Physical Characteristics of Sweet Potato Pulp/Polycaprolactone Blends Eun-Jung Lee, 1 Dong-Keon Kweon, 2 Bong-Kyung Koh, 3 Seung-Taik Lim 1 1 Graduate school of Biotechnology, Korea University, 5-1, Anam-dong, Sungnuk-ku, Seoul 136-701, Korea 2 Green Biotechnology Research Group, The Special Division for Human Life Technology, National Institute of Advanced Industrial Science & Technology, 1-8-31, Midorigaoka, Ikeda, Osaka, 563-8577, Japan 3 Food and Nutrition Department, Keimyung University, Daego 704-701, Korea Received 29 January 2003; accepted 12 November 2003 ABSTRACT: Sweet potato pulp (SSP) obtained as a by- product from starch extraction was blended with polycap- rolactone (PCL) to prepare a biodegradable plastic material. In the blends, PCL was used as a reinforcing agent. The SPP/PCL blends were prepared by compression-molding under high temperature and pressure, at different SPP/PCL ratios, and the mechanical properties of the molded speci- mens were tested. Matrix structure and thermal properties were measured by using a Fourier transform infrared (FTIR) spectrophotometer, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and thermogravi- metric analyzer (TGA). Mechanical properties (tensile and flexural properties) were also measured to find the most suitable ratio in a SSP/PCL blend. During compression molding of the SPP/PCL blends under high pressure and temperature, chemical reaction occurred between SPP and PCL, and thus, thermal stability and mechanical strength of the blends increased and water uptake decreased. Also, by increasing the PCL content in the blend, the matrix in the blend became more homogeneous, and consequently, me- chanical strength of the molded specimen increased. At 7/3 or 6/4 weight ratio of SSP/PCL, water uptake of the molded specimen became substantially less than that at 8/2. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 861– 866, 2004 Key words: SSP/PCL blend; sweet potato pulp; thermal characteristics; water uptake; mechanical strength INTRODUCTION Along with modern industrialization, plastic con- sumption has been increasing worldwide. The large volume of plastics, used particularly for disposables, such as packaging materials for the fast food industry, picnic tableware, and agricultural film, became a pub- lic concern because of huge environmental accumula- tion and resulting pollution. 1 The lack of degradability of plastics impacts significantly the depletion of land- fill sites, and thus, the littering problem. Because of these recent trends in solid waste management, there is great interest in biodegradable plastic products, and efforts in developing and using environmentally friendly materials have increased. Development of biodegradable plastics is considered to be one of the ultimate solutions to the environmental problem caused by the disposal of nondegradable plastic wastes. 2–5 In this respect, biodegradable materials, including polycaprolactone (PCL) and bacterial polyesters such as polyhydroxybutyrate (PHB) and polyhydroxyval- erate (PHV), were introduced as replacements for non- degradable synthetic plastics. They are biocompatible thermoplastics which may be used as commodity plastics or as specialty polymers for medical applica- tion. 6 Among these biodegradable polymers, PCL has good mechanical properties and compatibility with other polymers. 7 Up to the present, however, these biodegradable polyesters, including PCL, are not widely used because of their substantially high unit prices. 8 In contrast, starch, one of the natural biode- gradable polymers obtained from agricultural crops, is produced at a relatively low cost. 9 Unfortunately, starch, by itself, exhibits too poor mechanical proper- ties to apply in commodity plastics, although process- ing with starch may be possible. 10 To enhance the mechanical properties of starch-based products, blending or grafting with functional synthetic poly- mers is commonly exercised. 9 –18 Sweet potato pulp (SPP) is obtained as a residual by-product in large quantities during the starch ex- traction process from sweet potato. A part of the SPP is currently used as an animal feed, but most is dis- posed of into the deep sea or landfill in most Asian countries. In the present study, the feasibility of SPP as a biodegradable plastic material was examined by blending with PCL. The effect of the PCL particles as Correspondence to: S.-T. Lim (Limst1@dreamwiz.com). Contract grant sponsor: Interdisciplinary Research Pro- gram of the Agricultural R&D Promotion Center; contract grant number: 199048-2. Journal of Applied Polymer Science, Vol. 92, 861– 866 (2004) © 2004 Wiley Periodicals, Inc.