Emulsion Photopolymerization of Synthetic Monomers onto Corn Starch

Grant# 03-02
Principal Investigator: Julie Jessop
Student Support: Chris Comer & Nayeon
Organization: Department of Chemical and Biochemical Engineering, The University of Iowa
Technical Area: Renewable Energy

Public Abstract
Corn starch is a biodegradable, renewable polymer that can be combined with synthetic monomers to reduce cost and improve physical properties. Traditional copolymerization methods involve thermal activation of a redox initiator such as ceric ammonium nitrate to form a free radical active center on the starch to which synthetic monomer may be grafted. The resulting graft copolymers find industrial applications as plastics, adhesives, composites, fillers, and sizing. This project seeks to develop a novel method to produce these graft copolymers by combining photoinitiation and emulsion polymerization techniques. Emulsion polymerization will reduce homopolymerization side reactions and provide more control of system temperature and viscosity. Photopolymerizations use less energy than thermal reactions and depend on light rather than heat to start the reaction. Thus, the photografting reaction can be decoupled from the thermal processing of the corn starch (e.g., gelatinization). This project addresses the mission of the Iowa Energy Center by investigating a means to add value to a renewable resource using a more energy efficient method.

The overall goal of this research is to improve the physical properties of grafted corn starch and to increase the grafting percent of synthetic monomers using emulsion photopolymerization. This goal will be accomplished by:

1. Grafting synthetic monomers onto corn starch using emulsion photopolymerization;
2. Obtaining kinetic information and grafting percent from the photografting of synthetic monomers onto corn starch;
3. Determining physical properties of the grafted polymer systems;
4. Presenting these research results to the greater scientific community.

Raman scattering measurements will enable a thorough investigation of the reaction kinetics and system composition. The grafting of acrylic monomers onto corn starch will be monitored in real time using Raman spectroscopy. In-situ characterization of the starch surface before and after grafting using Raman microscopy will provide a measure of the concentration and distribution of the acrylic grafts on the starch. The starch surface will be viewed using scanning electron microscopy before and after grafting to determine changes in morphology. The thermal and mechanical properties of the grafted corn starch will be investigated using differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Results from this research will be communicated to the scientific community through publications and presentations, as well as through incorporation in polymer science classes at the undergraduate and graduate levels.

Work to Date (Technical Report – April 2007)
This progress report focuses the determination of the molecular weight of the polymer grafts and homopolymer using GPC. As in prior reports, general emulsion formulations are included in the appendix as well as a list of all samples GPC was performed on.

As previously shown, differences in grafting efficiency were observed with increasing illumination times in starch samples grafted with and without photoinitiators. The samples were prepared as discussed in previous reports and the molecular weight (Mw and Mn) and the PDI were calculated based on polystyrene standards. The molecular weights shown here are a combination of homopolymer and grafted polymer chains. The polymer chains were cleaved from the starch through hydrolysis in acetic acid and water.
Molecular Weight Comparisons Amylopectin-g-MMA with and without Photoinitiator and a comparison of High Amylose-g-PMMA vs. Amylopectin Starch-g-PMMA at varying illumination times was performed.

GPC data indicate two things that may be occurring. First, as irradiation time is increased polymer chains grafted to the starch particle may be cleaving. Second, starch degrades as it is irradiated with UV light and any residual monomer left in these systems may be initiated by the radicals formed from the cleaved starch particles. This creates a broader distribution of molecular weights, indicated by high PDIs.