Fabricating Biodegradable Mulches

Douglas G. Hayes

1, Larry C. Wadsworth 1, and Karen K. Leonas 2

Department of Biosystems Engineering and Soil Science,University of TennesseeKnoxville, TN USA 37996-45312

Department of Apparel, Merchandising, Design & Textiles, Washington State UniversityPullman, WA 99164-2020,

dhayes1@utk.edu

ASHS Conference, 31 July 20121

Plastic Agricultural Mulches

Started in the 1950s

Its cost (~240 USD / ha) offset by increased crop yield

2.6 million metric tonnes of plastic mulches / yr

10 million ha of land used in China alone (80% of world market)

Plastic Agricultural Mulches: Advantages

Reduced weed problems

Enhanced moisture control

Increased soil temperature

extension of growing season

increased plant growth rate

Reduced soil compaction

Reduced fertilizer leaching

Cleaner product

Root pruning eliminated

http://www.ces.ncsu.edu/depts/hort/hil/hil-33.htmlASHS Conference, 31 July 20123

“Plastic”

Agricultural Mulches: Disadvantages

Potential environmental hazard: black plastic (polyethylene, “PE”)

slowly biodegradable or compostable

Harmful biodegradation products

Becomes brittle debris can tarnish crops; affect drainage of water; increase local pesticide / toxicant levels

petroleum-derived poor sustainability

Costly and laborious to remove (250 USD / ha)

Greater initial costs

Intensive irrigation management

Soil erosion (between strips)ASHS Conference, 31 July 20124

Developed in the 1980’s

Ultimate goal: complete biodegradation at the end of the cultivation season, after being tilled into the soil

“.. the best choice appears to be a mulch material ..

with an outdoor service life which matches the crop duration, and

which would later be incorporated by the agricultural system”

(Martin-Closas, et al Biopolymers 2011, 277-299.)

High cost compared to conventional PE mulches, 2.54 x

Organic agriculture: regulations differ between countries and states, affecting product use

Development of standards is challenging! long-term degradation processes that differ greatly with ecosystem & climate

Biodegradable Mulches

Molecular Structure of Polymers Employed in Agricultural Mulches

Paper Mulching

Used extensively prior to 1950 (Shogren, R. L. J. Sustain. Agric. 2000, 16, 33-47)

Are readily biodegradable (Shogren, R. L. J. Sustain. Agric. 2000, 16, 33-47)

Possess greater puncture resistance than plastic mulches

High weight & easily embrittled difficult to lay down in the field

Susceptible to tearing from the wind

Rapidly lose mechanical strength when wet

Commercially Available Polymers and Blends Employed in Biodegradable Agricultural Mulches

Product Name Polymer Manufacturer

Biocycle® Sucrose / PHA blend PHB Industrial (Brazil)

Bio-Flex PLA / copolyester FKUR, Willich (Germany)

Biomax TPS Starch DuPont (USA)

Biomer L PHA Biomer (Germany)

Bionolle PBS Showa High Polymer (Japan)

Biopar Starch co-polyester Biop (Germany)

BiosafeTM PBAT/starch blend; PBS; PBSA

Xinfu Pharmaceutical Co (China)

Eastar BioTM PBAT / starch blend Novamont (Italy)

Eco-Flex® PBAT / starch blend BASF (Germany)

Ecovio Ecoflex®

+ PLA BASF (Germany)

Envio Ecoflex®

+PLA+starch blend BASF (Germany)

Green = Biobased

Product Name Polymer Manufacturer

EnPol PBS IRE Chemical (Korea)

GreenBio PHA Tianjin GreenBio Materials (China)

Ingeo® Starch + PLA; PBS + PLA Natureworks (USA)

Mater-Bi® PCL + starch blend Novamont (Italy)

Mirel® PHA Metabolix (USA)

Paragon Starch + thermoplastic starch Avebe, (Netherlands

ReNew PHA Danimer Scientific (USA)

Skygreen® Terephthalic acid co-

polyester

SK Chemicals (Korea)

Commercially Available Polymers and Blends Employed in Biodegradable Agricultural Mulches

