of the composite prior to manu-
facturing on mechanical properties. The motivation behind this aim is to determine
whether this manufacturing step has an effect on mechanical properties of the recycled
material and whether this step could possibly be omitted during an established recycling
operation. Finally, this investigation aims to investigate the effect of compounding virgin
material with the recycled composite.
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The objectives of this thesis work are:
• Perform tensile testing in accordance with the ASTM D638-14 standard. Obtain
average values for the Tensile Strength and Elongation at Break for each set of
the specimens. Compare the experimental values with the virgin material.
• Measure the impact of drying the composite prior to manufacturing on Tensile
Strength and Percent Elongation at Break
• Measure the impact of compounding the recycled composite with 12.5 % virgin
composite by weight on Tensile Strength and Percent Elongation at Break
The theoretical framework for determination of relevant mechanical properties in this in-
vestigation was based upon the second edition of Tensile Testing by J.R Davis (Davis,
2004). This work provided the necessary equations and definitions for Tensile Strength
and provided insights into tensile behavior of composite polymeric materials. The actual
setup configuration, testing apparatus requirements, testing procedures, definitions of me-
chanical properties, reporting structure and mathematical base for data analysis were
adopted from the ASTM D-638-14 standard for tensile properties of plastics (ASTM In-
ternational, 2014). This standard aided during the process of specimen dimension selec-
tion and speed of testing selection. Calculation of relevant properties and necessary
graphs were produced using MS Excel software.
The overview of the current state of glass-fiber reinforced thermoplastic composite in-
dustry and latest recycling strategies was based upon various scientific articles. Emphasis
was put on thermoplastic glass-fiber reinforced composites and mechanical recycling.
Description of injection molding process was taken from Basics of Polymers: Fabrication
and Processing Technology by S. Muralisrinivasan. (Muralisrinivasan, 2015)
This investigation is structured in way that presents the chronological order of each man-
ufacturing step to provide an opportunity to retrace the operational steps with the exact
manufacturing parameters.
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2 LITERATURE REVIEW
This chapter of the thesis serves to introduce the reader to the current recycling strategies
of glass-fiber reinforced composites and glass-fiber reinforced thermoplastic composites
in particular. In addition, it provides an overview of the industrial processes that the ma-
terial underwent during the investigation. Lastly, this chapter provides an overview of
tensile testing and the description of mathematical formulas used to obtain the relevant
properties.
2.1 MECHANICAL RECYCLING OF GLASS-FIBER REIN-
FORCED THERMOPLASTIC COMPOSITE WASTE
Recycling is an umbrella term which includes various processing and treatment tech-
niques applied to the discarded material, coming in the form of production waste and end-
of-life products. As the use of fiber-reinforced composites is increasing in e.g., aircraft
manufacturing and wind turbine manufacturing industries, problem of waste disposal and
waste utilization becomes recognizable. The majority of composites contributing to the
waste generated are that belonging to GFRC and CFRC. Current trend in the composite
recycling industry is to further reduce the amount of material that undergoes incineration
and landfilling. Recycling methods can be classified into several broad categories: me-
chanical recycling, thermal recycling, and chemical recycling. (Karuppannan and Kärki,
2020) These methods are summarized in Figure 1 and specific methods are presented.
Mechanical recycling is a technique that involves size reduction of the scrap composites,
usually by means of cutting, crushing or milling. The recycled material is then separated
into fiber-rich (fine) and matrix-rich (coarse) fraction. Most of the research concerning
this method focuses on applying mechanical recycling to GFRC waste, although it can be
used to recycle CFRCs as well.
Such a process implies the loss of particular fiber orientation that may have been present
in the original composite. The physical integrity of the fibers is disturbed as well. De-
pending on the recycling objective, the fine fraction can be used as filler or as reinforce-
ment. (Karuppannan and Kärki, 2020)
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Mechanical recycling is an attractive option for the thermoplastic-matrix composites as it
can be incorporated in the existing continuous industrial production, such as in injection
molding production line. Since the waste stream typically consists of one type of material,
little additional separation is required. Compared to the advanced thermochemical tech-
niques and alternative approaches, the apparatus and energy requirements are modest as
well. However, due to the fiber breakage and fiber orientation loss induced by this ap-
proach, material loses the desired strength and stiffness, which leads to value loss of the
material. (Yang, et al., 2012)
Figure 1.The adopted recycling methods (Karuppanan and Kärki, 2020)
2.2 INJECTION MOLDING
This subchapter serves to provide an overview of the injection molding and extrusion. In
addition, in this subchapter typical operational steps are presented.
