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Über dieses Buch

Wood-plastic composite (WPC) is a non-recyclable composite material lumber or timber made of recycled plastic and wood wastes which has become one of the most dynamic sectors of the plastics industry in this decade. It is used in numerous applications, such as, outdoor deck floors, railings, fences, landscaping timbers, park benches, window and door frames. This book starts with a brief glimpse at the basic structures and properties of WPCs. Aspects such as surface treatment, machinery used and testing types of WPCs are also covered. The following chapters of the book give a view of foam technology, flame retardant properties and colour retardant properties of WPCs. The way morphology affects or controls the physical and mechanical behaviours of the finished materials is discussed. Finally, the authors give an overview of the applications of wood-plastic composites in daily life. The book may serve as a source book for scientists wishing to work in this field.



Chapter 1. Overview of Wood-Plastic Composites and Uses

A composite material is made by combining two or more materials to give a unique combination of properties. The above definition is generic and can include metal alloys, plastics, minerals, and wood. Fiber-reinforced composite materials differ from the above materials in that the constituent materials are different at the molecular level and are mechanically separable. In bulk form, the constituent materials work together but remain in their original forms. The final properties of composite materials are better than constituent material properties.
The concept of composites was not invented by human beings; it is found in nature. An example is wood, which is a composite of cellulose fibers in a matrix of natural glue called lignin. The shell of invertebrates, such as snails and oysters, is an example of a composite. Such shells are stronger and tougher than man-made advanced composites. Scientists have found that the fibers taken from a spider’s web are stronger than synthetic fibers. In Korea, India, Greece, and other countries, husks or straws mixed with clay have been used to build houses for several 100 years. Mixing husk or sawdust in a clay is an example of a particulate composite and mixing straws in clay is an example of a short fiber composite. These reinforcements are done to improve performance.
Jin Kuk Kim, Kaushik Pal

Chapter 2. Surface Modifications in WPC with Pre-Treatment Methods

Compared with conventional and mineral filler reinforced thermoplastic products, wood–polymer composites (WPC) have many advantages such as high specific strength and modulus, low cost, low density, and low friction during compounding. Unlike wood, WPC have excellent dimensional stability under moisture exposure [1, 2] and better fungi and termite resistance [3, 4]. For WPC, one of the most attractive features is that it can help recycle thermoplastic and wood wastes. Therefore, WPC have developed quickly in the last three decades [5]. However, polar wood fiber and non-polar thermoplastics and commodity plastics like PE, PP are not compatible, thus resulting in poor adhesion resulting in weak interface. [68].
Jin Kuk Kim, Kaushik Pal

Chapter 3. Process and Machinery Used for WPC

The feature common to all polymeric composite processes is the combining of a resin, a curing agent, some type of reinforcing fiber, and in some cases a solvent. Typically, heat and pressure are used to shape and “cure” the mixture into a finished part. In composites, the resin acts to hold the fibers together and protect them, and to transfer the load to the fibers in the fabricated composite part. The curing agent, also known as hardener, acts as a catalyst and helps in curing the resin to a hard plastic. The reinforcing fiber imparts strength and other required properties to the composite.
Jin Kuk Kim, Kaushik Pal

Chapter 4. Recent Past about WPC Work

In recent years, significant efforts have been made to manufacture thermoplastic composites using such natural fibers as wood sawdust, wheat straw, nut shell fiber, and jute fiber [13]. The rationable behind these efforts is that the use of natural fibers offers several benefits, including low cost, high specific properties, renewable nature, and biodegradability. Wood fibers are the most favored form of fibers in commercial usage. Because of their high specific stiffness and strength, Wood-fiber/Plastic Composites (WPCs) are a cost-effective alternative to many plastic composites or metals [4]. Wood fiber is a non-abrasive substance, which means that relatively large concentrations of this material can be incorporated into plastics without causing serious machine wear during blending and processing. In spite of their higher price, WPCs are becoming increasingly acceptable to consumers as a replacement for natural wood due to such advantages as durability, color permanence, resistance to degradation and fungal attacks, and reduced maintenance. Furthermore, adding wood fibers to plastic products makes good use of waste wood. WPCs are mainly employed in building products, such as decking, fencing, rails, door and window profiles, and decorative trims. Moreover, these composites are also gaining acceptance in automotive and other industrial applications [5].
Jin Kuk Kim, Kaushik Pal

Chapter 5. Effect of Compatibilizers in WPC Composites

Wood-fiber (WF) filled plastic composites (WPC) have gained rapid growth in recent years. Such materials offer significant advantages, which justify their use. Wood fiber is obtained from natural resources, it is available in various forms in large quantities, light, cheap, and it can be added to commodity matrices in considerable amounts thus offering economically advantageous solutions [14]. The main drawbacks of such composites are their poor adhesion to basically all matrix polymers [5, 6] and high density compared to natural wood and certain plastics [7].
Jin Kuk Kim, Kaushik Pal

