摘要
The evolution and the origin of“solid-like state”in molten polymer/clay nanocomposites are studied.Usingpolypropylene/clay hybrid(PPCH)with sufficient maleic anhydride modified PP(PP-MA)as compatibilizer,well exfoliationyet solid-like state was achieved after annealing in molten state.Comprehensive linear viscoelasticity and non-lineartheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on time,temperature and deformation dependencies of the“solid-like”state in molten nanocomposites.Based on these,it is revealedthat the solid-structure is developed gradually along with annealing through the stages of inter-layer expansion by PP-MA,the diffusion and association of exfoliated silicate platelets,the formation of band/chain structure and,finally,a percolatedclay associated network,which is responsible for the melt rigidity or solid-like state.The network will be broken down bymelt frozen/crystallization and weakened at large shear or strong flow and,even more surprisingly,may be disrupted by usingtrace amount of silane coupling agent which may block the edge interaction of platelets.The solid-like structure causescharacteristic non-linear rheological behaviors,e.g.residual stress after step shear,abnormal huge stress overshoots in stepflows and,most remarkably,the negative first normal stress functions in steady shear or step flows.The rheological andstructural arguments challenge the existing models of strengthened entangled polymer network by tethered polymer chainsconnecting clay particles or by chains in confined melts or frictional interaction among tactoids.A scheme of percolatednetworking of associated clay platelets,which may in band form of edge connecting exfoliated platelets,is suggested toexplain previous experimental results.
The evolution and the origin of“solid-like state”in molten polymer/clay nanocomposites are studied.Usingpolypropylene/clay hybrid(PPCH)with sufficient maleic anhydride modified PP(PP-MA)as compatibilizer,well exfoliationyet solid-like state was achieved after annealing in molten state.Comprehensive linear viscoelasticity and non-lineartheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on time,temperature and deformation dependencies of the“solid-like”state in molten nanocomposites.Based on these,it is revealedthat the solid-structure is developed gradually along with annealing through the stages of inter-layer expansion by PP-MA,the diffusion and association of exfoliated silicate platelets,the formation of band/chain structure and,finally,a percolatedclay associated network,which is responsible for the melt rigidity or solid-like state.The network will be broken down bymelt frozen/crystallization and weakened at large shear or strong flow and,even more surprisingly,may be disrupted by usingtrace amount of silane coupling agent which may block the edge interaction of platelets.The solid-like structure causescharacteristic non-linear rheological behaviors,e.g.residual stress after step shear,abnormal huge stress overshoots in stepflows and,most remarkably,the negative first normal stress functions in steady shear or step flows.The rheological andstructural arguments challenge the existing models of strengthened entangled polymer network by tethered polymer chainsconnecting clay particles or by chains in confined melts or frictional interaction among tactoids.A scheme of percolatednetworking of associated clay platelets,which may in band form of edge connecting exfoliated platelets,is suggested toexplain previous experimental results.
基金
This work was funded by the NSFC of China(No.20490220)
Major State Basic Research Projects(2003CB615604)
SINOPEC Petrochemical Co.Ltd.(Project X501029).