Injection molding (IM) is a widely used manufacturing method for thermoplastic GFRC
products. IM is an established industrial mass-manufacturing technology, and the process
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can be divided into distinct steps. Basic overview of a typical injection molding machine
and its’ components can be found in Figure 2. Depending on the design of the product
and correspondingly the mold, this manufacturing method inherently produces waste in
form of runners, sprues, and gates. Waste can arise if defects, such as flashing, are present
on the finished part. Failed parts and plasticizing waste represent additional sources of
waste.
Figure 2. Units of an injection molding machine (Fernandes et al., 2016)
Characteristic steps of a typical injection molding process are given below.
1. Polymer pellets are simultaneously conveyed, melted and plasticated within the
barrel.
2. Injection is done under pressure in the mold.
3. Mold is filled and packed.
4. Polymeric material is cooled below its glass transition temperature.
5. Cooling process consumes major share of the molding cycle.
6. The mold is open, and the part is ejected, and the cycle is repeated.
The material in form of granulates is supplied through the hopper to the feed zone of the
machine. It is then conveyed along the barrel by means of reciprocating screw and is
melted and plasticated by means of friction and heating. The material is then forcefully
injected through the nozzle into the relatively cold closed mold cavity. To compensate for
shrinkage, packing takes place, during which additional material is supplied to the mold.
The material rapidly cools and once the gate into the mold closes no more material can
be supplied. The mold opens and the finished product is ejected from the mold and the
cycle is repeated. (Muralisrinivasan, 2015)
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2.3 TENSILE TESTING
Tensile testing is one of the fundamental testing methods in material science. It is a de-
structive test during which the specimen is secured tightly in a Universal Testing Machine
and is subjected to a constant load and an attempt is made to cause the material to fail.
Throughout the test, force and elongation values are recorded and desired engineering
properties can be subsequently extracted from the data. (Davis, 2004) Tensile testing is
one of the most common tests in material science due to several reasons. It is easy to
perform, the specimen design is simple – specimens can be either machined or directly
cast, the equipment required for testing is commonly found in material laboratories and
the testing can be performed quickly. (Suryanarayana, 2011)
A force-elongation curve, also called load-extension curve can be created from these re-
cordings, which gives a general idea of specimen behavior under predefined test condi-
tions. Further analysis requires converting the force values to engineering stress values
and elongation values to engineering strain values in order to obtain the stress-strain
curve. Formulas and definitions for engineering stress and strain are given in Equations
1 and 2 correspondingly. Examples of force-elongation and stress-strain curves are given
in Figures 3 and 4 correspondingly.
Godwin (2000 p. 50-51) notes that speed of testing is an important parameter to consider
when defining the tensile test. If an appropriate speed of testing is not selected, important
information may be lost in the intervals between data points. This suggests that the slower
speed of testing will result in more data points gathered during the test, from which a
more accurate picture of material’s behavior can be gathered.
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Figure 3. Graph of Load (N) against Extension (mm). (Yunus, et al., 2014)
𝜎 =𝑃
𝐴0 ; [1]
Where 𝜎 is engineering stress, P is the force, and 𝐴0 is the original cross-sectional area
of the specimen. Engineering stress is defined as the average longitudinal stress in the
tensile specimen. It is obtained by dividing the load measured in Newtons (N) by the
original cross-sectional area measured in meters squared (𝑚2). The corresponding unit of
engineering stress is Pascals (Pa).
𝑒 =∆𝐿
𝐿0=
𝐿 − 𝐿0
𝐿0; [2]
Where e is the engineering strain, ∆𝐿 is the change in gage length, 𝐿0 is the original gage
length, and 𝐿 is the instantaneous gage length. Engineering strain is defined as the average
linear strain and is obtained by dividing the elongation of the gage length in millimeters
(mm) by original gage length in millimeters. Following the definition, engineering strain
is a unitless property.
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Figure 4. Stress strain curve for tensile test in JGJG composite. (Md Koushic, et al., 2020)
Once the values for stress and strain are obtained further properties can be derived.
