Preparation And Properties Of The Microcellular Foamed Microcrystalline Cellulose/Polylactide Composites

As a biocompatible and environmentally-friendly fully biodegradable material,Polylactide(PLA)has excellent mechanical properties compared with petroleum based plastics,but the brittleness limits its wide application in many fields.By supercritical carbon dioxide(ScC02)microcellular foaming technology,the introduce of microporous structure in PLA interior can improve the PLA toughness meanwhile reduce the cost.However,PLA belongs to semi-crystalline polymer,slow crystallization rate,poor heat resistance,the low melt strength,easy to appear bubble phenomenon in the foaming process such as hole collapse,rupture,merge,which resulted in the difficulty in foam molding and the poor foaming performance.The addition of Microcrystalline cellulose(MCC)can improve the heat resistance and to enhance foaming materials,increasing the foaming density of PLA finally obtaining a fully degradable composite material.However,MCC is easily agglomerated by intermolecular hydrogen bonding,which is not conducive to the preparation of MCC/PLA microcellular foamed composites with good cell structure.This research adopts the "high temperature and pressure maintaining,low temperature foaming" two-step foaming process,and using clean,cheap and efficient supercritical CO2 as foaming agent,to prepare the MCC/PLA microcellular foamed composites.This investigation identified the optimum adding amount of MCC which can effectively promote the cell heterogeneous nucleation,the esterification to MCC and addition of compatibilizer were respectively used to improve MCC dispersed in the PLA.exploring the effects of different methods on the crystallization,the rheological behavior MCC/PLA composite system,and the influence on cell structure and the foamed performance of the foamed material.The main research results are as follows:The preparation and properties of MCC/PLA microcellular foamed composites were studied.The addition of MCC reduced the complex viscosity and energy storage modulus of PLA melt,improved the crystallinity of PLA,and had a great impact on the foamed performance of PLA/MCC composites.Compared with pure PLA,the foamed ratio increased obviously and the apparent density decreased.When the content of MCC is 3 wt%,the cell density increases to 9.3×108 cell/cm3,the cell size decreases,the average cell diameter is 37.24 ?m,when near the MCC,the cell size gradient distribution,but the foamed material porosity rate is high,continue to adding MCC,the cell structure deterioration.Through the esterification on the surface of MCC by using aromatic carboxylic acid,the crystallinity and thermal stability of modified MCC(g-MCC)were improved,the polarity was weakened,the dispersion was better improved in the non-polar PLA matrix,forming the filler network structure.The crystalline properties and rheological properties of the composites were improved,and the melt viscoelasticity was increased,the foamed properties were improved.After modification,the 5 wt%content of MCC in the composite system showed uniform distribution of cell size,the average cell diameter decreased from 42.36 ?m to 34.01 ?m,the cell density increased from 8.3× 108 cell/cm3 to 1.1 × 1010 cell/cm3,and the cell structure was significantly improved.Using Styrene-assisted free-radical melt grafting of MAH onto PLA(PLA-g-St/MAH)as compatibilizer significantly improved the interfacial compatibility of the MCC/PLA composite and the foamed performance.The compatibilizer reduced the interfacial gap between MCC and PLA,improved the melt strength of the composite system,enhanced the melting temperature and crystallinity.Compatilizer could improve the foamed properties of MCC/PLA composite system,the cell density of foamed material grown,cell size decreased,obturator rate increased.When the compatibilizer content is 3 wt%,average cell size of 30.58 ?m,cell density improve an order of magnitude,the cell shape rules,bubble pore structure ideal microcellular foaming composite materials.