High-density polyethylene/halloysite nanocomposites: morphology and rheological behaviour under extensional and shear flow

Effect of Nano-SiO2 on Different Stages of UHMWPE/HDPE Fiber Preparation via Melt Spinning

Ultra-high molecular weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) blend with lower viscosity is more suitable for melt spinning compared to pure UHMWPE; however, the mechanical property of the blend fiber is hard to dramatically improve (the maximum tensile strength of 998.27 MPa). Herein, different content modified-nano-SiO₂ is incorporated to UHMWPE/HDPE blend fiber. After adding 0.5 wt% nano-SiO₂, the tensile strength and initial modulus of UHMWPE/HDPE/nano-SiO₂ fiber are increased to 1211 MPa and 12.81 GPa, respectively, 21.57% and 43.32% higher than that of UHMWPE/HDPE fiber. Meanwhile, the influence of the nano-SiO₂ content on the performance for as-spun filament and fiber are emphatically analyzed. The crystallinity and molecular chain orientation of as-spun filament reduces with the addition of nano-SiO₂. On the contrary, for fiber, the addition of nano-SiO₂ promoted the crystallinity, molecular chain orientation and grain refinement more obvious at a lower content. Furthermore, the possible action mechanism of nano-SiO₂ in the as-spun filament extrusion and fiber hot drawing stage is explained.

Manufacturing and Characterization of Environmentally Friendly Wood Plastic Composites Using Pinecone as a Filler into a Bio-Based High-Density Polyethylene Matrix

The use of wood plastic composites (WPC) is growing very rapidly in recent years, in addition, the use of plastics of renewable origin is increasingly implemented because it allows to reduce the carbon footprint. In this context, this work reports on the development of composites of bio-based high density polyethylene (BioHDPE) with different contents of pinecone (5, 10, and 30 wt.%). The blends were produced by extrusion and injection-molded processes. With the objective of improving the properties of the materials, a compatibilizer has been used, namely polyethylene grafted with maleic anhydride (PE-g-MA 2 phr). The effect of the compatibilizer in the blend with 5 wt.% has been compared with the same blend without compatibilization. Mechanical, thermal, morphological, colorimetric, and wettability properties have been analyzed for each blend. The results showed that the compatibilizer improved the filler–matrix interaction, increasing the ductile mechanical properties in terms of elongation and tensile strength. Regarding thermal properties, the compatibilizer increased thermal stability and improved the behavior of the materials against moisture. In general, the pinecone materials obtained exhibited reddish-brown colors, allowing their use as wood plastic composites with a wide range of properties depending on the filler content in the blend.

Effect of the Elongational Flow on the Morphology and Properties of Polymer Systems: A Brief Review

Polymer-processing operations with dominating elongational flow have a great relevance, especially in several relevant industrial applications. Film blowing, fiber spinning and foaming are some examples in which the polymer melt is subjected to elongational flow during processing. To gain a thorough knowledge of the material-processing behavior, the evaluation of the rheological properties of the polymers experiencing this kind of flow is fundamental. This paper reviews the main achievements regarding the processing-structure-properties relationships of polymer-based materials processed through different operations with dominating elongational flow. In particular, after a brief discussion on the theoretical features associated with the elongational flow and the differences with other flow regimes, the attention is focused on the rheological properties in elongation of the most industrially relevant polymers. Finally, the evolution of the morphology of homogeneous polymers, as well as of multiphase polymer-based systems, such as blends and micro- and nano-composites, subjected to the elongational flow is discussed, highlighting the potential and the unique characteristics of the processing operations based on elongation flow, as compared to their shear-dominated counterparts.

The effect of pyrolysis on the chemical, thermal and rheological properties of pitch

Pitch-based carbon fibers are of considerable interest as high-performance materials. There are reports over the last several decades detailing (i) methods of improving pitch-based carbon fiber performance, and (ii) reducing the cost of production via novel processing techniques. However, there remain considerable challenges in producing high-performance pitch-based carbon fibers consistently on an industrial scale. This is arguably due to the difficulty of scaling the melt-spinning process to compensate for variability in pitch feedstock quality and a lack of understanding of processing-structure-performance relationships. This work focuses on the early stages of heat treatment (pyrolysis) of isotropic pitch and its effect on the chemical, thermal, and rheological properties of the pitch, which help determine its processability. More specifically, we quantify significant changes in chemical structure, M_w, T_g, T_s, and shear and extensional rheology as a function of pyrolysis time at 400 °C. The extensional rheology, in particular, shows that the 'stretchability' of the pitch samples strongly depends on pyrolysis severity, and is important for characterizing 'drawability'. Using a novel analysis of the uniaxial stretching kinematics, we show an isothermal 'drawability window' that allows for the largest axial and radial Hencky strains at constant rate. We hypothesize that this extensional drawability window could facilitate the successful processing of pitch into high quality fiber, minimizing the trial-and-error approach currently used in the field.