Green = Biobased

PBAT (Ecoflex®)

Mechanical properties similar to PE (high flexibility, good impact strength, and good melt processability)

Biodegradable under composting environments (55-58 oC)

Readily forms composites with cellulose, polysaccharides, PLA, and PHA

Field trials: mulches performed similarly to PE mulches: weed control and crop yield; slighly higher soil temperature (Ngouajio, et al., HortTechnol. 2008, 18, 605-610)

Undergoes photodegradation depolymerization & cross-link formation reduced extent of biodegradation (Kijchavengkul, et. al., Polym. Degrad. Stab. 2010, 95, 99-107)

Not biobased (“synthetic”)

Mater-Bi®

“is nowadays amongst the best developed products”

(Martin-Closas &Pelacho, Biopolymers 2011, 277-299)

Possible concern: weakness / susceptibility to tearing in the transverse direction (Briassoulis, Polym. Degrad. Stab. 2006, 91, 1256-127)

Not biobased (“synthetic”)

PLA: Advantages

Biobased

Readily available

140,000 metric tonnes at the Blair, NE USA facility operated by NatureWorks, LLC

Global production: 800,000 metric tonnes by 2020

Reasonably priced 2.1 USD / kg

Compostable

Possesses good mechanical strength

PLA: Disadvantages

Hard embrittlement & poor thermostability

Highly crystalline

Hydrophobic

A “synthetic”

(produced via chemical catalysis of biobased lactic acid)

slowly biodegrades under ambient conditions in soil (Tokiwa, et al. Int. J. Mol. Sci. 2009, 10, 3722-3742)

Enriched microbial community nearly complete disintegration of PLA in soil at 30oC (Hakkarainen et al. Polymer 1999, 41, 2331-2338)

Blends formed (PBAT, PCL, and common plasticizers such as lactic acid, glycerol, and citrate esters)

Nonwovens Textiles

(Wikipedia) “fabric-like material made from long fibres, bonded together by chemical, mechanical, heat or solvent treatment”

“manufactured sheet, web or bat of directionally or randomly oriented fibers, bonded by friction, and/or cohesion and/or adhesion”

(http://web.utk.edu/~mse/Textiles/)

Not woven or knitted; not paper-based

Examples: Medical surgical gowns; HEPA air filters, disposable clothing

Nonwovens as Mulches?

Nonwovens: high strength, low weight

Nonwovens: small fiber size Increased rate of hydrolysis

Nonwovens can be made inexpensively

crystalline morphology, often

SB-PLA: 14.8 ±

MB-PLA: 6.3 ±

Ultimate Goal

Prepare a biobased agricultural mulch

.. that will perform well for specialty crop cultivation

.. that would undergo slow deterioration during the cultivation season (~March – October)

.. that would be tilled into the soil at the end of the cultivation season (~November)

.. and would be completely mineralized by the beginning of the next cultivation season (March)

Alternate Goal:

..would not undergo fragmentation during a long cultivation season

.. would be easily retrieved from the soil at the end of the growing season

.. then would be composted ASHS Conference, 31 July 201216

Conceptual Model for

Biodegradation of Mulches

Assessment Tools1.

Soil burial studies in greenhouse experiments

Utilization of mulches for cultivation of vegetables in high tunnel and open field studies

Weatherometry and biodegradability testing

10 weeks

Greenhouse Study IDeterioration of MB-PLA-10 Mulch: Lime Treatment

29 weeksWadsworth et al, submitted (2011)

Evidence of Deterioration for MB-PLA-2010 Mulch:SEM Analysis (Greenhouse Study I)

Lime soil treatment29 weeks exposure

ASHS Conference, 31 July 201220 Wadsworth et al, submitted (2011)

Deterioration of MB-PLA-10 Mulch (Greenhouse Study I)

