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POLYHYDROXYALKANOATE BLENDS NONWOVEN AGRICULTURAL MULCHES in AMBIENT SOIL CONDITIONS Sathiskumar Dharmalingam University of Tennessee - Knoxville, [email protected]

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POLYHYDROXYALKANOATE BLENDS NONWOVEN AGRICULTURAL MULCHES in AMBIENT SOIL CONDITIONS Sathiskumar Dharmalingam University of Tennessee - Knoxville, Sdharmal@Utk.Edu University of Tennessee, Knoxville Trace: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 5-2014 BIODEGRADATION AND PHOTODEGRADATION OF POLYLACTIC ACID AND POLYLACTIC ACID/ POLYHYDROXYALKANOATE BLENDS NONWOVEN AGRICULTURAL MULCHES IN AMBIENT SOIL CONDITIONS Sathiskumar Dharmalingam University of Tennessee - Knoxville, [email protected] Recommended Citation Dharmalingam, Sathiskumar, "BIODEGRADATION AND PHOTODEGRADATION OF POLYLACTIC ACID AND POLYLACTIC ACID/ POLYHYDROXYALKANOATE BLENDS NONWOVEN AGRICULTURAL MULCHES IN AMBIENT SOIL CONDITIONS. " PhD diss., University of Tennessee, 2014. https://trace.tennessee.edu/utk_graddiss/2760 This Dissertation is brought to you for free and open access by the Graduate School at Trace: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of Trace: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Sathiskumar Dharmalingam entitled "BIODEGRADATION AND PHOTODEGRADATION OF POLYLACTIC ACID AND POLYLACTIC ACID/ POLYHYDROXYALKANOATE BLENDS NONWOVEN AGRICULTURAL MULCHES IN AMBIENT SOIL CONDITIONS." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Biosystems Engineering. Douglas G. Hayes, Major Professor We have read this dissertation and recommend its acceptance: Arnold M. Saxton, Jennifer M. DeBruyn, Larry C. Wadsworth Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official student records.) BIODEGRADATION AND PHOTODEGRADATION OF POLYLACTIC ACID AND POLYLACTIC ACID/ POLYHYDROXYALKANOATE BLENDS NONWOVEN AGRICULTURAL MULCHES IN AMBIENT SOIL CONDITIONS A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Sathiskumar Dharmalingam May 2014 DEDICATION I dedicate my work to my Parents. ii ACKNOWLEDGEMENTS It is a great pleasure to thank everyone who helped me write my dissertation successfully. This dissertation would not have been possible without the help, support, and patience of my principal supervisors, Drs. Douglas G. Hayes and Larry C. Wadsworth, not to mention their advices and unsurpassed knowledge on polymer chemistry and nonwoven materials. I am extremely grateful to one of my Committee members, Dr. Arnold M. Saxton, for offering invaluable suggestions in statistics and helped me in interpreting the data. I owe my sincere thankfulness to the last, but by no means least, of Committee member, Dr. Jennifer M. DeBruyn, for suggestions on statistics and microbiological aspects of this project, not to mention the thought-provoking suggestions on this dissertation. I am truly indebted and thankful to Postdoctoral Research Associate in Michigan State University, Dr. Elodie Hablot. It was particularly kind of her to offer a help in weatherometry and biodegradation experiment. I would also like to extend my thanks to Dr. Ramani Narayan, who let me use his lab for biodegradability apparatus ASTM D5338. Assistance provided by Ms. Rachel N. Dunlap was greatly appreciated. I am obliged to thank Dr. Ran Ye who supported me. Finally, my special thanks to my parents and younger brother for unequivocal moral support and encouragement throughout, as always, for which mere expression of thanks does not suffice. iii ABSTRACT Agricultural mulch films, typically made of polyethylene—derived from fossil fuels— improve crop productivity by controlling weeds and providing a microclimate. Extreme fragmentation of films imposes retrieval and disposal costs, and causes environmental problems during and after their service life. Although mulch films made of biodegradable polymers such as cellulose, (fossil fuel-based) poly (butylene adipate-co-terephthalate) and polybutylene succinate are employed in the field, the fate of biodegradation of “synthetic” additives and their impact on mechanical strength are concerns. Mulches, made of biobased polymers such as poly (lactic acid) (PLA) and PLA/ polyhydroxyalkanoate (PHA) blends, has been developed using nonwoven textile technology to address the poor mechanical properties and/or biodegradability of traditional mulch films. This dissertation focuses upon biodegradation of nonwoven mulches—spunbond (SB) and meltblown (MB)—buried in soil for 30 weeks and after exposure to simulated weathering. Soil moisture, temperature, amendments, the nonwoven processing type, color, and composition (fraction of PLA and PHA) of the mulches were evaluated in soil burial studies. The biodegradation of nonwoven mulches was characterized