Tensile strength or ultimate tensile strength is an often-reported value from tensile test
results. Mathematical definition for tensile strength is given below in Equation 3:
𝑠𝑢 =𝑃𝑚𝑎𝑥
𝐴0; [3]
Where 𝑠𝑢 is the tensile strength, and 𝑃𝑚𝑎𝑥 is the maximum force sustained by the spec-
imen during the test. It is defined as the maximum force divided by the original cross-
sectional area. Due to the long practice of using this property and due to the ease of re-
production, tensile strength is a valuable design criterion, especially for the brittle mate-
rials as is often the case for fiber-reinforced composites. (Davis, 2004)
Another property which can be derived from the tensile test data is percent elongation at
break. It represents the maximum elongation of the specimen achieved during the test
prior to failure. Percent elongation at break is a valuable property for design and is rela-
tively easy to reproduce. (ASTM International, 2014)
15
Another property used during data analysis is Standard Deviation (𝑠). Standard deviation
provides a measure of variability of the set of data. It can also be described as a measure
of the width of the distribution of the measurements (Turner, 2000 p. 20). Standard devi-
ation and the variance are used to determine the precision and accuracy of the data
(Thomas, 2014). Variance can be obtained by taking the square of the standard deviation
(Turner 2000 p. 21). Variance can be measured against either the mean value or the
boundary condition (e.g., target value or a known value obtained from a separate refer-
ence). Used against a boundary condition, standard deviation and variance are ineffective
at serving as the measure of quality of the data and the use of other mathematical tools is
justified (Turner 2000 p. 21). The use of variance and standard deviation is justified in
cases in which the specimen population exhibits a unimodal excitation response (Turner
2000 p. 21). Mathematical definition for standard deviation is given below in Equation 4
(ASTM International, 2014). In practice, the smaller the standard deviation, the closer
individual measurements for a given value are to the mean value, meaning, that the same
value can be obtained consistently throughout the test.
𝑠 = √(∑ 𝑋2 − 𝑛�̅�2)
(𝑛 − 1); [4]
Where 𝑠 is the estimated standard deviation, 𝑋 is the value of a single observation, 𝑛 is
the number of observations and �̅� is the arithmetic mean of the set of observations.
(ASTM International, 2014)
3 METHOD
This chapter of the thesis focuses on describing the material investigated, the tensile test-
ing machine and injection molding machine used during the investigation, tensile test
conditions and definitions and the observations recorded during tensile test piece produc-
tion and mechanical recycling.
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3.1 MATERIAL
The material investigated in this thesis is glass-fiber reinforced thermoplastic polyure-
thane (GFRTPU). It is engineered to be specifically applied in injection molding pro-
cesses. Reinforcement consists of random-oriented short glass fibers. Reinforcing mate-
rial constitutes to 50 % of the weight of the composite and the matrix material belongs to
polyester-urethanes class.
Recycled material was compounded with black coloring additive, otherwise known as
masterbatch. The masterbatch belongs to polyester family of materials.
3.1.1 WASTE FRACTION RECYCLED
The material investigated came in the form of runners, sprues, gates, failed parts, trim-
mings, and plasticizing waste left over after the conclusion of small-scale injection mold-
ing production project. It was estimated that the waste corresponds to 11.7 % of the total
mass of material being used for the production. An example of typical waste constituents
is presented in Figure 5.
Figure 5.Plasticizing waste and runners, representing the majority of the waste recycled.
17
3.2 PREPARATION
This subchapter serves to document the exact preparation steps which occurred in order
to produce tensile test pieces. In addition, it documents the production parameters during
injection molding sessions, such as screw RPM and heating zones temperatures. Obser-
vations during mechanical recycling and injection molding are provided. Material sets
formulations are documented as well. Finally, tensile test definitions are provided.
3.2.1 MECHANICAL RECYCLING OF THE WASTE
The waste fraction was collected and ground using Rapid Granulator. Model of the gran-
ulator used does not possess the capacity for precise drive RPM control and has a fixed
blade system. Recycling had to be performed in small batches, as large agglomerates of
composite waste, e.g., plasticizing waste, resulted in stoppages as the blades of the gran-
ulator were unable to break down clusters of composite waste. The average size of the
resulting recycled material was measured. A sample of recycled material was measured
laterally and longitudinally using Vernier caliper. It was found that the recycled material
was on average 9.381 mm long and 2.83 mm wide based on 10 measurements. The appar-
ent directional non-uniformity is most likely due to the shape of the sprues, as they, along
with the runners, represent the majority of the waste.