Measurement Method 0 wk 10 wk, Control

10 wk, Lime

Mass, g m-2 ASTM D3776 82.58 ±

8.35 97.71 ±

7.57 96.66 ±

Thickness, mm ASTM D1777 0.435 ±

0.020 0.666 ±

0.109 0.679 ±

Air Permeability, cm3

s cm-2

ASTM D737 37.0 ±

2.1 56.2 ±

17.4 Not Tested

Breaking Load, N ASTM D4632 6.87 ±

3.26 2.05 ±

1.26 0.88 ±

Breaking Elongation ASTM D5035 5.98 ±

3.67 4.16 ±

3.20 3.82 ±

, kDa GPC 93.5 ±

0.620 111±

8 112 ±

ASHS Conference, 31 July 201221Wadsworth et al, submitted (2011)

Effect of Soil Moisture and Pineapple Juice: FTIR Analysis (Greenhouse Study II)

MB-PLA (85%) / PHA (15%)

30 wk of soil burial

High Moisture and Enzymes (Bromolain) enhance hydrolysis

High Tunnel and Open Field Studies in TN, TX, and WA: Mulches (2010)

BioBag (BioAgri, Mater-Bi®-Based),

Palm Harbor, FL

BioTelo, (Mater-Bi®-Based), Dubois Agrinovation, Waterford, Ontario

SB-PLA-2010-white, PLA donated by NatureWorks, Blair NE USA; made at Saxon Textile Institute (STFI), Germany, white, 90 g m-2

Black Plastic Polyethylene, Pliant Corp, Schaumburg, IL

Cellulose Control,

“WeedGuardPlus,”

SunShine Paper Company, LLC, Denver, CO USA, 107 g m-2

Control

(no mulch)ASHS Conference, 31 July 201223

High Tunnels at Univ. Tennessee

Maximum Load –

Machine Direction for Mulches as Received

Comparison of Locations/Environment

Percent of Maximum Load at Time 3

Open Field High Tunnel ASHS Conference, 31 July 201226

Biodegradability and Weatherometry

Photodegradation of PLA: Norrish II mechanism of carbonyl polyester (Ikada E. , J Photopolym Sci Technol 1997:10(2):265-

Weatherometry Treatment

Summary

Conventional polyethylene mulches: the environmental fate at end-of-life is a major concern

Commercially available biodegradable mulches:

Many perform well (mechanical strength, biodegradability under specific conditions); but:

Are they applicable to all cultivation systems, climates, and soil types?

Are they truly environmentally benign under all circumstances?

Can they meet organic agriculture certifications?

Have they been sufficiently tested in large-scale agriculture to ensure environmental safety?

What will “third generation”

biodegradable mulches look like? (Can improved performance be commensurate with reduced cost?)

Summary

Greenhouse Studies

Meltblown-PLA / PHA in the presence of lime and/or compost shows the greatest extent of deterioration

Spunbond-PLA: excellent properties for long-use compostable material

Long-Term High Tunnel & Open Field Studies

Loss of mechanical strength: most visible parameter for assessment of physico-chemical changes

No universal trend based on mulch type and location

Biodegradable Mulches for Specialty Crops Produced Under Protective Covers

Debra Inglis and Carol Miles (Project Directors)1;Andrew Corbin, Ana Espinola‐Arredondo, Annabel Kirschner, Karen Leonas, Tom Marsh and Tom Walters1;

Doug Hayes, Bobby Jones, Jaehoon Lee, Larry Wadsworth and Annette Wszelaki2; Jennifer Moore‐Kucera3; Russ Wallace4; Marion Brodhagen5 ; and Eric Belasco6;

NatureWorks (PLA Donation)Saxon Textile Institute (Germany)

Biax Fiberfilm (WI USA)S. Dharmalingam , C. Tyler Pannel and R. Dunlap (UTK), Dr. William Klingeman, Phil Flanagan

SCRI Grant Award No. 2009-51181-05897

Hayes et al, Biodegradable Agricultural Mulches Derived from Biopolymers, in Degradable Polymers and Materials, Principles and Practice, 2nd Edition (ACS Symposium Series), in press.

