Studies on the safety of polylactic acid food packaging containers and the development of PLA composite

• Main Authors: Sin-Tian Tian, 田欣恬
• Other Authors: Yih-Ming Weng
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/90467090332096169901

碩士 === 國立嘉義大學 === 食品科學系研究所(Graduate Institute of Food Science) === 98 === As the advance of techniques on biodegradable materials, polylactic acid (PLA) becomes a novel food packaging material. Lactic acid, the building unit of PLA, is converted to lactide through condensation reaction. In turn, high molecular weight PLA is obtained by ring-opening polymerization of lactides. The transition metals, with more or less toxicity, are commonly used as catalysts in the polymerization. The residues of catalysts might migrate into foods and raise safety concerns when PLA is used as food-contact packaging materials. Thus, the contents of transition metals (lead, cadmium, arsenic, tin, antimony, barium, and nickel) in PLA containers purchased from consumer markets were analysized with graphite furnace atomic absorption spectrophotometer (GFAAS). The results show that relatively high amounts of tin (0.4~16.69ppm) and nickel (20~690ppm) were detected in all PLA samples. While barium (10.81~3802ppb), arsenic (0.91~10ppb) and lead (1.25~95.28ppb) were detected in some PLA containers, cadmium (1.96~10.63ppb) and antimony (26.22~224.7ppb) were found in only few samples. Since application of PLA in food packaging is progressively increased, the stability of PLA containers depends on a variety of conditions encountered from the initial food manufacturing processes to the final consumer handling. Therefore, the stability of commercial PLA containers was tested in simulated systems. The PLA samples were soaked in distilled water or 4% acetic acid solution at room temperature, 60℃ or 95℃ for 0.5 to 24 hr. With the same soaking solutions, the heating time was between 1 to 3 min for microwave treatment. The release of lactic acid from commercial PLA containers was determined by high performance liquid chromatograph. While no lactic acid was detected when PLA was placed in both soaking solutions at room temperature, the amount of released lactic acid was increase as the temperature and soaking time increased. At the soaking conditions of 95℃ and 24 hr, the contents of lactic acid in distilled water and 4% acetic acid were 94.7mg and 227.5mg per g PLA, respectively. In the microwave treatment, the release of lactic acid was also increased as the heating time increased. After heating for 3 min, the amounts of lactic acid found in distilled water and 4% acetic acid were 0.21mg and 0.18mg per g PLA, respectively. PLA can be used as thermoplastic materials to replace plastics derived from petroleum. While the major advantage of PLA is biodegradability, the durability and brittleness need to be improved. The incorporation of chitosan with PLA to develop composite materials possessing better physical characteristics was conducted in the second part of the present study. The ratios of PLA and chitosan used for formulating composite materials were 100/0, 98/2, 96/4, 94/6, 92/8, 90/10, 80/20, 70/30, 60/40 and 50/50. Fourier transform infrared spectrometry (FTIR) was used to qualitatively analyze the composite films. The absorption peak intensity for carbonyl group (-C=O, 1748~1755cm-1) in the FT-IR chromatograph increased as the amount of PLA increased. The mechanical properties as well as the appearance of composite films were markedly influenced by the amount of chitosan.