| More recently,the critical discussion about the environment preservation has led to a renewed interest concerning biodegradable polymers.Poly(butylene succinate-co-butylene terephthalate)(PBST),as a new aliphatic-aromatic copolymer,has attracted much more attention because its combination of desirable biodegradability and good mechanical properties.It is believed that PBST has broad developing prospect in industry and particularly in the field of fiber. On the basis of the studies so far available,this study was expected to give information on the heat-setting of biodegradable PBST FDY,obtained under the condition of spinning speed 2000m/min and drawing ratio 1.50.Effects of heat-setting conditions on the structure and properties of PBST fibers were analyzed.The optimum conditions of heat-setting were discussed. This study provided theory basis and practical experience for the production and application of PBST fibers.Having certain mechanical strength is the most basic requirement of textile fibers. Heat-setting,as the eventual formation process of feiber,affects the mechanical strength of fibers greatly.Heat shrinkage is a composite indicator related to the fiber forming and post-processing and is also one of the main parameters characterizing fiber properties.Structure is the basis of various polymer performances.In view of this,mechanical properties,heat shrinkage performances and structure changes of PBST fibers after heat-setting,saying in dry-heat air or wet-heat water under slack condition,in dry-heat air held taut at constant length and on Parallel Draw Machine,were systematically studied.The breaking strength and the elongation at break of the untreated fibers were 1.66cN/dtex and 34.2%.The results of the research showed that after heat-setting under slack condition,the breaking strength of PBST fibers was mainly smaller than 1.66cN/dtex and the elongation at break of PBST fibers was greater than 34.2%.In the condition of dry air heat-setting,when the PBST fibers were heat-set at the heat-setting temperature of 110℃for the heat-setting time of 0.2min, the fibers were of good tensile properties,saying the breaking strength was 1.60cN/dtex and the elongation at break was 58.3%;when the PBST fibers were heat-set at the heat-setting temperature of 110℃for the heat-setting time of 30min,the fibers were of good elastic resilience and dimensional stability,saying the elastic recovery percentage was 84.7%(at specified elongation 20%) and the remaining boiling water shrinkage was 1.29%.In the condition of wet water heat-setting,the optimum heat-setting process of PBST fibers was heat-set at the heat-setting temperature of 110℃for the heat-setting time of 1min,saying the breaking strength was 1.47cN/dtex,the elongation at break was 65.4%and the elastic recovery percentage was 85.7%(at specified elongation 20%).After heat-setting in dry-heat air held taut at constant length,the breaking strength and the elongation at break of PBST fibers were mainly greater than the untreated fibers.In the conditions of heat-set in dry-heat air held taut at constant length,the optimum heat-setting process of PBST fibers was heat-set at the heat-setting temperature of 150℃for the heat-setting time of 30min, saying the breaking strength was 1.89cN/dtex,the elongation at break was 47.4%and the elastic recovery percentage was 92.3%(at specified elongation 20%).When the PBST fibers were heat-set on Parallel Draw Machine,the optimum heat-setting process was that the heat roller temperature was 70℃,the hot plate temperature was 140℃and the draw ratio was 1.5,saying the breaking strength was 1.67cN/dtex,the elongation at break was 39.1%,the elastic recovery percentage was 90.6%(at specified elongation 7.5%) and the boiling water shrinkage was 14.0%.In addition,the effects of water on the glass transition temperature of PBST fibers were investigated by means of DSC.The experimental result showed that after the PBST fibers were heat-set in wet-heat conditions,the glass transition temperature of PBST fibers decreased to some extent,which proved the influence of moisture on the plasticizing of PBST fibers.The micro-structural changes of PBST fibers after heat-setting were also studied by using polarizing microscope and X-ray diffractometer,etc.The elastic resilience mechanism was briefly explored. The experimental results indicated that the elastic resilience of PBST fibers at specified elongation didn't quite fit the mechanism of rubber elasticity and grain size and orientation factor of grain zone were the main factors affecting the elasticity of PBST fibers.
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