Back-Up Slides

Important Definitions

Biobased: “.. composed in whole or in significant part of biological products or renewable domestic agricultural materials (http://www.biobased.us/)

Compostable plastic: “.. undergoes degradation by biological processes during composting to yield carbon dioxide, water, inorganic compounds, and biomass .. leaves no visible, distinguishable, or toxic residue”

(ASTM D6400)

Biodegradable plastic: “..degradation (change in its chemical structure) resulting from the action of naturally occurring microorganisms such as bacteria, fungi, and algae”

(ASTM D6400)

Biobased: “.. composed in whole or in significant part of biological products or renewable domestic agricultural materials (http://www.biobased.us/)

Compostable plastic: “.. undergoes degradation by biological processes during composting to yield carbon dioxide, water, inorganic compounds, and biomass .. leaves no visible, distinguishable, or toxic residue”

(ASTM D6400)

Biodegradable plastic: “..degradation (change in its chemical structure) resulting from the action of naturally occurring microorganisms such as bacteria, fungi, and algae”

(ASTM D6400)

Organic Agriculture:

“An ecological production management system that

promotes and enhances biodiversity, biological cycles, and soil biological activity .

.based on minimal use of off-farm inputs and

on management practices that restore, maintain, or enhance ecological harmony”

(USDA-NOSB)

Synthetic Material:

“A substance that is formulated or manufactured by a chemical process

or by a process that chemically changes a substance .. from a naturally occurring plant, animal, or mineral sources..”

(USDA-NOSB)

Sustainable Agriculture:

“Integrated system of plant and animal production practices that will, over the long term:

satisfy human food and fiber needs;

enhance environmental quality and the natural resource base upon which the agricultural economy depends;

make the most efficient use of nonrenewable resources and on-farm resources ..

sustain the economic viability of farm operations;

and enhance the quality of life for farmers and society as a whole. “

(1990 USA Farm Bill)

Outline1.

Introduction, Goals, and Approaches

Soil burial / greenhouse studies

Performance assessment in high tunnel and open field studies

Weatherometry and biodegradability testing

Conclusions

Key Scientific Advisors and Stakeholders

John Dorgan, Site Director, Colorado Center for Biofuels and Biorefining (C2B2), Department of Chemical Engineering; Colorado School of Mines, Golden, CO

Ramani Narayan, Department of Chemical Engineering and Materials Science; Michigan State University, 2527 Engineering Building, East Lansing, MI

Robert Green, NatureWorks LLC, 402 Sir Walker Lane, Cary, NC

Terry Phillips, Mark Williams, BioBag USA, Palm Harbor, FL

Several members of the Specialty Crops Growers / Organic Farming Community of TN, TX, and WA

Comparison of Locations/Environment

Percent of Maximum Elongation at Time 3

Open Field High Tunnel ASHS Conference, 31 July 201239

Comparison of Open Field & High Tunnel

Percent of Maximum Elongation at Time 3

Goals for Biodegradable Mulches in Agriculture Current NIFA-SCRI Project: Oct 1, 2009 –

Sept 30, 2012

To assess agricultural, ecological, and economic consequences of using biodegradable mulches in protected (High Tunnel, or HT) and Open Field (OF) specialty crop production systems.

To test Poly(Lactic Acid)-

[PLA-] based nonwovens (Spunbond and Meltblown) as mulch prototypes.

To test PLA and commercial “biodegradable” mulches for their performance in growing tomatoes

under HT and OF conditions at 3 different US sites .. in a controlled study

Provide data that may be useful for developing a standard for biodegradation of mulches

Sites for Investigation

Washington State University, Mount Vernon and Pullman Campuses

Texas A&M / Texas Tech University, Lubbock, TX

University of Tennessee, Knoxville, TN

SCRI Interdisciplinary Research Team

Materials Working Group, “WG”

(UTK, WSU)

Design new biodegradable mulches from PLA and its biopolymer blends via nonwovens textile technology

Physico-Chemical Testing

Crops WG (WSU, UTK, TAMU/TTU)

Assess use of biodegradable mulches in high tunnels for specialty crop production systems: plant physiology, weeds, pests, and diseases

