In 1996,210 million tons of municipal solid waste was generated in the United States. Fifty-seven million tons of this waste was recovered for recycling, 36 million tons was combusted primarily for energy recovery, and the rest (I 10 million tons) of the waste was landfilled. In 1996, plastics, rubbers, and textiles accounted for 20% by weight and 41% by volume of the total municipal solid waste. Six percent (2 million tons) of plastics, rubbers, and textiles were recovered for recycling in 1996.

Polymer-plastics technology and engineering

Extrusion processes are widely used in industries that aim to produce advanced solutions for increasingly sophisticated demands in the plastic, food, and pharmaceutical sectors. Though the process has been in use since the 1930s, limited information is available on the analytical computation of extrusion. Generally, production has been carried out based on empirical experience and trial-and-error approaches. The development of industrial operations is, however, best addressed by modelling the processes involved, and the flow of polymer melts and fibers in extruders has been subjected to some previous studies. Also included an overview of design of a die as well as challenges in sheet/film production. This article systematically and critically reviews the literature related to the process design, machine design, process parameters, flow models, and flow analysis of extrusion with a focus on modelling the extrusion of composite materials.

https://www.mdpi.com/2073-4360/12/6/1306/pdf

The Modelling of Extrusion Processes for Polymers-A Review.

Waste recycling is one of the key aspects in current day studies to boost the country’s circular economy. Recycling wood from construction and demolished structures and combining it with plastics forms wood-polymer composites (WPC) which have a very wide scope of usage. Such recycled composites have very low environmental impact in terms of abiotic potential, global warming potential, and greenhouse potential. Processing of WPCs can be easily done with predetermined strength values that correspond to its end application. Yet, the usage of conventional polymer composite manufacturing techniques such as injection molding and extrusion has very limited scope. Many rheological characterization techniques are being followed to evaluate the influence of formulation and process parameters over the quality of final WPCs. It will be very much interesting to carry out a review on the material formulation of WPCs and additives used. Manufacturing of wood composites can also be made by using bio-based adhesives such as lignin, tannin, and so on. Nuances in complete replacement of synthetic adhesives as bio-based adhesives are also discussed by various researchers which can be done only by complete understanding of formulating factors of bio-based adhesives. Wood composites play a significant role in many non-structural and structural applications such as construction, floorings, windows, and door panels. The current review focuses on the processing of WPCs along with additives such as wood flour and various properties of WPCs such as mechanical, structural, and morphological properties. Applications of wood-based composites in various sectors such as automotive, marine, defense, and structural applications are also highlighted in this review.

/pdf/a-critical-review-on-wood-based-polymer-composites-2as81d5h.pdf

A Critical Review on Wood-Based Polymer Composites: Processing, Properties, and Prospects

A review paper is presented on modeling for polymer extrusion for both single screw and twin-screw extrusion. An issue of global modeling is discussed, which includes modeling for solid conveying, melting, melt flow, and co-operation of the screw/die system. The classical approach to global modeling of the extrusion process, which is based on separate models for each section of the screw, i.e., solid transport section, melting and pre-melting sections, and the melt flow section is presented. In this case, the global model consists of the elementary models. A novel continuous concept of global modeling based on CFD (Computational Fluids Dynamics) computations is also presented, and a concept of using the DEM (Discrete Element Method) computation coupled with CFD computations is discussed.

https://www.mdpi.com/2073-4360/11/12/2106/pdf

Fundamentals of Global Modeling for Polymer Extrusion

Fused deposition modeling (FDM) is one of the most widely utilized additive manufacturing techniques by virtue of its numerous merits, such as easy operation, low cost, low energy consumption and little-to-no waste. Based on its simple configuration and extrusion-assisted process, the research and development of this technique is gradually shifting from traditional prototype printing to high-performance composite fabrication. This review provides a panorama for the recent progress of FDM technology in the manufacturing of discontinuous fiber reinforced thermoplastic composites. The entire production chain from the very beginning of FDM filament preparation to the latest stage in large-scale manufacturing process is discussed. The enlightening strategy in multi-axis FDM field is highlighted as it possesses a great potential to manufacture the next-generation composites with superior geometric complexity and flexible fiber alignment. This review also identifies the main challenges and outlook for the future development of this 3D printing technology in fiber reinforced composites.

Advances in fused deposition modeling of discontinuous fiber/polymer composites

The state-of-the-art has been presented for computer modeling of screw processing of plastics. A new generalized approach for modeling of this class of plastics processing techniques has been proposed. Single screw extrusion, twin screw extrusion, as well as injection molding are discussed. Various types of feeding machines, including flood feeding and starve feeding, are considered. An idea for a multipurpose computer system for comprehensive modeling of screw processing has been presented. A problem of optimization of screw processing has also been discussed.

Multipurpose Computer Model for Screw Processing of Plastics

An issue of modeling of twin-screw extrusion of polymeric materials is reviewed. The paper is written in honor of Prof. James L. White who was a pioneer in studying this issue. A global approach to process modeling is presented which includes solid polymer transport, polymer plasticating, and the flow of molten polymer. The methodology of CFD modeling of twin-screw extrusion is presented as well as the examples of this modeling which show the details of the process. Optimization and scaling of twin-screw extrusion are also covered. And finally, the future prospects of developments and research of twin screw extrusion is discussed.

/pdf/modeling-of-twin-screw-extrusion-of-polymeric-materials-2tgimt05.pdf

Modeling of Twin Screw Extrusion of Polymeric Materials

An experimental study of the polymer behavior in a starve-fed single screw extrusion is presented. Various polymeric materials, semicrystalline low density polyethylene (LDPE), polypropylene (PP), and (LDPE/PS) polyblends were investigated at various operating conditions. A “screw pulling-out” technique was used to study polymer behavior along the screw. The solid conveying, melting position, the extent of starvation, and the fully filled regions were observed. Polymer samples were stripped off from the screw which was removed from the machine to investigate melting mechanism. It was seen that filling of the screw channel increases with the flow rate at a fixed screw speed, and decreases with the screw speed at a fixed flow rate. Contiguous solids melting mechanism was observed for flood fed extrusion, but it was not observed for starve-fed extrusion. A new two-stage physical model of polymer melting has been proposed with conductive mechanism for melting in the starve-fed region and dispersed melting mechanism in the fully filled region. Melting action seems to be faster for starve feeding than for flood feeding, since the pellets are not compacted into a dense solid bed. It was observed that the pressure and power consumption considerably decrease with starvation. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Experimental study for starve‐fed single screw extrusion of thermoplastics

A composite simulation model of solids conveying, melting and melt flow in a closely intermeshing counter-rotating twin-screw extruder has been developed. The model is based on combining new melt conveying models with melting and solids conveying models, and the die is included into considerations. A general approach is applied using fully three-dimensional non-Newtonian FEM modeling for melt conveying to develop screw pumping characteristics which are implemented into the composite model. Several screw configurations are considered including non-classical elements. Computations are made for axial fill factor, pressure, temperature, and melting profiles. The results are validated experimentally. POLYM. ENG. SCI., 2015. © 2015 Society of Plastics Engineers

A composite model for an intermeshing counter-rotating twin-screw extruder and its experimental verification

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