Transcrystallization of polypropylene in the presence of polyester/cellulose nanocrystal composite fibers

Two-step heat fusion kinetics and mechanical performance of thermoplastic interfaces

Thermoplastic polymers and composites are ubiquitous in the industry for their reshaping and fusing capabilities at elevated temperatures. The quality of heat-fused thermoplastic interfaces is of great concern for adhesion, coating, and welding applications, especially those between dissimilar materials. Kinetic evolution of the microstructures defines the mechanical performance of heat-fusion thermoplastic interfaces, which is studied here using polyethylene and polypropylene as an example. Key factors such as the viscosity and compatibility of polymers and the time and temperature of fusion are discussed by combining molecular-level simulations and structural-level hot-compression experiments. Inter-diffusion and entanglement of polymer chains are identified as the two elementary kinetic steps of the fusion, which dominate the control on the stiffness and strength of the interfaces, respectively. Experimental data shows that the quality of fused interfaces can be improved by reducing the viscosity and the interaction parameter. Following the same set of time-scaling relations as identified in the simulations, the two-step characteristics and their effects on the stiffness and strength are experimentally validated. Both simulation and the experiment results show that Young's modulus of fused interfaces recovers faster than the strength that is controlled by polymer entanglement to a large extent, rather than diffusion. These findings add insights into the design of fusion processes, laying the ground for the applications of thermoplastic polymers and composites.

Surface Modification of Staple Carbon Fiber by Dopamine to Reinforce Natural Latex Composite

Carbon fiber significantly enhances the mechanical, thermal and electrical properties of rubber composites, which are widely used in aerospace, military, national defense and other cutting-edge fields. The preparation of a high-performance carbon fiber rubber composite has been a research hotspot, because the surface of carbon fiber is smooth, reactive inert and has a poor adhesion with rubber. In this paper, a high-performance rubber composite is prepared by mixing dopamine-modified staple carbon fiber with natural latex, and the mechanisms of modified carbon fiber-reinforced natural latex composite are explored. The experimental results show that the surface-modified staple carbon fiber forms uniform and widely covered polydopamine coatings, which significantly improve the interface adhesion between the carbon fiber and the rubber matrix. Meanwhile, when the concentration of dopamine is 1.5 g/L and the staple carbon fiber is modified for 6h, the carbon fiber rubber composite shows excellent conductivity, thermal conductivity, and dynamic mechanical properties, and its tensile strength is 10.6% higher than that of the unmodified sample.

Polypropylene crystallization at an alumina interface using single walled carbon nanotubes

Interfaces play an important and often limiting role in the mechanical, thermal, and electrical performance of composite materials. Here we suggest a novel method to improve the interfacial interaction in polypropylene-alumina composites using single-walled carbon nanotubes (SWNTs) to nucleate lamellar crystals at the interface. Macroscopic alumina substrates are used to determine the ideal crystallization parameters and investigate the kinetics of crystal growth. SWNTs are uniformly adsorbed to the interface via Van der Waals interactions and lamellar crystals are grown on the surface using isothermal solution processing techniques. Avrami analysis of crystal surface coverage was used to confirm one-dimensional transcrystalline growth commonly seen with SWNT nucleated crystals. Scanning electron microscopy was used to confirm shish-kebab structures present at the SWNT-polypropylene interface. The determined crystallization parameters were used on colloidal solutions of alumina platelets to successfully create uniformly coated particles with an improved interface. This method shows promise for improving the interphase of semicrystalline polymer-ceramic composites to achieve excellent material properties.

A review on versatile applications of blends and composites of CNC with natural and synthetic polymers with mathematical modeling

Cellulose is world's most abundant, renewable and recyclable polysaccharide on earth. Cellulose is composed of both amorphous and crystalline regions. Cellulose nanocrystals (CNCs) are extracted from crystalline region of cellulose. The most attractive feature of CNC is that it can be used as nanofiller to reinforce several synthetic and natural polymers. In this article, a comprehensive overview of modification of several natural and synthetic polymers using CNCs as reinforcer in respective polymer matrix is given. The immense activities of CNCs are successfully utilized to enhance the mechanical properties and to broaden the field of application of respective polymer. All the technical scientific issues have been discussed highlighting the recent advancement in biomedical and packaging field.

Role of Wood Fibers in Tuning Dynamic Rheology, Non-Isothermal Crystallization, and Microcellular Structure of Polypropylene Foams

Microcellular polypropylene (PP)/wood fiber composite foams were fabricated via batch foaming assisted by supercritical CO₂ (scCO₂). Effects of wood fibers on rheology, crystallization, and foaming behaviors of PP were comprehensively investigated. The obtained results showed that the incorporation of wood fibers increased the complex viscosity and the storage modulus of the PP matrix. Jeziorny's model for non-isothermal crystallization kinetics indicated that wood fibers did not change the crystal growth. However, the crystallization rate of the PP matrix was decreased to a certain extent with increasing wood fiber loadings. The wood fiber exerts a noticeable role in improving the cell density and reducing the cell size, despite decreasing the expansion ratio. Interestingly, a "small-sized cells to large-sized cells" gradient cell structure was found around the wood fibers, implying cell nucleation was induced at the interface between wood fiber and PP matrix. When wood fiber loadings were specifically increased, a desirable microcellular structure was obtained. However, further increasing the wood fiber loadings deteriorated the cell structure. Moreover, the crystallinity of the composite foams initially decreased and then slightly increased with increasing wood fiber loadings, while the crystal size decreased.