3.2.2 MATERIAL GROUPS
During this investigation, 4 material groups have been formulated and tested. First, the
virgin composite compounded with 0.09 % of masterbatch by weight. Secondly, the re-
cycled composite that has been subjected to drying. Thirdly, composite that has been left
undried. Lastly, the mixture of recycled and virgin composite, where the virgin composite
represents 12.5 % of the weight content. Summary of material groups tested is provided
in Table 1. Following the ASTM D638-14 standard, 10 specimens of Type I tensile test
pieces were manufactured for each set (ASTM International, 2014).
18
Table 1. Formulated material groups.
MATERIAL GROUPS
Undried Recy-
cled GFRTPU
Dried Recy-
cled
GFRTPU
12.5 % Virgin
GFRTPU by
weight
Virgin
GFRTP
U
Masterbatch
weight content, %
0.09 0.09 0.09 0.09
Drying time, hours 0 3 4 3
Drying tempera-
ture, ℃
104 104 104 104
Samples manufac-
tured, pieces
10 10 10 10
3.2.3 INJECTION MOLDING OF THE TENSILE TEST PIECES
Injection molding of the tensile test pieces was performed on a Sumitomo Shi Demag
IntElect 100-450 injection molding machine. The manufacturing of products and the as-
sociated composite waste was also performed on the same injection molding machine.
Tensile test piece manufacturing was performed during 2 separate sessions. During the
first session, the virgin composite was processed. Dried and undried composite were pro-
cessed during the first session as well. No purging was performed in between specimen
set production. During the second session, the 12.5% virgin composite by weight set of
material was processed. The screw speed was set to be 50 RPM. The temperature profile
of the injection molding machine heating zones for each session are presented in Table 3.
Table 2..IM machine temperature readings for the heating zones taken during manufacturing of tensile test specimens.
Session Nozzle,℃ Zone 3, ℃ Zone 2, ℃ Zone 1℃ Feed, ℃
1 240 240 236 225 30
2 230 227 219 213 60
19
During the production of the tensile test specimens no issues regarding the processing of
the composite have been recorded.
3.2.4 TENSILE TEST DEFINITIONS AND SPECIMEN DIMENSIONS
Tensile testing was performed at room temperature on a Testometric M 350-5CT Univer-
sal Testing Machine.
Following the ASTM D-638-14 standard the speed of testing for all sets of material was
selected to be 5 𝑚𝑚
𝑚𝑖𝑛. This speed of testing was selected as the slowest speed of testing
permitted by the standard to ensure the minimal interval between the data points. (ASTM
International, 2014) The average length of the narrow section of the tensile test pieces
was 90 mm, the width was 13 mm and the thickness 3 mm. Correspondingly, the original
cross-sectional area of the tensile test pieces was 39 𝑚𝑚2
20
4 RESULTS
This chapter of the thesis focuses on the tensile test results and tensile test observations.
In addition, average force - average elongation and average stress – average strain curves
for all the specimens tested are presented.
4.1.1 UNDRIED RECYCLED GFRTPU + 0.09 % MASTERBATCH BY WEIGHT
Graph 1. Average Force vs. Average Elongation for Undried Recycled GFRTPU
A force-elongation curve was constructed from the force-elongation readings from the
tensile test. Arithmetic means for the force values and for the elongation values were
calculated. The average force – average elongation curves for all the specimens are pre-
sented in Graph 1. In total, 10 specimens of recycled undried GFRTPU were tested during
this investigation. Individual force-elongation curves plotted on a single graph can be
found in Appendix 1.
During the tests, it was reported that the material exhibits brittle behavior. This observa-
tion holds true for all material sets. Supporting this observation, force-elongation curves
suggest that material is brittle, with pronounced initial linear portion of the curve and
reduced necking section with a sudden fracture.
