Investigation on the uniformity of high-density polyethylene/wood fiber composites in a twin-screw extruder

Mechanical Properties Variation in Wood-Plastic Composites with a Mixed Wood Fiber Size

In this study, the influence of fiber particle size on the mechanical properties of a wood--plastic composite (WPC) was investigated using a combination of experimental measurements and numerical modeling. Four different sizes of wood fibers (10-20 mesh, 20-40 mesh, 40-80 mesh, and 80-120 mesh) were used to reinforce high-density polyethylene (HDPE), either separately or in combination. The different sizes of fibers produced varying properties in the resulting composites. The smallest fiber size (80-120 mesh) resulted in the lowest flexural and tensile properties, but the highest impact strength (15.79 kJ/m2) compared to the other three sizes (12.18-14.29 kJ/m2). Using a blend of fiber sizes resulted in improved mechanical properties. Composites containing a mix of 20-40 mesh and 40-80 mesh fibers exhibited the best flexural (strength 74.16 MPa, modulus 5.35 GPa) and tensile performance (strength 48.27 MPa, modulus 4.30 GPa), while composites containing a mix of all four fiber sizes had the highest impact-resistant strength (16.08 kJ/m2). Several models, including the Rule of Mixtures (ROM), the Inverse Rule of Mixtures (IROM), and the Hirsch models, were used to predict the performance of WPCs. The ROM model was found to be the most accurate in describing the mechanical properties of WPCs reinforced with multi-size wood fibers, based on the sum squared error (SSE) analysis.

Potential use of waste from tree pruning and recovered plastic to obtain a building material: Case study of Merida, Mexico

This work presents a study on the use of wood and plastic wastes generated in abundance in Merida, Mexico, to help to reduce them in order to mitigate environmental deterioration. The use of these wastes is proposed to obtain a low-cost building material. So, the escalation process (i.e., extrusion) at the pilot level to obtain a prototype of a wood-plastic composite (WPC) corrugated sheet to evaluate the technical feasibility to make a low-cost product is reported. A corrugated sheet with recycled high-density polyethylene (R-HDPE) was produced. The R-HDPE was collected from Merida's Separation Plant. The wood came from the trimmings of different varieties of trees and shrubs that are periodically pruned. WPC sheets with virgin HDPE were prepared to assess its effect on the materials' mechanical performance. The wood/HDPE weight ratio was 40/60. The performance of the WPC sheets was compared with that of commercial products with similar characteristics, namely acrylic and polyester sheets reinforced with fibreglass, and black asphalt-saturated cardboard sheets. Thus, the effect of natural weathering on the maximum tensile tearing force and on the maximum flexural load of the different types of sheets was evaluated. Although the mechanical performance of the WPC sheets was lower than that of the acrylic and polyacrylic sheets, their performance was much better than that of the cheap black asphalt-saturated cardboard sheets. So, they are a good option to be used as low-cost temporary roofing.

A Review of Wood Polymer Composites Rheology and Its Implications for Processing

Despite the fact that wood polymer composites are interesting materials for many different reasons, they are quite difficult to shape through standard polymer processing techniques, such as extrusion or injection molding. Rheological characterization can be very helpful for understanding the role played by the many variables that are involved in manufacturing and to achieve a good quality final product through an optimized mix of formulation and processing parameters. The main methods that have been used for the rheological characterization of these materials are capillary and parallel plate rheometry. Both are very useful: rotational rheometry is particularly convenient to investigate the compounding phase and obtain structural information on the material, while capillary viscometry is well suited to understand final manufacturing. The results available in the literature at the moment are indeed very interesting and are mostly aimed at investigating the influence of the material formulation, the additives in particular, on the structural, mechanical, and morphological properties of the composite: despite a good number of papers, though, it is difficult to draw general conclusions, as many issues are still debated. The purpose of this article was to overview the state of the art and to highlight the issues that deserve further investigation.

Application of Raman Spectroscopy for In-Line Measurement of Dispersion Uniformity of Polypropylene-Polystyrene Blends During Melt Extrusion

At present, there is a widespread phenomenon that product quality is difficult to monitor during the process of polymer melt modification such as blending, filling, and reinforcement. In consideration of this problem, this paper proposes an in-line Raman spectroscopy technique for measuring dispersion uniformity of polystyrene (PS) in polypropylene (PP)/PS blends during melt extrusion. On the basis of the optimal partial least squares (PLS) calibration model for quantitative determination of PS content in PP/PS, the fluctuations of PS content in extruding PP/PS with a mass percentage of 70 : 30 at different screw rotation speeds were predicted. The coefficient of variation (CV) of PS content at each screw rotation speed was obtained to accurately compare the dispersion uniformity, which was in agreement with the PS dispersion result characterized by the scanning electron microscope (SEM). In addition, the sensitivity of the measurement was validated by calculating the CV of PP/PS with mass percentages of 69 : 31 and 71 : 29. All of the above demonstrated that the in-line measurement system of Raman spectroscopy was able to accurately measure the dispersion uniformity of PS during the blending extrusion of PP/PS and demonstrated good sensitivity to minor changes in the blends composition.

Foam extrusion of PP-based wood plastic composites with chemical blowing agents and the Celuka technique

Wood plastic composites have gained relevance in recent years as an alternative to wood boards. However, because the cavities in wood fibres are compressed by high processing pressure during the extrusion of wood plastic composites, the product densities show a range of up to 1.5 g/cm3 depending on wood content and base material. Particularly in large-sized products, this may be disadvantageous for processors and end users. Foaming of the plastic matrix is a promising approach to reduce the density of wood plastic composites products. This article discusses the foam extrusion of PP-based wood plastic composites with chemical blowing agents in combination with the Celuka technique. Integral wood plastic composites foam with a rigid and plain outer layer was produced using a parallel, counter rotating twin screw extruder. The profiles obtained were analysed with respect to foam structure and mechanical properties. It was possible to achieve a density reduction of up to 0.7 g/cm3 in the foamed wood plastic composites profiles. Furthermore, we demonstrate that wood fibre length and type of chemical blowing agent have a strong effect on the resulting foam morphology.