There is increasing number of companies producing wood-plastic composite for structural applications. However, wood plastic composite (WPC) require solving two major constraints; technique and formulation before their design value for structural application can be determined. This study focused on solving the two major constraints by employed injection moulding method to produce WPC and using different commercial available coupling agents at different percentage to produce WPC. The effect of wood to plastic ratio was also evaluated on WPC produced using the coupling agents that gave highest bending properties. Commercial polypropylene wood fine and coupling agents premixed in dumper mixer for 30 minutes prior to extrusion process at temperature of 190ºC using 110 mm counter-rotating twin-screw extruder. The WPC boards with size of 150 mm x 150 mm x 3 mm were then injection moulded by 40-ton press moulding machine. From the result, WPC produced from coupling agents Exxelor PO 1020 at 4% significantly performed better in bending properties. Further study on the effect of Exxelor PO 1020 percentage and the wood to plastic ratio showed that, WPC with 65% wood fine performed significantly better in MOR and MOE than other type of WPCs. WPC with 60% wood fine had significantly lower thickness swelling and water absorption compared to those 65% and 70% wood fine WPC. Conclusively, WPC with 65% wood fine is optimum content for WPC to produce from injection moulded method. Higher coupling agent percentage used in WPC formulation gave higher bending properties.
Over the past decade, there has been a growing interest in the development of construction and industrial products composed of wood fiber combined with thermoplastic resins. This mainly due to wood plastic composites (WPC) are renewable, less-abrasive to processing equipment, environmental friendly, low maintenance and similar as wood feature. The use of wood waste as filler make WPC promoted as environmental friendly products.
WPC and WPC process was patented in Italy around 1920s. In this process, polypropylene and wood flour were extruded to manufacture automotive interior parts. There was not much of an interest on this process until one American company implementing this Italian extrusion technology to produce automotive interior substrates (Clemons, 2002). This has followed by other companies to produce various shapes of automotive parts by extruding polypropylene and wood flour mixtures. Applications for these composites include a variety of building products, consumer, industrial and automotive. Recently, WPCs have found application areas other than automotive industry such as siding, fencing, window frames and decking. Especially after their use in decking applications, manufacturing of WPCs has seen phenomenal growth in the United States. It is well known that decking has a tremendous market in the USA with approximately 18.5 million m³ in 2000 (Winandy, 2004).
As the use of wood-plastic composite (WPC) materials extends to include more structural applications, there is an increasing need to determine design values appropriate for designing structural WPC elements. However, there are two important topics shall be clearly identify as basic approach toward WPC design value determination. The first issue shall been looking on the WPC processing method and the second issue will be specific formulation which to optimize the WPC mechanical properties to suit the general structuring application. In the first case, injection moulded method had been used for this study due to it provide higher mechanical value and reducing cellulose degradation that normally due to prolong of high temperature exposure. Then, by employ different coupling agents at certain percentages on WPC formulation, the mechanical properties of WPC can be predicted.
Many studies noted that maleic anhydride grafted synthetic polymer when used as compatibilizer, have proven to be having a bridging effect between wood filler and the polymer matrix, resulting in improvement of material mechanical properties (Lu et al., 2000; Sanadi et al., 1997). However, the molecular weight and amount of MA grafted are important parameters that determine the efficiency of the additive (Felix et al., 1993; Sanadi et al., 1995). The maleic anhydride present in the MAPP provides polar interactions such as acid-base interactions and can also covalently link to the hydroxyl groups on the lignocellulosic fiber. However, not all commercial coupling agents give the same effect on WPC performance. Some commercial coupling agents might contain other compound such as flow agent element. This element able to improve the WPC flow characteristic but the higher of this element will affect the poor performance in bending strength. Therefore, the selection of coupling agent is very important to suit to the WPC product application and processing methods requirement. Therefore, this study has two main objectives; the first objective was to evaluate the effect of different industry coupling agents on the bending properties of WPC. Whereas, second objective was to determine the effect of wood to plastic ratio on the physical and bending properties of WPC produced from industry coupling agent that gave the highest bending properties resulted from the first objective.