Preparation And Research On The Interfacial Properties Of Polyethylene Or Polypropylene Based Microcrystalline Cellulose Composites

Over the last decades,due to the increasing ecological conditions,the natural fibres,which are potentially suitable for reinforcing thermoplastics,are currently being emerged as desirable reinforcements within polymeric matrices in preparation of bio-composites for several engineering applications.The dominating problems encountered during the extrusion and injection molding processes are poor interfacial adhesion between the natural fillers and polyolefin matrix,thus,we adopted a series of physical and chemical means to improve the interfacial compatibility of their composites.(1)The microcrystalline cellulose fibres were mercerized by NaOH aqueous sulution at 2?,avoiding the occurrence of thermal degradation.The iPP/MCC-II composites were melt blending by slurry method,which effectively prevented the agglomeration phenomenon of MCC-II fibers.MCC-II can induce iPP to form a hybrid shish-calabash crystalline structure(HSC)observed by hot stage polarized optical microscopy(POM),and the non-isothermal crystallization behavior is consistent with the Avrami equation.(2)The refined iPP particles were obtained by mechanical pulverization,cryogenic grinding and high-pressure homogenizing emulsification,respectively.The crystalline structure of iPP was partially destroyed,and some ? crystals were transformed into ? crystals,which resulted in a reduction in stability of iPP and the iPP/MCC composites.The crystallinity of MCC increased first and then decreased during the high pressure homogenizing process,and its redispersibility in water was improved after directly drying.The addition of MCC fibrers can improve the mechanical properties of iPP/MCC composites to a certain extent,meanwhile,refined iPP can effectively be used as a physical barrier agent to avoid the occurrence of agglomeration of MCC in their composites.(3)MCC boned with coupling agent can induce iPP to form more dense nuclei on its fiber chain observed by the POM.And the polar end groups of coupling agent seriously affected the nucleation efficiency of MCC molecular chain.The ability of coupling agent bonded MCC to induce iPP crystallization has decreased,however,the initial degradation temperature(T05)of their composites has increased.The thermal stability of the iPP/MCC composites increased with the addation of coupling agent KH550,and the mechanical properties achieved the optimal values when adding 1.5wt% of KH550.(4)The efficient compatibilizer for iPP/MCC composites was obtained by melt extruding of iPP: diethyl maleate(DEM):diisopropyl peroxide(DCP)=100: 0.3: 3 at the rotation of 60r/min,and the grafting degree and the melt flow rate(MFR)reached 2.16% and 45.8g/(10min),respectively.FTIR confirmed this grafting process by the appearance of C=O absorption peak.The comonomer styrene(St)with electron-donating properties solved the degradation problem in the free radical graft polymerization of iPP,and improved the grafting degree at the same time.The contact angle of the pure grafted polymer surface had been reduced.The introduction of grafting monomer disrupted the regular arrangement of iPP molecules,resulting in a decrease in the crystallinity and thermal stability of iPP.On the other hand,the introduction of compatibilizer PP-g-DEM and PP-g-(DEM-St)improved the interface compatibility between iPP and MCC and consequently improved the mechanical properties of their composites.(5)Self–made calcium pimelate can be used as an effective beta nucleating agent for iPP to accelerate its crystallization process,especially to improve the elongation at break,notched impact strength and also transparency of iPP/MCC/Cast composites.The results shown a decrease in thermal stability of composites due to the presence of thermally metastable beta form iPP.(6)The thermal stability of LDPE/NCC composite membrane was seriously affected by the dispersion uniformity of NCC in the LDPE matrix.The introduction of PEG could effectively prevent the occurrence of NCC agglomeration and control the pore size and distribution by changing the adding amount.Moreover,the introduction of cellulose fibres provided a continuous transportation waypath for the permeable composite membranes,which improved their permeability.