Thesis (M.Sc.)--Chulalongkorn University, 2007

Biodegradable polymers derived from renewable resources considered as natural polymeric materials have now become increasingly scientific and commercial interest. Polylactic acid is one of such biobased polymer that exhibits many properties equivalent to or better than many petroleum-based plastics; therefore, it is suitable for a variety of applications. However, the synthesis of PLA is somewhat cumbersome. Due to its high film forming property, chitosan, a natural polymer derived from crab and shrimp shell, was used to combine with low molecular weight polylactic acid (LPLA). In this research, we studied the properties of copolymer films between LPLA and chitosan with the help of crosslinking agent and the copolymer film was prepared by solution casting technique. Glutaraldehyde (GA) could effectively reduce the swelling capacity of the copolymer films, the increased GA concentration reduced the swelling capacity but increased the brittleness of copolymer films. The film prepared by grafting lactic acid on chitosan , so called CLG3 film exhibited the lowest swelling capacity of 47.02 +- 0.46 % as well as tensile strength (MPa), Young’s modulus (MPa), and % elongation at break value at 82.83 +- 0.87 MPa, 3177.57 +- 18.11 MPa, and 4.88 +- 1.12 %, respectively. While CLG5-1.0%LPLA film prepared by copolymerization of chitosan and LPLA showed the lowest swelling capacity of 103.64 +- 1.36% as well as tensile strength (MPa), Young’s modulus (MPa), and % elongation at break value at 99.46 +- 8.59 MPa, 4146.31 +- 431.97 MPa, and 5.61 +- 1.04 %, respectively. Moreover, it was found that glycerol monostearate (GMS) affected the mechanical properties of the copolymer films, resulted in a decreased trend in the tensile strength, Young’s modulus, and elongation at break.