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Natural cellulose is a kind of environmentally friendly materials widely used in pharmaceutical and plastic processing industry for its excellent biodegradability and mechanical performance. The aim of this paper was to prepare hybrid nanocellulose film with cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) and evaluate the morphological structure, mechanical performance, thermal stability, and light transmittance of the film obtained by vacuum suction filtration method. Acid hydrolysis and high pressure homogenization methods were used to produce CNC and CNF with the help of different acid, alkali, and salt solution. The results revealed that the content of CNF was closely related to the tensile property while the CNC was beneficial to the light transmittance. A rough surface and bumps could be observed in nanocellulose film containing CNC or CNF only. A combination of rod like CNC and filamentous CNF could bring about a balance between mechanical performance, thermal stability, and light transmittance. The results obtained in this paper can offer significant reference to the formula design and optimization of processing parameters in manufacturing of nanocellulose film for packaging in mass production with excellent comprehensive performance.

Polypropylene melt-blown fabric as the core filter materials plays an important role in manufacturing civil and medical epidemic prevention products. The aim of this study was to optimize and control the particle filtration efficiency and apparent surface quality of the melt-blown fabric from the perspectives of electret masterbatch composition and processing parameters. Magnesium stearate and fumed silica were used as the electret to manufacture polypropylene melt-blown fabric. The layout and charge voltage of the electret device was taken as the variables to optimize and improve the particle filtration efficiency and bulkiness coefficient of the fabric. The temperature of the barrel and die was controlled to enhance the surface quality and corresponding particle filtration efficiency. The results showed that a combination of organic magnesium stearate and inorganic fumed silica could obtain a balance between particle filtration efficiency and smooth processing without being jammed. Increasing the charge voltage and rearranging the position of the charge wires could significantly enhance the particle filtration efficiency. A better particle filtration efficiency and reasonable bulkiness coefficient could be obtained by controlling the diameter of the filaments by regulating the temperature of the barrel and die as well as the suction intensity. The results obtained from this study can offer valuable references in optimization of electret master batch formulation and processing parameters for melt-blown fabric production with different resin.

Demand for natural fibers reinforced composites is growing as an alternative to synthetic fiber reinforced plastic composites. However, poor compatibility between natural fiber and matrix has limited its development. Therefore, it is necessary to improve their interfacial adhesion to improve the comprehensive properties of composites. In this work, sisal fibers were subjected to an alkali/polyvinyl alcohol coating treatment by an ultrasonic impregnation method, and the sisal/high-density polyethylene composite was prepared by a twin-screw extruder. The Fourier transform infrared spectroscopy was used to characterize the modification effect of sisal fiber. The surface morphology of sisal fiber and the interfacial morphology of sisal/high-density polyethylene composites were observed. The mechanical properties and water absorption of sisal/ high-density polyethylene composites were also studied. The results show that alkali/polyvinyl alcohol coating compound treatment can effectively improve the interfacial adhesion between sisal fiber and high-density polyethylene, improve the mechanical properties of composite, and reduce water absorption. Alkali/polyvinyl alcohol coating compound treatment is a very environment-friendly, cost-effective fiber modification method when compared with traditional modification methods. It is helpful for the development and application of natural fibers reinforced composites.

Relaxation behavior of natural fiber reinforced polymer composites exists in both solid and molten state and profoundly affects the control and optimization of processing parameters and dimensional accuracy of final products. The aim of this study was to establish an experimental estimating method to characterize relaxation behavior of polymer composite with traditional torque rheometer and investigate the effects of fiber concentration, dimension, and processing parameters on the relaxation behavior. Relaxation time of hemp fiber reinforced polypropylene composite were obtained by fitting the experimental torque data and corelated to the buckling deformation of packaging boxes manufactured by injection with the same injection parameters. The results show that all the increasing concentration of hemp fiber, higher rotor speed, and higher temperature can significantly decrease the relaxation time and result in a stable and better dimensional accuracy of injection packaging boxes. The finer fibers with the same weight concertation can bring an obvious reduction in relaxation time and buckling deformation. The proposed method for estimating relaxation behavior of polymer composite is a feasible and cost-effective way to investigate the viscoelastic properties of polymer composites close to the real processing conditions. And it can be widely used in optimization of processing parameters and performance of polymer composite products.

Structures, working mechanism, data collecting and processing methods of the self-made multifunctional all-electronic rheometer for polymer composites were introduced in detail. The validity of this equipment was proved by deriving the apparent shear viscosity expression under axial vibration condition and comparing the results obtained from both this self-made rheometer and Rosand Rh7D capillary rheometer at steady state. With this equipment, the effects of calcium carbonate weight fraction, particle size and vibration parameters on apparent shear viscosity of calcium carbonate filled propylene composites were investigated. The results show that: the apparent shear viscosity of the composites increases with the filled particle concentration. However, it is seldom affected by particle size within certain a range of shear rate. While the apparent shear viscosity increases with the decrease of particle size at moderate shear rate. Besides, the apparent shear viscosity declines rapidly with the increasing vibration amplitude. However it exhibits a cosinoidal or sinusoidal trend as vibration frequency increases and peaks at the resonant frequency of the composites.