Ghaus M. Rizvi

Effects of Lubricant Content on Extrusion Processing and Mechanical Properties of Wood Flour-High-density Polyethylene Composites:

Wood plastic composite (WPC) development has been facilitated by the economical extrusion of WPC profiles for various applications. The physical and mechanical properties of WPC products can be optimized by regulating extrusion processing conditions and material formulations. Rectangular WPC profiles were produced with varied high-density polyethylene (HDPE), wood fiber (WF), and lubricant contents under different extrusion conditions in a twin-screw extruder extrusion line. Optimal tensile and flexural properties were obtained with 50 wt% WF at 7 and 3 wt% lubricant and maleated polyethylene (MAPE) contents. The apparent shear viscosity of the WPC melts decreased gradually with increased lubricant content. Hence, for practical applications, a combination of HDPE grade, WF, lubricant, and MAPE contents can provide the benefits of lower shear viscosity while maintaining the mechanical properties and surface smoothness of WPC profiles.

Strategies for Processing Wood Plastic Composites with Chemical Blowing Agents

The production of a cellular structure in wood-flour/plastic composites (WPC) is overwhelmingly dominated by the gaseous emissions/ volatiles released by the wood-flour (WF), which prevents the formation of a uniform and fine-celled structure. By adopting effective processing strategies, the adverse effects of these volatile emissions on the foam morphology of WPC can be largely suppressed. This study discusses these strategies, and presents the results obtained from extrusion processing in cases where the chemical blowing agent (CBA) predominantly controls the density reduction. The effects of CBAs on extrusion processing of WPC are discussed. All the CBAs used, produced uniform and reasonably fine-celled structures.

Critical Issues in Extrusion Foaming of Plastic/Woodfiber Composites

Foaming of wood-fiber/plastic composites (WPC) with a fine-celled structure can offer benefits such as improved ductility and impact strength, lowered material cost, and lowered weight, which can improve their utility in many applications. However, foaming of WPC is still a poorly understood art. This paper presents a review of material published, which address the various critical issues particularly in extrusion foaming of WPC, and the proposed processing techniques and strategies, for producing artificial wood with enhanced properties.

11 – Wood–polymer composite foams

Publisher Summary This chapter describes the unique advantages and applications of the Wood-Polymer Composite (WPC) foams, delineates the critical issues and processing strategies associated with the foaming of WPC, and then introduces the state-of-the-art technologies used to produce the WPC foams. WPCs made from wood fibers and polymers have been commercialized and are enjoying rapid growth in wood-replacement applications. Foaming of WPCs offers unique advantages. The physical and mechanical properties of the WPC foams are closely related to their cellular structure. Incorporating a fine-celled structure into WPCs typically is more desirable. However, a number of factors influence the WPC foam processing when WF is used. Increasing the WF content increases the apparent viscosity, which necessitates either the use of a higher Melt Flow Index (MFI) resin or the use of a lubricating additive. Use of coupling agents facilitates the dispersion and bonding of hydrophilic WF with hydrophobic resins. Suppression of the volatile emissions from the WF can be achieved by drying the WF; however, that places restrictions on the highest allowable processing temperatures, in conjunction with minimizing the residence times at those temperatures.

Effect of extrusion conditions on the surface quality, mechanical properties, and morphology of cellular wood flour/high-density polyethylene composite profiles

Wood-plastic composite (WPC) can be fine-cell processed to create a new class of low-weight composite material with improved mechanical properties that could broaden their applications. This study investigated the effects of a chemical blowing agent (CBA) and the drawdown ratio (DDR) on the surface quality, cell morphology, and mechanical properties of extruded foamed WPC profiles. The rectangular foamed WPC profiles were produced from high-density polyethylene and wood flour with different CBA contents and DDR values using a twin-screw extrusion line. The foam density, cell density, and their sizes and shapes were largely depended on the CBA content and the DDR. A foamed WPC profile with a 22% density reduction with cellular structure can be produced using an extrusion profile line.

