Research On The Preparation And Performance Of Poly (Lacticacid)/coated Calcium Carbonate Composites

As the application of polymer materials in biomedicine,packaging,agriculture and other fields continues to expand,the pollution problems caused by them are also becoming more and more serious.Polylactic acid?PLA?is a biodegradable polymer material with high performance,that is expected to play an important role in solving white pollution problems.The PLA/coated calcium carbonate composites proposed in this paper can reduce the cost of PLA products,promote the natural degradation of composite materials,improve the utilization value of PLA and expand the scope of application.In this paper,We choose starch as the main modifier,sodium stearate,sodium hexametaphosphate as secondary modifiers,coated with calcium carbonate.Finally,we prepared starch coated calcium carbonate.By single factor experiments and orthogonal test optimization,we get the best modification conditions:The mass ratio of starch to calcium carbonate is 1:5,the amount of sodium hexametaphosphate added is 10%of the mass of starch,and the cross-linking reaction temperature is 50?.The coated calcium carbonate was analyzed by means of Fourier transform infrared spectroscopy?FT-IR?,laser particle size analyzer,Zeta potentiometer and scanning electron microscope?SEM?.We found:the coated calcium carbonate had a obvious glucose ring infrared absorption peak at 1024cm^-1,the median diameter D?0.5?increased from 6.265?m to 9.183?m and the Zeta potential changed from+2.63mv to-8.12mv.Analysis showed that the surface of calcium carbonate was successfully coated with a layer of starch film.SEM found:compared with unmodified calcium carbonate's sharp edges,the coated calcium carbonate have blunt edges,the particles are rounded.We prepared PLA/coated calcium carbonate,PLA/calcium carbonate composites by melt blending method,under the action of plasticizer glycerol.Through the study of interfacial properties,tensile properties and thermal stability of the composites,it was found that under the action of plasticizer glycerol,PLA/coated calcium carbonate composites have a better interfacial compatibility,reduce the interface stress concentration,therefore,the tensile properties of composites are improved.Taking 15wt%of the composite material as an example,the tensile strength and elongation at break of the polylactic acid/15wt%calcium carbonate composite are 43.0 MPa and 3.75%,respectively,the polylactic acid/15wt%coated calcium carbonate composite are 46.1Mpa and 4.04%,increased by 7.2%and 7.7%respectively.Compared with pure PLA,the melting temperature decreased about 5-7?,decomposition temperature decreased about 50-60?.The degradation of PLA/coated calcium carbonate composites was studied by soil-buried degradation test.It was found that the addition of coated calcium carbonate promoted the degradation rate of the composites.During the whole process of degradation,the starch part of the composite degrade firstly,and the pores are formed on the surface and inside of the material,which is favorable for the adhesion between mold and water on the surface of the material and the erosion of the material inside,promotes the overflow of the coated calcium carbonate,Promote the hydrolysis and biodegradation of PLA matrix.The overall rate of degradation of composite materials accelerated,On the one hand,the interfacial clearance between the coated calcium carbonate and the PLA matrix contributes to the erosion of the material by water molecules or molds,on the other hand,the starch part of the coated calcium carbonate is a kind of hydrophilic polysaccharide material,which has a faster rate of hydrolysis and biodegradation by itself,provides nutrients for the molds,make a great contribution on the overall degradation rate of composite material.