Preparation And Properties Of Poly (Lactic Acid)/Calcium Carbonate Whisker Composites With Fully Degradable High Modulus

Polylactic acid?PLA?is a fully biodegradable material which has good physical and mechanical properties,and can be processed by conventional plastics processing.It has found a wide range of application in packaging,biological medicine,textiles,disposable utensils,construction and building,and 3D printing.However,the mechanical properties of PLA is still insufficient for many applications.Through adding carbon fibers or glass fibers the PLA composites with high strength and modulus can be obtained.But these composites has poor biodegradability for the non degradability of carbon fibers and the carcinogenicity of glass fibers.Calcium carbonate whisker?CCW?is a inorganic whisker filler which has a needle structure,high strength and modulus,wide sources of raw materials.Compared with carbon fibers and glass fibers,calcium carbonate whiskers has the advantages that low cost,non-toxic,completely degradable,good biological activity and so on.However,it is difficult to prepared the calcium carbonate whiskers both with large length and aspect ratio.The breaking of calcium carbonate whiskers easy occur and the orientation of the whisker is hard to control during conventional mixing process.In this work,the calcium carbonate whiskers with large length and aspect ratio were prepared.And then the fully biodegradable PLA/CCW composites with highly modulus were prepared through the orientation of whisker in composite.In this paper,the calcium carbonate whiskers with large length and high aspect ratio were prepared by carbonization method using Ca?OH?₂as the raw material and Mg Cl₂?6H₂O as the crystal control agent.The effects of the concentration ratio of magnesium and calcium ions,stirring speed,aeration rate and mode,reaction temperature on the morphology and size of whiskers were investigated.The results showed that the best reaction condition:the reaction temperature was 80?,c _Mg²⁺:c _Ca²⁺=2,the stirring mode was initial stirring speed was 180 rpm,and then the stirring speed was changed to 150 rpm after ventilation for 2 hours,the initial ventilation rate was 3 ml/min,and then changed to 10 ml/min when p H=7.40.Under these conditions,the average length and aspect of whiskers obtained were 98.8?m and 27.9,respctively.Then we prepared the PLA/CCW composite fibers by solution spinning method.And these composite fibers were laminated in some stacking modes and then hot pressed to obtain the PLA/CCW composite with directional aligned whiskers.The experiment results showed that when the content of whisker was no more than 20wt%,many highly oriented whiskers can be observed in composites and the bending properties of composites increased with the addition of whisker.For PLA/CCW?80/20?composite,the orientation degree of whisker in composite was 0.94 and its bending modulus was 7 GPa,which was twice of that of the pure PLA.However,when the content of whisker was more than 20wt%,the bending modulus of composite decreased since the decreasing of the orientation degree of whisker.As the whisker surface was treated by the coupling agent,the non-notched impact strength of the composite can be improved to 21.8 k J/m².In addition,the isotropic PLA/CCW composites can be obtained using appropriate stacking way.