0
500
1000
1500
2000
2500
3000
3500
0 2 4 6 8 10 12
Ave
rage
Fo
rce
(N)
Average Elongation (mm)
Undried Recycled GFRTPU - Average Force vs. Average Elongation
21
After the construction of force-elongation curves it was possible to convert the force val-
ues into the engineering stress values using Equation 1 and elongation readings into the
engineering strain values using Equation 2. Average stress – average strain curves for all
the specimens are presented in Graph 2. Individual stress-strain curves plotted on a single
graph can be found in Appendix 2.
However, the data for the Undried Recycled GFRTPU exhibits anomalous and irregular
behavior. Individual samples of Undried Recycled GFRTPU exhibit considerable varia-
tion during the test. This is evident by the data presented in Appendix 1. Such material
behavior presents issues during stress and strain calculations. Due to denominator for both
stress and strain being single constant values, the resulting shape of the stress-strain curve
is identical to that of force-elongation curve.
Graph 2. Average Stress vs. Average Strain for Undried recycled GFRTPU
4.1.2 DRIED RECYCLED GFRTPU + 0.09 % MASTERBATCH BY WEIGHT
Following the same procedure for the analysis of undried composite test data, it was pos-
sible to construct the force-elongation and the stress-strain curves. The average force-
average elongation and the average stress-average strain curves are presented in Graphs
3 and 4 accordingly. Individual force elongation and individual stress-strain curves pre-
sented on individual frames of references can be found in Appendix 3 and 4
0
10
20
30
40
50
60
70
80
90
0 0,02 0,04 0,06 0,08 0,1 0,12 0,14
Ave
rage
Str
ess
(MP
a)
Average Strain (%)
Undried Recycled GFRTPU - Average Stress vs. Average Strain
22
correspondingly. In total, 10 specimens of Recycled Dried GFRTPU were tested during
this investigation.
Graph 3. Average Force vs. Average Elongation for Dried Recycled GFRTPU
Graph 4. Average Stress vs. Average Strain for Dried Recycled GFRTPU
0
500
1000
1500
2000
2500
3000
0 2 4 6 8 10
Ave
rage
Fo
rce
(N)
Average Elongation (mm)
Dried Recycled GFRTPU - Average Force vs. Average Elongation
0
10
20
30
40
50
60
70
0 0,02 0,04 0,06 0,08 0,1 0,12
Ave
rage
Str
ess
(MP
a)
Average Strain (%)
Dried Recycled GFRTPU- Average Stress vs. Average Strain
23
4.1.3 12.5 % VIRGIN GFRTPU + 0.09 % MASTERBATCH BY WEIGHT
Graph 5. Average Force vs. Average Elongation for 12.5 % Virgin GFRTPU
Following the same procedures, it was possible to obtain force-elongation and the stress-
strain curves for the 12.5 % Virgin GFRTPU by weight. The average force – average
elongation and average stress – average strain curves are correspondingly presented in
Graphs 5 and 6. Individual force elongation and individual stress-strain curves presented
on individual frames of references can be found in Appendix 5 and 6 correspondingly. In
total, 10 specimens of 12.5 % Virgin GFRTPU by weight were tested during this investi-
gation.
0
500
1000
1500
2000
2500
3000
3500
0 2 4 6 8 10 12 14
Ave
rage
Fo
rce
(N)
Avergae Elongation (mm)
12.5 % Virgin GFRTPU by wt. - Avg. Force vs. Avg Elongation
24
Graph 6. Average Stress vs Average Strain for 12.5 % Virgin GFRTPU
4.1.4 VIRGIN GFRTPU + 0.09 % MASTERBATCH BY WEIGHT
Graph 7. Average Force vs. Average Elongation for Virgin GFRTPU
Following established analysis procedures, it was possible to convert the force values into
engineering stress values and elongation values into engineering strain values. The aver-
age force - average elongation and average stress- average strain curves are presented in
Graphs 7 and 8 accordingly. Individual force elongation and individual stress-strain
curves presented on individual frames of references can be found in Appendix 7 and 8
0
10
20
30
40
50
60
70
80
90
0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16
Stre
ss (
MP
a)
Strain (%)
12.5 % Virgin GFRTPU by wt. - Avg. Stress vs. Avg. Strain
0
500
1000
1500
2000
2500
3000
3500
4000
0 2 4 6 8 10 12 14
Ave
rage
Fo
rce
(N)
Average Elongation (mm)
Virgin GFRTPU + 0.09 % Masterbatch by wt. -Average Force vs. Average Elongation
25
correspondingly. In total, 10 specimens of Virgin GFRTPU were tested during this inves-
tigation.