Outreach to specialty crop growers/ organic farming community

SCRI Interdisciplinary Research Team

Soils WG (WSU, UTK, TAMU)

Assess the impact of biodegradable mulches on soil ecosystem

Economics WG (WSU, TTU)

Assess the economic impact of using biodegradable mulches in high tunnels

Sociology WG (WSU, UTK)

Better understand the needs and concerns of the specialty crops growers / organic farming community,

Discover and address the barriers hindering increased use of biodegradable mulches and high tunnels ASHS Conference, 31 July 201244

Nonwovens Textiles: Spunbond (SB)

Thermoplastic polymers are melted;

extruded through spinnerets;

fibers are cooled and collected on a conveyer belt

ASHS Conference, 31 July 201245 http://web.utk.edu/~mse/Textiles/

Nonwovens Textiles: Meltblown (MB)

Low viscosity polymers are melted and extruded from a spinneret;

A stream of high velocity hot air disperses and solidifies the extruded polymer

ASHS Conference, 31 July 201246http://web.utk.edu/~mse/Textiles/

Biobased; not “synthetic”

Readily available

60,000 tonnes per year

High cost

Readily biodegradable, including in soil

Highly crystalline thermoplastic polymer susceptible to embrittlement & thermal

degradation

Incompatible with several other polymers

Susceptible to loss of elongation at break due to ultraviolet radiation produced by the sun

Greenhouse Study I (UTK)

3 Mulches

“Spunbond”

= SB-PLA-2010-white

“Meltblown”

= MB-PLA-2010-white,

Cellulosic (WeedGuardPlus)

3 Soil treatments (manure, lime, control)

2 Durations (10 wk, 29 wk)

3 Replicates

Mulches buried 2 cm below the soil surface

Soil from a certified organic farm

1.0 L of water per tray per 48 h period

ASHS Conference, 31 July 201248 Wadsworth et al, submitted (2011)

PLA Nonwoven Mulches (SEM Micrographs)Molecular Weight:SP-PLA-2010: Mn

= 132,000; PDI = 1.5MB-PLA-2010: Mn

= 111,000, PDI = 1.5

Cellulose: 20.8 ±

SB-PLA: 14.8 ±

MB-PLA: 6.3 ±

Wadsworth et al, submitted (2011)

Greenhouse Study II: Effect of Moisture Level

Mulch and Treatment Breaking Load, gSB-PLA-11, as received 4190 ±

148High Moisture 3820 ±

315Low Moisture 4200 ±

145MB-100% PLA-11, as received 1820 ±

299High Moisture 639 ±

168Low Moisture 587 ±

222MB 75% PLA/25% PHB-11 513. ±

252High Moisture 89.4 ±

45.8Low Moisture 70.0 ±

• Low and High Moisture: 1.0 L and 0.5 L per tray per 48 h, respectively• Soil from organic farm with compost added• Burial in soil for 10 wk• 3 replicates

Mulches for High Tunnel and Open Field Studies

High Tunnel and Open Field Studies in TN, TX, and WA (2010): Methods and Conditions

Mulches laid 14 ft long, 2-3 ft wide and 5-6 ft apart in high tunnels or open fields

Tomatoes planted: ~April –

September, 2010

Irrigated: 1 inch of water per week

Continuous monitoring of soil & air temperature, moisture, pests & diseases, etc.

Several different physical and chemical test conducted on retrieved mulches

High Tunnels at WSU-Mount Vernon

High Tunnel and Open Field Studies (2010): Decrease of MW

Biobag BioTelo

SB-PLA

Greatest loss of MW occurs for High Tunnel, TN (thus far)

Loss of MW: Biobag > Biotelo >

Comparison of Open Field & High Tunnel

Percent of Maximum Load at Time 3

Comparison of Open Field & High TunnelPercent of Maximum Elongation

Outline1. Introduction, Goals, and Approaches2. Soil burial / greenhouse studies3. Performance assessment in high tunnel and open field studies4.

Weatherometry and biodegradability testing5. Conclusions

Key Participants1.

