Recipient Organization
UNIV OF NORTH DAKOTA
(N/A)
GRAND FORKS,ND 58201
Performing Department
(N/A)
Non Technical Summary
This proposal seeks to improve our ability to utilize agricultural crops by developing and evaluating improved bio-based, biodegradable polymers suitable for a wide range of applications. Improved, cost effective bio-based polymers will play an increasingly large role in the agricultural economy. In addition, there are currently over 70 billion tons of resin produced annually in the US, with the vast majority of these polymers synthesized from petroleum. These polymers are non-biodegradable, are often difficult to recycle, and compose a significant fraction of landfill waste. Traditional bio-based, biodegradable polymers have not seen widespread application due to their lack of impact resistance. Biodegradable polymers have the potential to reduce our dependence on foreign oil while reducing the amount of solid waste entering our landfills. The primary focus of this proposal is research leading to the synthesis and characterization of a new class of largely
biodegradable polymers with greatly improved impact properties. This will be accomplished by synthesizing novel polymers with both rubbery and plastic regions on their molecules. The rubbery portions will form molecular "shock absorbers" which will absorb, and disperse, the energy of impacts. By synthesizing this copolymer the PI hopes to address three main goals: a) Produce a class of PLA copolymers with excellent impact properties. b) The copolymers must be largely (80 - 90 percent) biodegradable. c) Provide an additional, value added market for agriculture products.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
The PI proposes to improve the ability to utilize agricultural crops by developing and evaluating improved bio-based, biodegradable polymers suitable for a wide range of applications including food packaging. The primary focus of this proposal is research leading to the synthesis and characterization of a new class of largely biodegradable polymers with greatly improved impact properties. This will be accomplished by synthesizing novel poly(ethylene-propylene-rubber)-graft-polylactide copolymers. The ethylene-propylene-rubber (EPR) and polylactide (PLA) components should form a two-phase system with very small EPR domains finely dispersed in a hard PLA matrix. The first objective of this work is to synthesize a new class of substantially biodegradable polymers. PLA is derived from carbohydrate rich crops, and can be quickly and efficiently degraded to carbon dioxide and water. Unfortunately, PLA has several properties which prohibit its wide spread application. The
most significant problem is the brittle behavior of PLA under loads, which limits its applications to those that do not require high impact resistance. The main method of impact modification is to blend the polymer with rubber. The resultant blend forms a two-phase system with rubbery particles dispersed in a hard, brittle plastic matrix. The rubbery phases absorb kinetic energy, resulting in large increases in impact toughness with only limited decreases in strength. This method is limited due to the low degree of interfacial adhesion and the formation of large, poorly dispersed rubber phases due to the incompatibility of PLA and most rubbery polymers. This work will produce a new type of impact modified PLA via the synthesis of a novel graft copolymer composed of ethylene-propylene-rubber (EPR) with PLA side chains. EPR was chosen because of its excellent modification properties and because it is certified for food contacting applications. In the proposed polymer the PLA branches
are linked directly to the EPR main chain. The PI theorizes that these linkages will prevent the chemically dissimilar EPR from agglomerating into large phase domains. Therefore, the resultant graft copolymer will be composed of a series of very small EPR phases finely dispersed within the hard PLA matrix. The chemical bonds between the EPR and PLA will further serve to enhance the interfacial adhesion between the phases. This will allow stresses to be efficiently transported from the brittle PLA phase to the rubbery EPR phase. The second major objective of this proposal is to optimize the mechanical and degradation properties of the EPR-PLA graft copolymer. A systematic study will be conducted to determine the effects of the molecular architecture on the mechanical and degradation properties of the graft copolymer. Important macromonomer variables that will be studied include the EPR molecular weight, weight percent of propylene, and the concentration of branch points. PLA variables
include the molecular weight of the individual branches and the weight percent of EPR in the final polymer blend. These results will be used to design polymers with targeted properties.
Project Methods
The formation of the impact modified Polylactide (PLA) will be accomplished via a two-stage polymerization. Stage 1 The first step involves the production of rubbery ethylene-propylene-rubber (EPR) macromonomers with controlled levels of hydroxyl groups incorporated into the main chain. The PI proposes to produce EPR macromonomers using a single site type catalyst with methyl aluminoxane (MAO) as a cocatalyst. The hydroxyl groups will be incorporated into the EPR via a terpolymerization of ethylene, propylene, and 5-hexen-1-ol. A systematic study will be conducted to determine the effects of EPR molecular weight, propylene content, and hydroxyl incorporation on the mechanical and degradation properties of the final copolymer. The propylene content will be varied from 20 to 70 weight percent. This will provide impact modifiers that range from crystalline and display plastic characteristics at low propylene incorporation to almost totally amorphous polymers at high
propylene incorporation levels. The concentration of hydroxyl groups incorporated into the EPR will determine the number of PLA chains grafted onto the polymer backbone. The hydroxyl concentration will range from 1 to 10 hydroxyl groups per 1000 carbons in the EPR chain. Finally, the molecular weight of the EPR macromonomer will be varied from 10,000 to 100,000 g/mol. Stage 2 The hydroxyl modified EPR macromonomers produced in Stage 2 will be mixed with L-lactide. The L-lactide will subsequently be polymerized via a melt polymerization catalyzed by tin octanoate. The hydroxyl groups on the EPR main chain will serve as initiation sites for the formation of PLA. The resultant copolymer will be composed of EPR main chains with PLA branching. The number of PLA branches will be determined by the hydroxyl concentration on the EPR chain while the molecular weight of the PLA branches will be controlled by adjusting the stoichiometry of the L-lactide feed. The PLA branches will be synthesized
with molecular weights ranging from 30,000 to 60,000 grams per mole. The resultant polymer blend should phase separate due to the incompatibility of PLA and EPR, with very small rubbery EPR phases finely distributed in a PLA matrix. This polymer mixture should exhibit superior impact properties to PLA and PLA modified with traditional rubber blends. This polymer system contains no leachables and will still be eligible for food contacting applications. The second major goal of this proposal is to conduct a systematic study on the mechanical and degradation properties of the polymer systems produced in this work. This research will determine the influence of the molecular architecture of the graft copolymer on the resultant mechanical characteristics. Variables that will be measured include the notched Izod toughness, Young's modulus, loss modulus, and storage modulus. The degradation kinetics will also be studied to determine the effect of EPR modification. These results will be used
to synthesize custom polymers with targeted properties.