Preparation Of CNF/Polymer Composites By Pickering Emulsion Gel Method And Research On Their Properties

With the emergency of nanoscience and technology,nanocellulose plays an unpredictable application value in the reinforced composites field due to its high aspect ratio,high mechanical strength and good biocompatibility.The research on cellulose nanofiber(CNF)stabilized Pickering emulsion by which the related functional materials were prepared has aroused great interests in the materials science field.In this paper,CNF,which was prepared from sisal fiber,was used as solid stabilizer for Pickering emulsion.For the preparation of the emulsion gel,a certain concentration of CNF dispersion as water phase was mixed with a certain concentration of 1,2-dichloroethane(DCE)solution including hydrophobic polymer as oil phase according to a certain volume ratio of water to oil following ultrasonic emulsification.Further,hot pressing process was used to obtain the CNF reinforced polymer composite films with excellent mechanical properties and high optical transparency.The morphology structure and formation mechanism of composite films were studied.The details are as follows:(1)By using CNF stabilized Pickering emulsion gel technology and hydrophobic polymer as matrix,CNF/polymer composite films were prepared simply and rapidly by vacuum filtration,solvent washing and hot pressing method.The morphology,structure and properties of the composite films were studied.The results show that the obtained CNF/polymer composite films had three-dimensional network reinforcement structure of unique multi-scale,which were formed by CNF three-dimensional network with nanoscale and CNF/polymer composite layer three-dimensional network with microscale,respectively.(2)The formation mechanism of three-dimensional network structure with multi-scale of CNF/polymer composite films were discussed.The results shown that in the two-step hot pressing process,under the low temperature and low pressure a small amount of residual solvents can induce the polymer to exude from the emulsion droplets into the three-dimensional network structure of the nanoscale CNF.Under the subsequent high temperature and high pressure,the molten polymer was further exuded into the three-dimensional network structure of CNF to form CNF/polymer composites.Those polymer reserved in droplets embedded in a microscale three-dimensional network structure of CNF/polymer composites.Finally,a multi-scale three-dimensional network structure of C-CNF/polymer composite films were formed.(3)CNF/PMMA and CNF/PS composite films were prepared separately by introducing PMMA or PS into the oil phase,and their properties were studied.CNF/PMMA composite film had very low linear thermal expansion coefficient.Compared with pure PMMA and PS films,the tensile strength of CNF/PMMA and CNF/PS composite films increased by 400%and 360%respectively,while maintaining high transmittance of 87%and 84%,respectively.T_g decreased first and then increased resulted from the special multi-scale three-dimensional network structure of the composite films.(4)CNF/PMMA/PS ternary composite materials were prepared by introducing PMMA and PS into the oil phase simultaneously.The effects of coexistence of different polymers on structure and morphology of the Pickering emulsion gel and the final composite material was studied.The results shown that when PMMA and PS coexisted in oil phase simultaneously,the particle size of emulsion droplets decreased obviously,and polymer blends were difficult to penetrate into network structure of CNF.The structure of CNF/polymer composite layer was discontinuous,which led to the reduction of transparency of the composite films compared with binary composite films,but it still kept the transmittance of 80%.Compared with PMMA/PS blend films,the compatibility between PMMA and PS in the composite films was improved significantly,while its mechanical property went up by 600%.