Process Optimization through Designed Experiments to Achieve Consistency in Output Color of a Compounded Plastic Grade

ABSTRACT Plastics compounders need to understand the relationship between process variables and output color and know the optimal process conditions to achieve consistency in output. Such a relationship and optimal processing conditions are investigated for a polycarbonate resin-based plastic grade using a Box-Behnken design of response surface. This study analyzes and discusses the results of designed experiments and highlights individual and combined influences on output color of three process parameters: temperature, screw speed, and feed rate. Experimental results verify the fitness of the statistical model employed. This study suggests five sets of processing conditions ensuring consistency in output color of the plastic grade.

Effect of Mixing Intensity on Foaming Behavior of LLDPE/HDPE Blends in Thermal Induced Batch Process

ABSTRACT Linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) (with different shear thinning behaviors) were melt blended at two different compositions (10 and 25 wt%. of HDPE) and three different rotational speeds. Batch foaming process was performed over a wide range of temperatures. Bulk density measurement, cell structure evaluation, differential scanning calorimetry (DSC), and oscillatory rheology tests were performed. Results indicated the deterioration of foamability for those blended at the highest selected speed of 120 rpm. The blends mixed at a speed of 60 rpm, exhibited a slightly lower expansion ratio compared with those of mixed at a speed of 10 rpm with the same trend over the foaming temperature. For blends with 25 wt%. HDPE, proper cellular structures were obtained through a broader range of foaming temperature. GRAPHICAL ABSTRACT

Three-dimensional orientation of compression-molded high-density polyethylene/wood fibers using X-ray micro-tomography

Use of compression molding with a natural fiber-reinforced thermoplastic matrix has been growing rapidly within the last few years in various applications. Wood-reinforced high-density polyethylene offers economic efficiency, a high process reproducibility, short cycle times, a stable and high component quality, and a good recycling ability. In the present study, the distribution of fiber orientation using micro-CT scanner for compression-molded product of varying fiber content was measured, and the effects of fiber content with respect to orientation states are discussed.

Fabrication and Characterization of Electrospun PVA/Mica Fibrous Nanocomposite Mats

ABSTRACT This paper focuses on the fabrication of cost effective and high performance poly(vinyl alcohol)/mica fibrous nanocomposites using electrospinning. Effective incorporation of fine particles of mica in poly(vinyl alcohol)/mica nanocomposites was examined and confirmed along with the evidence of good dispersion, by digital optical microscopy and scanning electron microscopy. The presence of mica improved the mechanical properties of the nanocomposites without affecting the thermal stability. The electrospun poly(vinyl alcohol) mats containing 20 wt% mica exhibited tensile strength of 13.29 MPa and tensile modulus of 180.3 MPa as compared to values of 3.92 and 83 MPa, respectively, for poly(vinyl alcohol) fiber mats. GRAPHICAL ABSTRACT

Morphological Analysis of Foamed HDPE/LLDPE Blends by X-ray Micro-Tomography: Effect of Blending, Mixing Intensity and Foaming Temperature

Non-invasive x-ray micro-computed tomography was employed for thorough quantitative and qualitative analysis of the cellular structure of foams made of linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and their blends. Special emphasis was given to the differences between the results of 3D and 2D analyses, to evaluate the possible errors while studying the morphology using conventional 2D techniques (e.g. SEM). Blends with the weight compositions of 90%LLDPE/10%HDPE and 75%LLDPE/25%HDPE were produced at different rotor speeds of 10, 60 and 120 rpm and batch foaming was examined over a wide range of temperature. The void fraction values from 2D and 3D analysis were found to agree well with those obtained with the Archimedes method. Results showed more uniform cell size distribution for blends mixed at the lower spectrum of screw rotational speed. Among the blends with higher void fraction values and relatively uniform cellular structure, higher average cell size (3–30%) and cell population density (1.25–2.5 times) were noticed in 3D analysis compared with 2D data. The micro-CT images at different cross sections revealed anisotropic cell growth and more elongated cells along the thickness of the specimen. It was also observed that, with increase in foaming temperature, cell shrink prevailed over cell coalescence in the samples with lower viscosity (prepared at low rpm of 10), while for those with higher viscosity (prepared at an rpm of 60) cell coalescence was more dominant.