(632e) Comparison of Soxhlet Extraction and Back-Flush Filtration for Removal of Homopolymer from Starch-G-Pmma Synthesized with and without Photoinitiator

Polymers have been synthesized primarily from petroleum-based products, such as styrene, acrylates, and methacrylates. Because of rising petroleum costs and increased environmental awareness, focus has shifted towards using renewable resources to create polymers. Starch is an inexpensive, natural polymer that may be modified with petroleum-based monomers to form useful copolymers. Starch is also hydrodegradable and biodegradable, which make copolymers of starch and synthetic monomers environmentally friendly.

In this research, emulsion polymerizations were initiated with a water-soluble photoinitiator, instead of typical thermal initiators. The emulsions studied include formulations of sodium dodecylbenzene sulfate, water, methyl methacrylate, starch, and Uvinul® 3048. Emulsion polymerization is advantageous because it is water based, low temperatures are easily maintained, and high molecular weight polymers can be formed without large increases in viscosity. Photopolymerization is advantageous because it is rapid and energy efficient and can be spatially and temporally controlled. In addition, initiation is independent of temperature, and polymerization can be achieved at ambient temperature. This is a more versatile method for grafting synthetic monomers to starch than previous thermal pathways because initiation is not related to temperature and the active centers are located in the micelles of the emulsion. These characteristics control side reactions and allow for high molecular weight grafts to form during this process.

Although the combination of these methods produce polymers with high grafting efficiencies, some homopolymer must still be removed. Soxhlet extraction is the traditional separation method, but it is time consuming and difficult to remove products from the cellulose thimbles. Back-flush filtration is a quick, efficient alternative for removing homopolymer from starch-g-polymer, homopolymer, and starch mixtures. The basic filtration system has two compartments above and below the filtration membrane. The filtration system uses a low head pressure, which is continuous, and high back pressure pulses to clean the filtration system. This allows for viscous fluids to be filtered without clogging the filtration membrane.

The objective of this research is to determine if grafting efficiency is improved when the hydrogen-abstraction photoinitiator is removed from the system and the starch itself acts as the initiating species. The homopolymer was separated by back-flush filtration and Soxhlet extraction. These filtration methods were compared to determine if back-flush filtration is a viable alternative for removing homopolymer from mixtures of starch-g-PMMA instead of Soxhlet extraction. Grafting efficiencies were calculated by gravimetric means, and the systems with and without photoinitiator were compared. Initial results have shown that the highest grafting efficiencies are obtained for systems in which no photoinitiator is used. In addition, the highest grafting efficiencies are obtained at shorter reaction times in these systems without photoinitiator and at longer reaction times in the system with photoinitiator. Similar separation results were found when comparing back-flush filtration to Soxhlet extraction. Therefore, back-flush filtration is a viable alternative for removing homopolymer from highly grafted systems because it is efficient and quick.

The efficiency and ease of this technique enable grafting a number of synthetic monomers to starch without resorting to high temperatures and/or pressures, and the ease of filtration with back-flush filtration makes characterization more efficient. These copolymers may be used for many different applications such as binding materials for recycled paper processing, disposable plates, thickening agents, and biodegradable plastics.