Preparation,Properties,and Degradability Properties Of Starch-Based Composite Fibers For Fishing

A staggering amount of fishing gear is discarded every year around the world.The fishing nets made of polyethylene,nylon and other non-degradable synthetic fibers are still unable to degrade after decades in the seawater environment,becoming"ghost fishing gear"and doing great harm to fishery resources and ecological environment.In order to prevent or mitigate"ghost fishing",protect Marine fishery resources and ecological environment,and realize sustainable development,the research,development and application of degradable materials for fishing gear are particularly important.Starch is a research hotspot of biodegradable materials.It has many advantages such as wide source,low cost,complete biodegradability,good thermodynamic performance and strong regeneration ability.However,the strength,modulus and other mechanical properties and water resistance of biodegradable materials made of natural starch are always worse than those of synthetic plastics,so it is difficult to be used as a kind of polymer material alone.In general,starch needs to be thermoplastic modified and then blended with other polymers for preparation.Due to the difference of structure between starch and polyethylene,the compatibility of starch and polyethylene is poor due to the direct blending modification.The reactive extrusion technique can increase the compatibility of incompatible polymer blends.In this thesis,HDPE and plasticized cassava starch were used as raw materials,and the reactive extrusion-melt spinning method was used for compatibilization modification to prepare starch-based fishing composite fibers.The influence of blending structure on the melt processing performance,fiber structure and properties of starch based composites was studied.At the same time,the effects of different degradation methods on the degradation behavior of starch based composite fibers were also studied.The results are as follows:?1?HDPE/starch composites with different blending systems were prepared by direct melting blending method.The effect of starch contents on the rheological properties,structure,thermal properties,mechanical properties and dynamic mechanical properties of HDPE/starch composites was studied.The results showed that with the increase of starch content,the melting time of HDPE/starch blending system was shortened,the torque value was decreased,the viscosity was decreased but the fluidity was increased,indicating that the introduction of starch can effectively improve the processing rheology of the blending system.Compared with pure HDPE,the cross section of HDPE/starch blending system is relatively flat,indicating that the introduction of starch improves the toughness of HDPE.The introduction of starch destroys the crystal perfection degree of HDPE,reduces its orderliness,and results in the decrease of the total crystallinity of HDPE/starch blending system.Starch is separated from HDPE,and starch particles are dispersed among the HDPE molecular chains,which weakens the interaction between the molecular chains.Starch forms micron microzone in the matrix,which is easy to form stress concentration zone,resulting in significantly reduced mechanical properties of the blending system.The introduction of starch leads to the decrease of chain segment near the HDPE crystal region and the decrease of chain segment motion activation energy.As a result,the transition peak temperature moves to low temperature.In this peak region,E'drops sharply and the rigidity and mechanical properties of HDPE/starch blend system are significantly reduced.The introduction of a certain amount of starch can improve the processing rheology and toughness of HDPE and provide a theoretical basis and technical support for the preparation of high-performance degradable starch based fishery materials.?2?HDPE/starch composites with different blending systems were prepared by direct melting blending method,and the effects of blending structure on the processing rheology,microstructure,thermal properties,mechanical properties and dynamic mechanical properties of HDPE/starch composites were studied.The results showed that the melting time,torque,viscosity and fluidity of HDPE/starch blend system decreased with the increase of starch content.This shows that the introduction of starch can effectively improve the processing rheology of the blending system.Compared with pure HDPE,the cross section of HDPE/starch blending system is relatively flat,indicating that the introduction of starch improves the toughness of HDPE.The introduction of starch destroys the crystal perfection degree of HDPE,reduces its orderliness,and results in the decrease of the total crystallinity of HDPE/starch blending system.Starch is separated from HDPE,and starch particles are dispersed among the HDPE molecular chains,which weakens the interaction between the molecular chains.Starch forms micron microzone in the matrix,which is easy to form stress concentration zone,resulting in significantly reduced mechanical properties of the blending system.The introduction of starch leads to the decrease of chain segment near the HDPE crystal region and the decrease of chain segment motion activation energy.As a result,the transition peak temperature moves to low temperature.In this peak region,E'drops sharply and the rigidity and mechanical properties of HDPE/starch blend system are significantly reduced.The introduction of a certain amount of starch can improve the processing rheology and toughness of HDPE and provide a theoretical basis and technical support for the preparation of high-performance degradable starch based fishery materials.?2?starch based fishery composite fiber was prepared by reactive extruder-melt spinning method,and the influence of blending structure on microstructure,thermal properties,dynamic mechanical properties and mechanical properties of starch based composite fiber was studied.The results showed that the section of starch matrix composite fiber was smooth after the reaction extrusion,and there was no phase separation.Starch based composite fiber of HDPE melt temperature gradually move towards low temperature,the crystallinity decreased,narrow crystallization melting peak,high alpha shift peak weakened gradually,the narrowing,random segment increased,with the increase of starch content,starch based composite fiber fracture strength decreased significantly,but the elongation at break and nodules strength retention rate increase.?3?The degradation behavior of starch based composite fibers was studied by natural soil embedding method.The degradation mechanism of starch based composite fibers was investigated by characterizing the changes of surface morphology,structure morphology,thermal properties and weight loss rate with degradation time.The results show that:after degradation for 5 months,the surface of starch based composite fiber becomes rougher,showing flocculent layering,and the internal structure of composite fiber becomes fluffy and collapses.The weight loss rates of HDPE,STR-50,STR-80and STR-90 composite fibers were 0,5.2%,29.9%and 34.8%,respectively.With the increase of starch content,the weight loss rate and degradation performance of composite fiber increased.?4?The condition of environmental aging was simulated by ultraviolet aging environment box to study the photodegradation behavior of the starch matrix composite fiber and the changes of microstructure and macroscopical properties of starch based composite fibers during photodegradation were analyzed.The results showed that after photodegradation for 1000h,the surface of the composite fiber STR-80 showed no significant difference,and the internal structure of the composite fiber showed multi-hole structure without collapse,and the weight loss rates of HDPE,str-50,str-80and str-90 were 0.98%,3.21%,5.51%and 8.12%,respectively,indicating that the photodegradation degree of starch matrix composite fiber was low.The breaking strengths of STR-50 and STR-80 were 9.42 c N.tex^-1 and 3.44 c N.tex^-1,respectively.STR-90 had little fiber strength.The loss rates of breaking strength were 71.7%,70.5%and 100%,respectively.The relationship between the breaking strength and the loss rate of the breaking strength and the photodegradation time of the composite fiber tends to be linear,and the breaking strength decreases significantly with the increase of the photodegradation time.