by the loss of tensile strength, depolymerization via hydrolysis of ester bonds and decrease of glass transition temperature, melting temperature and enthalpy of fusion. At high moisture conditions, SB mulches were recalcitrant to all the soil environmental conditions and amendments, evidenced by marginal depolymerization and insignificant loss of tensile strength. MB mulches, particularly when prepared from PLA/PHA blends, underwent the greatest (~90%) loss of tensile strength among other physico-chemical losses. Although weathered SB mulches did not undergo physico- chemical changes during simulated weathering, the rate and extent of biodegradation test under composting conditions, measured using ASTM D5338, met the compostability standard (ASTM D6400) criteria ( ≥ 60% biodegradation after 90 days). MB mulches experienced the greatest extent of biodegradation ( > 90% after 90 days via ASTM D5338) and therefore are recommended as a “Class II” material in ASTM WK 29802, the standard specification being developed for biodegradability of agricultural plastics in soil. iv TABLE OF CONTENTS CHAPTER 1 INTRODUCTION AND OBJECTIVES ............................................................................ 1 1.1 AGRICULTURAL PLASTIC MULCHES ........................................................ 2 1.2 BIODEGRADABLE MULCHES (BDMs) ........................................................ 3 1.2.1 CURRENT BDMs IN THE MARKET .......................................................... 3 1.2.2 CELLULOSE- BASED MULCHES .............................................................. 4 1.2.3 STARCH-BASED MULCHES ...................................................................... 5 1.2.4 POLY (BUTYLENE ADIPATE-CO-TEREPHTHALATE) or PBAT- BASED MULCHES ....................................................................................... 6 1.3 POLYLACTIC ACID, POLYHYDROXYALKANOATE, AND THEIR BLENDS AS POTENTIALLY VALUABLE FEEDSTOCK FOR BDMs ....... 7 1.3.1 POLYLACTIC ACID (PLA).......................................................................... 7 1.3.2 POLYHYDROXYALKANOATE (PHA) ...................................................... 8 1.3.3 PLA/PHA BLENDS AS BDMs ..................................................................... 10 1.4 OBJECTIVES ..................................................................................................... 10 1.5 ORGANIZATION OF THIS DISSERTATION .............................................. 11 CHAPTER 2 LITERATURE REVIEW ................................................................................................. 13 2.1 INTRODUCTION ............................................................................................ 14 2.2 PROCESSING OF PLA ................................................................................... 14 2.3 BLENDING AND PLASTICIZATION ........................................................... 15 2.4 NONWOVEN TECHNOLOGY....................................................................... 18 2.4.1 SPUNBONDING (SB) PROCESS ............................................................... 20 2.4.2 MELTBLOWING (MB) PROCESS ............................................................ 21 2.4.3 VARIABLES IN SPUNBOND AND MELTBLOWN, AND CHARACTERISTICS OF THE PROCESS ................................................. 23 2.4.4 COMPARISON OF PLA-BASED NONWOVENS TO CONVENTIONAL NONWOVENS ............................................................................................. 25 2.5 BIODEGRADABILITY OF PLASTICS IN SOIL .......................................... 26 2.5.1 INTRODUCTION ........................................................................................ 26 2.5.2 GENERAL MECHANISM OF PLASTIC BIODEGRADATION .............. 27 2.5.3 HYPOTHESIS: DEGRADATION OF PLA MULCHES VIA A THREE STAGE PROCESS ....................................................................................... 29 2.5.4 FORMAL DEFINITIONS OF BIODEGRADABILITY ............................. 31 2.5.5 GENERAL PRINCIPLES OF TESTING THE BIODEGRADABLE PLASTICS .................................................................................................... 32 2.6 COMPOSTABILITY AND COMPOSTING CONDITIONS OF PLASTICS 36 2.7 AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) INTERNATIONAL STANDARDS FOR BIODEGRADABILITY AND COMPOSTABILITY........................................................................................ 37 2.7.1 ASTM STANDARDS FOR BIODEGRADABILITY OF PLASTICS........ 38 v 2.7.2 ASTM TESTING METHODS USED WITHIN THE STANDARD TO DETERMINE THE BIODEGRADABILITY OF PLASTICS IN SOIL ..... 43 2.8 SOIL BURIAL STUDY 1 ...............................................................................
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