Optimization of Thermal and Mechanical Properties of Polypropylene-Wollastonite Composite Drawn Fibers Based on Surface Response Analysis

The thermal and mechanical properties of polypropylene-wollastonite composite drawn fibers were optimized via experiments selected with the Box-Behnken approach. The drawing ratio, the filler and the compatibilizer content were chosen as design variables, while the tensile strength, the melting enthalpy and the onset decomposition temperature were set as response variables. Drawn fibers with tensile strength up to 535 MPa were obtained. Results revealed that the drawing ratio is the most important factor for the enhancement of tensile strength, followed by the filler content. All the design variables slightly affected the melting temperature and the crystallinity of the matrix. Also, it was found that the addition of polypropylene grafted with maleic anhydride as compatibilizer has a multiple effect on the final properties, i.e., it induces the dispersion of both the antioxidant and the filler, tending to increase thermal stability and tensile strength, while, on the same time, deteriorates mechanical and thermal properties due to its lower molecular weight and thermal stability. Such behavior does not allow for simultaneous maximization of thermal stability and tensile strength. Optimization based on a compromise, i.e., targeting maximization of tensile strength and onset decomposition temperature higher than 300 °C, yields high desirability values and predictions in excellent agreement with verification experiments.

Experimental Investigation of Polypropylene Composite Drawn Fibers with Talc, Wollastonite, Attapulgite and Single-Wall Carbon Nanotubes

Isotactic polypropylene (PP) composite drawn fibers were prepared using melt extrusion and high-temperature solid-state drawing at a draw ratio of 7. Five different fillers were used as reinforcement agents (microtalc, ultrafine talc, wollastonite, attapulgite and single-wall carbon nanotubes). In all the prepared samples, antioxidant was added, while all samples were prepared with and without using PP grafted with maleic anhydride as compatibilizer. Material characterization was performed by tensile tests, differential scanning calorimetry, thermogravimetric analysis and Fourier transform infrared spectroscopy. Attapulgite composite fibers exhibited poor results in terms of tensile strength and thermal stability. The use of ultrafine talc particles yields better results, in terms of thermal stability and tensile strength, compared to microtalc. Better results were observed using needle-like fillers, such as wollastonite and single-wall carbon nanotubes, since, as was previously observed, high aspect ratio particles tend to align during the drawing process and, thus, contribute to a more symmetrical distribution of stresses. Competitive and synergistic effects were recognized to occur among the additives and fillers, such as the antioxidant effect being enhanced by the addition of the compatibilizer, while the antioxidant itself acts as a compatibilizing agent.

Fabrication of reinforced and toughened PC/PMMA composites by tuning the migration and selective location of graphenes during melt blending

In this work, we creatively obtained reinforced and toughened PC/PMMA/GNs composites by tuning the migration and selective location of graphene nanosheets (GNs) during melt blending. TEM results revealed that the migration of GNs in PC/PMMA blends during melt blending always existed no matter how the GNs were introduced, and most of them exclusively localized at the interface of PC and PMMA phase due to interfacial effects. The migration of GNs could refine the size of the dispersed phase, and the exclusive localization of GNs at the interface show obvious interfacial compatibilizing effects, leading to improved mechanical properties of the composites. It was found that the composite prepared by one-step compounding showed significant enhanced strength and toughness with addition of mere 0.05 wt% GNs and the tensile strength and elongation of the composite increased by about 62.96% and 94.54%, respectively as compared to the PC/PMMA blends. Moreover, the composite prepared by one-step compounding also showed improved thermal conductivity at the same time, indicating excellent comprehensive properties. It is believed that tuning the migration and selective localization of GNs open perspectives for the development of high-performance polymer composites.

By adjusting the dispersion and distribution of graphene nanosheets (GNs) filler in polycarbonate/polymethyl methacrylate (PC/PMMA) composites, only 0.05 wt% GNs filler can significantly improve the strength and toughness of the composites.

Preparation and properties of long chain branched high-density polyethylene based on nano-SiO2 grafted glycidyl methacrylate

A compounded nanoparticle with multiple double bonds (C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C) was prepared by grafting glycidyl methacrylate (GMA) onto the surface of nano-SiO₂. Then gel-free long chain branched polyethylene (LCBPE) was prepared by melt branching reaction in a Haake torque rheometer in the presence of initiator peroxide and GMA grafted nano-SiO₂ (SiO₂-g-GMA). The sampling time corresponded to the summit of the reaction peak in the torque curve. Fourier transform infrared results indicated that SiO₂-g-GMA had been grafted onto the HDPE backbone via radical reaction. The reaction mechanism and the topological structure of the PE products are also discussed. Rheological results showed that the relaxation time and molecular weight distribution of modified PE were increased owing to the introduction of LCB structure, and the more SiO₂-g-GMA was added, the more apparent variation could be observed. Compared with linear HDPE, both the melt strength and mechanical properties of LCBPE were improved obviously. From the differential scanning calorimetry and polarized optical microscopy results, smaller crystal size and lower growth rate were observed compared with linear HDPE, which are ascribed to the nucleation and restriction of long branching chains in the system. Well distributed nano-SiO₂ without any agglomeration in the PE matrix was observed in the scanning electron microscope images when the SiO₂-g-GMA content was less than 3 phr.

A compounded nanoparticle with multiple double bonds (CC) was prepared by grafting glycidyl methacrylate (GMA) onto the surface of nano-SiO₂.

Understanding the mechanical and thermal property reinforcement of crosslinked polyethylene by nanodiamonds and carbon nanotubes

A systematic evaluation of the factors governing the measured thermal and mechanical property reinforcement in crosslinked polyethylene nanocomposites is presented.