Graph 8. Average Stress vs. Average Strain for Virgin GFRTPU
5 DISCUSSION
This chapter focuses on the analysis of obtained engineering properties and error analysis.
The behavior of material is explained.
5.1 ANALYSIS OF ENGINEERING PROPERTIES
Graphs 9 and 10 contain average force – average elongation curves and average stress-
average strain curves, correspondingly, for all material groups tested presented on a single
point of reference. Due to nonuniformity of results for undried recycled material group
and for virgin material group, the average force – average elongation curves for these
material groups exhibit an erratic behavior towards the breaking point, thus rendering the
latter part of the curve misrepresentative of the typical material behavior. This point holds
true for the average stress – average strain curves as well due to a denominator being a
constant value for engineering stress and engineering strain values.
0
10
20
30
40
50
60
70
80
90
100
0 0,02 0,04 0,06 0,08 0,1 0,12 0,14
Ave
rage
Str
ess
(MP
a)
Average Strain (%)
Virgin GFRTPU + 0.09 % Masterbatch by wt. -Average Stress vs. Average Strain
26
Graph 9. Average force vs. average elongation for all material groups tested.
Graph 10. Average stress vs. average strain for all material groups tested.
After construction of the force-elongation and stress-strain curves was complete, it was
possible to determine the Tensile Strength using Equation 3. From the force-elongation
curves it was possible to determine the Percent Elongation at Break for each specimen.
0
500
1000
1500
2000
2500
3000
3500
4000
0 2 4 6 8 10 12 14
Ave
rage
Fo
rce
(N)
Average Elongation (mm)
Material Groups Tested - Average Force vs. Average Elongation
Undried Recycled Dried Recycled Recycled + 12.5 % Virgin by wt. Virgin
0
10
20
30
40
50
60
70
80
90
100
0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16
Stre
ss (
MP
a)
Strain (%)
Material Groups Tested - Average Stress vs. Average Strain
Undried Recycled Dried Recycled Recycled + 12.5 % Virgin by wt. Virgin
27
Following the ASTM D638-14 standard, standard deviation was also calculated for each
engineering property for each specimen set using Equation 5.
5.1.1 TENSILE STRENGTH
Graph 11 contains the summary of obtained average Tensile Strength values for each set
of material tested. Standard deviation for Tensile Strength for each specimen set was cal-
culated. The values for each material set are presented in Table 3.
Graph 11. Average Tensile Strength values obtained for all material groups tested.
Table 3. Standard deviation for Tensile Strength
Tensile
Strength
Recycled,
Undried
Recycled,
Dried
12.5 % by wt. Virgin, Experi-
mental
Standard devi-
ation
6.242 1.096 1.075 4.143
Both dried and undried recycled material show the loss of Tensile Strength. Undried com-
posite showed a loss of 22.2 % of Tensile Strength compared to the experimental values
for the virgin composite.
67,002962,6638
80,683186,0982
0
10
20
30
40
50
60
70
80
90
100
Ten
sile
Str
engt
h (
MP
a)
Tensile Strength, Summary
RECYCLED, UNDRIED
RECYCLED, DRIED
12.5 % VIRGIN BY WT.
VIRGIN, EXPERIMENTAL
28
Dried composite showed a loss of 27.3 % of Tensile Strength when compared to the ex-
perimental values.
It appears, that drying of the recycled material did not result in greater retention of Tensile
Strength, but such an assumption can be misleading, as the standard deviation of the av-
erage Tensile Strength for the dried composite is relatively large. This fact suggests that
the value may not be reliably reproductible if the drying step is omitted during the pro-
cessing of the composite.
However, the data suggest that mechanical recycling of the composite results in the min-
imal loss of 22.2 % and the maximum is 27.3 % compared to the experimental values for
the virgin composite.
Compounding of the recycled material with the virgin composite appears to produce a
minor loss of Tensile Strength, compared to the experimental data.
5.1.2 PERCENT ELONGATION AT BREAK
Graph 12 contains the summary of obtained average Percent Elongation at Break values
for each set of material tested. Standard deviation was calculated. The values for each
material set are presented in Table 4.
