Submitted to: Polymers and the Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/20/2007
Publication Date: 11/14/2007
Citation: Ludvik, C.N., Glenn, G.M., Klamczynski, A., Wood, D.F. 2007. Cellulose fiber/bentonite clay/biodegradable thermoplastic composites. Polymers and the Environment. 15:251-257. Interpretive Summary: This paper described a process to add cellulose fiber reinforcement to biodegradable plastics. Using bentonite clay to disperse fiber gave the composites much better moisture resistance than traditional methods to disperse fiber such as using gelatinized starch. Reinforced composites with increased stiffness were produced. This technique has potential as a low cost way to make water resistant, biodegrable fiber reinforced plastics.
Technical Abstract: Adding cellulose fiber reinforcement can improve mechanical properties of biodegradable plastics, but fiber must be well dispersed to achieve any benefit. Using gelatinized starch to disperse fiber is known to be effective, but starch greatly increases the moisture sensitivity of the composites and reduces high temperature stability. To overcome these limitations, aqueous gels of sodium bentonite clay were used to disperse fiber uniformly. These clay-fiber gels were combined with powdered compostable thermoplastics and calcium carbonate filler. The composite was dried, twin-screw extruded, and injection molded to make thin parts for tensile testing. An experimental design was used to determine the effect of fiber concentration, fiber length, and clay concentration. Polybutylene adipate/terephthalate copolymer (PBAT) and 70/30 polylactic acid (PLA)/PBAT blend were the biodegradable plastics studied. The composite strength decreased compared to the thermoplastics (13 vs. 19 MPa for PBAT, 27 vs. 38 MPa for the PLA/PBAT blend). The composite elongation to break decreased compared to the thermoplastics (170% vs. 831% for PBAT, 4.9% vs. 8.7% for the PLA/PBAT blend). The modulus increased for the composites compared to the thermoplastic standards (149 vs. 61 MPa for PBAT, 1328 vs. 965 MPa for the PLA/PBAT blend). All composite samples had good water resistance.