Dr. Elodie Hablot, Prof. Ramani Naryan, and his group, Michigan State Univ, East Lansing, MI USA

S. Dharmalingham, Drs. Doug Hayes and Larry Wadsworth, UTK

Preliminary Results: Weatherometry (GPC Analysis)

2-fold decrease of Mn for all mulches; polydispersity index increases

SB-PLA-

white MB PLA MB-PLA+PHA

Mn (g/mol)0 day 39000 44000 44000 3100021 days 17928 18430 20701 14045Mn 0d

/Mn 21 d 2.18 2.39 2.13 2.21

Mw (g/mol)

0 day 52000 56000 56000 4300021 days 42299 46834 48309 32451Mw 0d

/Mw 21 d 1.23 1.20 1.16 1.33

PDI0 day 1.33 1.27 1.27 1.3921 days 2.36 2.54 2.33 2.31PDI 0

21 d 0.56 0.50 0.54 0.60

Preliminary Results: Weatherometry (GPC Analysis)

0 5 10 15 20 25Ageing (days)

BSBWSBMB PLAPLA/PHB

Preliminary Results: Weatherometry (Differential Scanning Calorimetry, DSC)

For all 100% PLA nonwovens, two melting peaks occurred after ageing different type and/or size of crystalline zones

From lowest to highest degradation): MB PLA > SB- PLA-2011-black > SB-PLA-2011-white > MB PLA/PHA

Mulch Tg

(°C) Tm

(°C) ∆Hm

(J/g)SB-PLA-black –

Day 0 62 168 51.9SB-PLA-black –

Day 21 59 (-5%) 150 / 159 (-10%/-5%) 38.0 (-27%)SB-PLA-white –

Day 0 62 169 45.8SB-PLA-white –

Day 21 60 (-3%) 155 / 162 (-8%/-4%) 39.2 (-14%)MB PLA –

Day 0 62 168 47.6MB PLA –

Day 21 57 (-8%) 146 / 154 (-13%/-8%) 33.6 (-29%)MB -

PLA/PHB –

Day 0 41 140 / 166 0.8 / 43.2MB -

PLA/PHB –

Day 21 40 (-2%) 142 / 164 (+1%/-1%) 0.6 / 44.4 (-25%/+3%)

Preliminary Results: Weatherometry (Differential Scanning Calorimetry, DSC)

61.51°C(I)

58.83°C

62.26°C

102.11°C

92.95°C29.54J/g

167.90°C

162.58°C47.56J/g

56.69°C(I)53.73°C

58.02°C

112.50°C

102.84°C32.41J/g

153.87°C

148.19°C33.60J/g

146.17°C

0 50 100 150 200 250

Temperature (°C)

MBPLA-0d.001––––––– MBPLA-21d.001–––––––

Exo Up Universal V4.3A TA Instruments

Preliminary Results: Weatherometry (FTIR) (SB-PLA-2011-black)

1900210023002500270029003100330035003700Wavenumber (cm-1)

Day 0Day 21

Hydroperoxidesand alcohols

1900210023002500270029003100330035003700Wavenumber (cm-1)

Day 0Day 21

Hydroperoxidesand alcohols

Four mulches investigated

Spunbond PLA 2011 –

Meltblown PLA 2011 (white)

Meltblown 75% PLA / 25% polyhydroxyalkanoate (PHA)

All mulches treated by weatherometry

Ci4000 Xenon Weather-Ometer,

Standard = ASTM G155-05a

Exposure Cycle: 102 min light at 63°C; 18 min light and water spray Exposure time: 21 d (504 h)

Irradiance: 0.35 W m-2

Wavelength: 340 nm

All mulches analyzed for biodegradability (ASTM D5833), before and after weatherometry treatment

Ongoing Research

Greenhouse Studies

Focus upon moisture level, use of enzymes, new PLA/poly(hydroxyalkanoate nonwovens (lower MW)

High Tunnel & Open Field Studies

New Spunbond PLA mulch; Year 2 study is ongoing

All mulches underwent deterioration via weatherometry; biodegradability testing is ongoing

Fabricating Biodegradable Mulches

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