Graph 12. Average Percent Elongation at Break values obtained for all material groups tested.
10,74059,8546
12,723811,8253
0
2
4
6
8
10
12
14
Elo
nga
tio
n a
t B
reak
(%
)
Percent Elongation at Break, Summary
RECYCLED, UNDRIED
RECYCLED, DRIED
12.5 % BY WT.
VIRGIN, EXPERIMENTAL
29
Table 4. Standard deviation for % Elongation at Break
% Elongation
@ Break
Recycled,
Undried
Recycled,
Dried
12.5 % by wt. Virgin, Experi-
mental
Standard Devi-
ation
1.008 0.36 0.376 0.666
Such a disparity between the compounded and experimental virgin composite can be ex-
plained by the test data for the experimental virgin composite being more variable. the
standard deviation for experimental virgin composite is relatively high, at 0.666. This fact
suggests that the same value for percent elongation at break cannot be reliably derived
from the test data obtained.
Both dried and undried recycled composite show a loss of average 3 % of elongation at
break. It appears that drying of the recycled material did not result in a significant im-
provement in elongation at break. However, by looking at the standard deviation for the
undried recycled composite, it can be concluded that the data is highly variable, pos-
sessing the largest standard deviation among all material sets tested.
6 CONCLUSION
During this investigation average Tensile Strength values and average Percent Elongation
at Break values were obtained for the investigated material groups. Undried recycled
GFRTPU achieved an average of 67 MPa of Tensile strength, Dried Recycled GFRTPU
achieved an average of 62. 7 MPa of average Tensile Strength, 12.5 % Virgin GFRTPU
by weight composite achieved an average of 80.7 MPa of Tensile Strength and virgin
GFRTPU achieved an average of 86 MPa of Tensile Strength.
Experimental Percent Elongation at Break values obtained were 10.74 % for Undried
Recycled GFRTPU, 9.85 % for Dried Recycled GFRTPU, 12.72 % for 12.5 % Virgin
GFRTPU by weight composite, and 11.82 % for the Virgin GFRTPU.
30
Compared with the Virgin GFRTPU, Undried Recycled GFRTPU sustained the greatest
loss of Tensile Strength at 22 %. Dried Composite showed a loss of 27.3 % compared
with the virgin material. 12.5 % Virgin GFRTPU by weight composite showed a minor
loss of 6.3 % of Tensile Strength during the testing. Similarly, Undried Recycled
GFRTPU showed a loss of 9.17 % of percent Elongation at Break. However, Dried recy-
cled GFRTPU showed a greater loss of Percent Elongation at Break, at 16.7 %. 12.5 %
Virgin GFRTPU by weight composite showed a gain of 7.6 % of Percent Elongation at
Break.
It appears that drying of the composite prior to manufacturing did not result the in reten-
tion of Tensile Strength on the recycled composite. Similarly, drying did not result in
greater retention of Percent Elongation at Break. However, the standard deviation values
calculated for Tensile Strength and Percent Elongation at Break, with the average mean
for each set of specimens selected as the boundary condition, suggest that the data ob-
tained for the Undried Recycled GFRTPU shows greater variability compared with the
Dried Recycled GFRTPU. Standard deviations for Tensile Strength and for Percent Elon-
gation at Break for the Undried Recycled GFRTPU are the highest among all material
sets investigated. Whether the drying of the composite results in a loss or gain of the
mechanical properties compared with the Dried Recycled GFRTPU remains inconclu-
sive. Further analysis is suggested.
During this investigation, it was also found that compounding the virgin composite with
the recycled one results in greater retention of mechanical properties, when comparison
is made with both Undried and Dried Recycled GFRTPU. Only a minor loss of 6.3 % of
Tensile Strength compared with the Virgin GFRTPU was observed during this investiga-
tion. A gain of 7.6 % of Percent Elongation at break was observed during the investigation
as well. However, Percent Elongation at Break for the 12.5 % Virgin GFRTPU by weight
composite exhibits smaller standard deviation than that of the Virgin GFRTPU – 0.376
vs 0.666. Whether compounding the recycled composite with the virgin one results in a
gain of Percent Elongation at Break remains inconclusive.