Chapter 6. Flammability in WPC Composites

Wood fiber reinforced plastic composites represent an emerging class of materials that combine the favorable performance and cost attributes of both wood and thermoplastics [1]. In comparison to other fillers, the natural and wood fiber reinforced polymer composites are more environmentally friendly, and are used in transportation, military applications, building and construction industries, packaging, consumer products, etc. [2].
Polypropylene (PP) has been widely used for production of natural fiber/polymer composites because of its low density, high water and chemical resistance, good processability, and high cost–performance ratio [36]. Due to the poor compatibility between natural fibers and PP matrix, a compatibilizer can be added to improve adhesion between matrix and fibers leading to enhancement of mechanical properties of composites. A prominent method represents the addition of maleic anhydride polymers as compatibilizers, e.g., maleic anhydride-grafted poly(propylene) (PP-g-MA) and poly(styrene)-blockpoly (ethene-co-1-butene)-block-poly(styrene) triblock copolymer (SEBS-g-MA) [48].
Jin Kuk Kim, Kaushik Pal

Chapter 7. Expanded Wood Polymer Composites

Foamed solid polymers, also referred as microcellular composites or expanded composites or sponge materials are a class of materials that are extensively used in everyday applications from the foamed polyurethane mattress we sleep onto the polystyrene based Styrofoam cup in which we have our morning coffee. According to some estimates, the market of foam products in the world stands at 14 billion US Dollars and is expected to grow at a phenomenal rate of 14% for the next 5 years. This growth will be largely triggered by phenomenal demand of China who in recent times accounts for 26% of world’s polystyrene and 34% of polyurethane foam world’s consumption. Several polymers can be foamed to desired low densities to suit applications based on properties such as weight reduction, insulation, buoyancy, energy dissipation, convenience and comfort characteristics like cushioning factor etc.
Jin Kuk Kim, Kaushik Pal

Chapter 8. Wood Plastic Composite Foam Applications

Wood fiber/plastic composites (WPCs) utilize fibers as reinforcing filler in the polymer matrix and are known to be advantageous over the neat polymers in terms of the materials cost and mechanical properties such as stiffness and strength. Wood fiber reinforced polymer composites are microcellular processed to create a new class of materials with unique properties. Most manufacturers are evaluating new alternatives of foamed composites that are lighter and more like wood. Foamed wood composites accept screws and nails like wood, more so than their non-foamed counterparts. They have other advantages such as better surface definition and sharper contours and corners than non-foamed profiles, which are created by the internal pressure of foaming. The microcellular wood fiber reinforced polymer composites can be obtained by different processes (batch, injection molding, extrusion, and compression molding process) by using physical or chemical foaming agent.
Jin Kuk Kim, Kaushik Pal

Chapter 9. Conclusions

Wood, plastic and the uses of these composites in our daily life has been described in first chapter followed by the surface treatment and additives used for preparation of wood–plastic composites in subsequent chapter.
In the third chapter, machinery and testing techniques for making of wood–plastic composites has been discussed. Because, the authors think that proper machinery is the main important part to produce a good quality WPC. Fourth chapter is described about the research work done by other researchers in recent past.
One of the objectives of this research is to achieving the effects of screw configuration, screw speed, silica content and various compatibilizer on the physico-mechanical and foaming properties of wood-fiber/PP composites. Wood-fiber/PP composites were produced on the intermeshing co-rotating twin screw extruder. Microcellular closed cell wood-fiber/PP composite foams were prepared using pressure-quench batch process method. First, an attempt has been made to determine the optimum conditions of extrusion that involve are screw configurations, screw speed. The experimental results showed that wood-fiber/PP composite prepared under the configuration C (Fig. 5.​1) at screw speed of 150 rpm have higher mechanical properties and narrower cell size distribution, due to the improved dispersion of the wood-fiber in the composites. And then, the effect of the silica content on properties of wood-fiber/PP/silica composites showed that the relationship between silica content and mechanical properties was obvious. The property enhancements were controlled mainly by the extension of silica agglomeration. The foam density is governed by the combined effect of cell nucleation, cell growth, and cell coalescence, as a nucleation agent, the silica in wood-fiber/PP composite created a large amount of heterogeneous nucleation sites during foaming. The heterogeneous nucleations increased the cell density and decreased the cell size and foam density. This phenomenon disappears at high content of silica due to big agglomerates. Finally, the results of physico-mechanical properties of wood-fiber/PP composite with various compatibilizer showed that the PP-g-MA and SEBS-g-MA enhanced adhesion between the WF and PP matrix, Wood-fiber/PP composite with addition of PP-g-MA as compatibilizer showed highest tensile strength and stiffness. Composites with SEBS-g-MA showed the higher impact strength, elongation at break and tensile strength compared to composite systems with SEBS. The batch foaming result of PP/WF composites with various compatibilizer showed relationships between cell morphology and their crystallinity and stiffness. Higher crystallinity, showed higher stiffness and higher relative density.
Jin Kuk Kim, Kaushik Pal


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