Effect of processing condition and antioxidants on visual properties of multilayer post-consumer recycled high density polyethylene films

Mechanical recycling is a promising approach to reduce the environmental impact of plastic packaging waste. However, the presence of defects in recycled materials results in final products with relatively poor visual and/or mechanical properties. In this work, the origin of the visual defects in post-consumer recycled HDPE (PCR HDPE), as well as the effects of processing method, processing condition and the addition of antioxidants on the visual defects were studied in multilayer flexible polyethylene films. The nature of the defects in the film samples were investigated by combining optical microscopy, energy dispersive X-ray (EDX), hot stage microscopy, solvent extraction, and differential scanning calorimetry (DSC) techniques. It was found that the defects in PCR film samples can be mainly categorized as fiber defects and point gels. Hot stage microscopy results show that point gels can be subcategorized in two groups: (a) non-melting, non-deformable gels, and (b) melting, deformable defects. In addition, it was found that deformation of molten, deformable defects increased at higher temperatures specifically above 200 °C. Further characterizations showed that the observed deformable defects are highly entangled high molecular weight HDPE. The effect of processing temperature, processing with a twin-screw extruder and the addition of antioxidant on the visual defects in film samples were also discussed in detail. It was shown that increasing processing temperature and using twin-screw extruders were two approaches that could reduce considerably the number of defects. The addition of antioxidants was also shown to improve the film quality especially at lower processing temperatures.

Upgrading Argan Shell Wastes in Wood Plastic Composites with Biobased Polyethylene Matrix and Different Compatibilizers

The present study reports on the development of wood plastic composites (WPC) based on micronized argan shell (MAS) as a filler and high-density polyethylene obtained from sugarcane (Bio-HDPE), following the principles proposed by the circular economy in which the aim is to achieve zero waste by the introduction of residues of argan as a filler. The blends were prepared by extrusion and injection molding processes. In order to improve compatibility between the argan particles and the green polyolefin, different compatibilizers and additional filler were used, namely polyethylene grafted maleic anhydride (PE-g-MA 3 wt.-%), maleinized linseed oil (MLO 7.5 phr), halloysite nanotubes (HNTs 7.5 phr), and a combination of MLO and HNTs (3.75 phr each). The mechanical, morphological, thermal, thermomechanical, colorimetric, and wettability properties of each blend were analyzed. The results show that MAS acts as a reinforcing filler, increasing the stiffness of the Bio-HDPE, and that HNTs further increases this reinforcing effect. MLO and PE-g-MA, altogether with HNTs, improve the compatibility between MAS and Bio-HDPE, particularly due to bonds formed between oxygen-based groups present in each compound. Thermal stability was also improved provided by the addition of MAS and HNTs. All in all, reddish-like brown wood plastic composites with improved stiffness, good thermal stability, enhanced compatibility, and good wettability properties were obtained.

Comparing Multi-Walled Carbon Nanotubes and Halloysite Nanotubes as Reinforcements in EVA Nanocomposites

The influence of carbon multi-walled nanotubes (MWCNTs) and halloysite nanotubes (HNTs) on the physical, thermal, mechanical, and electrical properties of EVA (ethylene vinyl acetate) copolymer was investigated. EVA-based nanocomposites containing MWCNTs or HNTs, as well as hybrid nanocomposites containing both nanofillers were prepared by melt blending. Scanning electron microcopy (SEM) images revealed the presence of good dispersion of both kinds of nanotubes throughout the EVA matrix. The incorporation of nanotubes into the EVA copolymer matrix did not significantly affect the crystallization behavior of the polymer. The tensile strength of EVA-based nanocomposites increased along with the increasing CNTs (carbon nanotubes) content (increased up to approximately 40% at the loading of 8 wt.%). In turn, HNTs increased to a great extent the strain at break. Mechanical cyclic tensile tests demonstrated that nanocomposites with hybrid reinforcement exhibit interesting strengthening behavior. The synergistic effect of hybrid nanofillers on the modulus at 100% and 200% elongation was visible. Moreover, along with the increase of MWCNTs content in EVA/CNTs nanocomposites, an enhancement in electrical conductivity was observed.

Polyethylene-Matrix Composites with Halloysite Nanotubes with Enhanced Physical/Thermal Properties

The aim of the present work is to investigate the effect of halloysite nanotubes (HNT) on the mechanical properties of low-density polyethylene composites modified by maleic anhydride-grafted PE (PE-graft-MA). Polyethylene nanocomposites were prepared using an injection molding machine, Arburg Allrounder 320 C 500–170; the HNT content was varied at 0 wt %, 2 wt %, 4 wt % and 6 wt %, and the PE-graft-MA content was varied at 5 wt %. The composites were examined for their ultimate tensile stress, strain at ultimate stress, hardness, impact strength, melt flow rate, heat deflection temperature, Vicat softening temperature, crystallinity degree and phase transition temperature. It was found that the addition of halloysite nanotubes to low-density polyethylene (LDPE) led to an increased heat deflection temperature (HDT, up to 47 °C) and ultimate tensile strength (up to 16.00 MPa) while the Vicat softening temperature, strain at ultimate stress, impact strength and hardness of examined specimens slightly decreased. Processing properties of the materials specified by the melt flow rate (MFR) deteriorated almost twice. The results have demonstrated that the nanoparticles can reinforce enhance LDPE at low filler content without any considerable loss of its ductility, but only when halloysite nanotubes are superbly distributed in the polyethylene matrix.

High-density polyethylene/needle-like sepiolite clay nanocomposites: effect of functionalized polymers on the dispersion of nanofiller, melt extensional and mechanical properties

Influence of molar mass and polarity of PE-g-MA on different properties [Morphological, Melt extensional, Mechanical and Thermal] of HDPE/sepiolite nanocomposites is reported.