Study On Preparation And Modification Of Straw Flour/Poly(Lactic Acid) Composite Materials

In recent years,the matrix plastic of many composites is derived from petroleum.And the composites cannot be degraded completely and pollute the environment seriously.Polylactic acid is a kind of thermoplastic biodegradable plastics that has favorable mechanical properties,processability,biodegradability and biocompatibility.Discarded to natural environment,PLA will degrade to carbon dioxide and water after hydrolysis or biodegradation.PLA/Straw flour composites have biodegradability,non-polluting,low price and good mechanical properties,et al.At present,there are many shortcomings in the molding process,moulding formula,interface compatibility,toughness,foaming of the composites.Based on the producing of straw flour/PLA composite synthesized by straw flour as filler and PLA as matrix,this paper studies on the preliminary research and provides references for the further research.The experiments are carried out by the injection molding and compression molding to prepare straw flour /PLA composites and foamed composites.Then,the optimal preparation technology,changing straw flour content to optimize the formula of preparation,the effect of PLA-g-MAH and silane coupling agent on the interfacial compatibility of composites are all studied;At the same time,effects of different toughening agents(SBS,PE,PBS)on the toughness of the composites are studied.And the effect of AC foaming agent content on the properties of foamed composites is also studied.The properties of straw flour /PLA composites and foamed composites are discussed by SEM,DSC,apparent density,mechanical properties and water absorption.(1)Straw flour /PLA composites are prepared by injection molding and compression molding.And then,the preparation processes are optimized.The experimental results indicate that the optimal injection process is 178 ?of injection temperature,50 bar of injection pressure,and 45% of injection speed;the optimal compression process is 11 min of heating time,187? of heating temperature,4 min of holding pressure time.(2)Changing straw flour contents to optimize the formula of preparation.The experimental results indicate that when adding 20% straw flour,the apparent density is the smallest and the comprehensive mechanical properties are good,respectively.And melt flow rate is decreased with the increase of straw flour.Water absorption rate is increased with the increase of straw flour content and immersion time;The crystallization temperature of pure PLA is improved and appears two times of crystallization.(3)The effect of PLA-g-MAH and silane coupling agent on the interfacial compatibility of composites is studied.The experimental results indicate that when adding 5% PLA-g-MAH,the mechanical properties and compatibility are the best and the crystallinity and heat resistance improves greatly.When adding 5% silane coupling agent,the bending strength and tensile strength are increased,the impact strength is decreased,and the interfacial bonding ability is improved,which promotes the complete crystallization.But the melting temperature is not improved.(4)The effects of different toughening agents(SBS,PE,PBS)on the toughness of the composites are studied.The experimental results indicate that mechanical properties are improved and the effect of PBS is obvious and the morphology of the samples is smooth.(5)Straw flour /PLA foamed composites are prepared by compression molding.And then,the preparation process is optimized.The experimental results indicate that the optimal compression process is 187? of heating temperature,7 MPa of holding pressure,25 s of holding pressure time.(6)The effect of AC content on the properties of foamed composites is studied.The experimental results indicate that when AC is up to 1%,apparent density is the smallest,microcellular structure are distributed uniformly,and mechanical properties are the best.Water absorption ratio of foamed WPCs is larger than that of non-foamed WPCs.