31
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33
APPENDICES
Appendix 1.Force vs. Elongation curves for each specimen of Undried Recycled GFRTPU plotted on a single frame of
reference.
Appendix 2. Stress vs. Strain curves for each specimen of Undried Recycled GFRTPU plotted on a single frame of
reference.
0
500
1000
1500
2000
2500
3000
3500
0 2 4 6 8 10 12
Forc
e (N
)
Elongation (mm)
Undried Recycled GFRTPU - Force vs. Elongation
Undried 1
Undried 2
Undried 3
Undried 4
Undried 5
Undried 6
Undried 7
Undried 8
Undried 9
Undried 10
0
10
20
30
40
50
60
70
80
90
0 0,02 0,04 0,06 0,08 0,1 0,12 0,14
Stre
ss (
MP
a)
Strain (%)
Undried Recycled GFRTPU - Stress vs. Strain
Undried 1
Undried 2
Undried 3
Undried 4
Undried 5
Undried 6
Undried 7
Undried 8
Undried 9
Undried 10
34
Appendix 3. Force vs. Elongation curves for each specimen of Dried Recycled GFRTPU plotted on a single frame of
reference.
Appendix 4. Stress vs. Strain curves for each specimen of Dried Recycled GFRTPU plotted on a single frame of refer-
ence.
0
500
1000
1500
2000
2500
3000
0 2 4 6 8 10
Forc
e (N
)
Elongation (mm)
Dried Recycled GFRTPU - Force vs. Elongation
Dried 1
Dried 2
Dried 3
Dried 4
Dried 5
Dried 6
Dried 7
Dried 8
Dried 9
Dried 10
0
10
20
30
40
50
60
70
0 0,02 0,04 0,06 0,08 0,1 0,12
Stre
ss (
MP
a)
Strain (%)
Dried Recycled GFRTPU- Stress vs. Strain
Dried 1
Dried 2
Dried 3
Dried 4
Dried 5
Dried 6
Dried 7
Dried 8
Dried 9
35
Appendix 5. Force vs. Elongation curves for each specimen of 12.5 % Virgin GFRTPU plotted on a single frame of
reference.
Appendix 6. Stress vs. Strain curves for each specimen of 12.5 % Virgin GFRTPU plotted on a single frame of reference.
0
500
1000
1500
2000
2500
3000
3500
0 2 4 6 8 10 12 14
Forc
e (N
)
Elongation (mm)
12.5 % Virgin GFRTPU by wt. - Force vs. Elongation
12.5 % - 1
12.5 % - 2
12.5 % - 3
12.5 % - 4
12.5 % - 5
12.5 % - 6
12.5 % - 7
12.5 % - 8
12.5 % - 9
12.5 % - 10
0
10
20
30
40
50
60
70
80
90
0 0,05 0,1 0,15
Stre
ss (
MP
a)
Strain (%)
12.5 % Virgin GFRTPU by wt. - Stress vs. Strain
12.5 % - 1
12.5 % - 2
12.5 % - 3
12.5 % - 4
12.5 % - 5
12.5 % - 6
12.5 % - 7
12.5 % - 8
12.5 % - 9
12.5 % - 10
36
Appendix 7. Force vs. Elongation curves for each specimen of Virgin GFRTPU plotted on a single frame of reference.
Appendix 8. Stress vs. Strain curves for each specimen of Virgin GFRTPU plotted on a single frame of reference.
0
500
1000
1500
2000
2500
3000
3500
4000
0 2 4 6 8 10 12 14
Forc
e (N
)
Elongation (mm)
Virgin GFRTPU + 0.09 % Masterbatch by wt. - Force vs. Elongation
Virgin 1
Virgin 2
Virgin 3
Virgin 4
Virgin 5
Virgin 6
Virgin 7
Virgin 8
Virgin 9
Virgin 10
0
10
20
30
40
50
60
70
80
90
100
0 0,02 0,04 0,06 0,08 0,1 0,12 0,14
Stre
ss (
MP
a)
Strain (%)
Virgin GFRTPU + 0.09 % Masterbatch by wt. - Stress vs. Strain
Virgin 1
Virgin 2
Virgin 3
Virgin 4
Virgin 5
Virgin 6
Virgin 7
Virgin 8
Virgin 9
Virgin 10
