Development of Biocomposite Wall Cladding from Kenaf Fibre by Extrusion Molding Process K. Abdan1,a, E.S. Zainudin1,b, A.R. Mohd. Faizal2,c, H. Jalaluddin1, A.H. Umar1,d and W.N.W.N Syuhada1,e 1
Institute of Tropical Forestry and Forest Product, Universiti Putra Malaysia, Selangor, Malaysia 2
Radiation Processing Technology Division, Malaysian Nuclear Agency, Selangor, Malaysia a
[email protected],
[email protected],
[email protected], d
[email protected],
[email protected]
Keyword: Extrusion Molding, Kenaf-Plastic Composite, Polypropylene, Mechanical Properties, Kenaf
Abstract. Nowadays, natural fibre-thermoplastics composites (NFPC) are replacing the conventional wood and timber due to its lower cost, avoid deforestation, higher strength-to-weight ratio and resistant to termites. These composites can be utilized for non-structural components of a building system such as decking, wall cladding, floor tiles and window frame. A natural fiber/plastic composite was produced by extrusion molding process to create a wall cladding profile. The raw materials used for the composites are 40% kenaf fibre and 60% polypropylene (PP). These materials were compounded through a twin-screw extruder and then cut into pellets. The moisture content found in the kenaf/PP composites (KPC) pellets was 2.89%. Therefore, the pellets required to be oven dried every time right before entering the hopper of the extruder. The temperature along the barrel was set to 180°C and the die head temperature is set to 165°C. At the end of the extrusion molding process, pressurized air was used for cooling the profile. Then, samples of the wall cladding were taken back to the laboratory for product quality assurance. Measurements of the samples show that the product experiences 3% of shrinkage in term of width and 1% of shrinkage in term of thickness. Water absorption test indicates an increase of 13.6% of weight after 24 hours immersion of water. Impact strength test was also conducted on the wall cladding samples and the mean result was 2.55 kJ/m². Tensile test on the extruded KPC product indicates a low tensile strength at 4.51 MPa and tensile modulus of 205.01 MPa. The sample also proven to be light weight as the density of the material was found to be 0.618g/cm³. Introduction Natural fibres such as jute, kenaf, pineapple leaf, oil palm empty fruit bunch, sugar palm, sisal, rice husk, sugarcane bagasse and other ligno-cellulosic fibres have been used as fillers or reinforcement in plastic composites. The advantages of this type of fibres are it is abundance, easy to obtain, low cost, part of plants that are not use and thrown away, not abrasive hence avoid damaging machines and molds during fabrication process, prevent deforestation by reducing the dependency on wood, sustainable and can be replant [1,3]. Studies on fibres derive from agricultural sources are advancing to make use of lingo-cellulosic fibres in replacing synthetic fibres as reinforcing fillers. Kenaf is a member of hibiscus family which is a biodegradable and environmentally friendly crop. It has been found to be important source of fiber for composites and other industrial application. Kenaf have excellent properties for reinforcing plastic composites as it has low density, no abrasion during processing, high filling levels, high specific mechanical properties and biodegradability. Kenaf, as compared to other non-wood fiber, is found to be comparatively higher in tensile strength [2], cheaper, sustainable as well as environmentally friendly. Extrusion molding can be applicable in KPC processing, specifically for products that have continuous body such as beam, wall cladding and flooring. The single screw extruder is a common extrusion system for producing plastics or plastics composites profiles. The raw material will be fed
into the hopper at one end of the barrel and the product will go out through an orifice (die head) at the other end of the barrel (refer with: Fig. 1). The purpose of this research is to determine the feasibility of producing a biocomposite wall cladding from kenaf fibres and polypropylene.
Die head orifice
Air coolant
KPC extrudate
Figure 1: The KPC wall cladding outgoing the die head orifice. Methodology Material Preparation. Kenaf stems were collected from Lembaga Tembakau Negara planted in Terengganu, Malaysia. The variety name called V36. The polypropylene (PP) pallet was purchased from Polypropinas Sdn Bhd (Malaysia). Kenaf stem was cut into chips size between 3 cm to 5 cm length. In this study about 100 kg of kenaf chip was pulverized into powder form and screened to obtain 150µm fibre size. KPC Pellets Preparation. PP pellets were mixed thoroughly with 3% maleic anhydride grafted polypropylene (MaPP) pellets by using a rotating mixer that runs for 30 minutes. In producing the KPC pellets, a twin screw extruder which has a main feeder and one additional side feeder was used. The PP/MaPP pellets were placed into the main feeder at the end of the extruder barrel, while the kenaf fibres were placed into the side feeder. The speed of the feeders was calibrated to achieve 40 wt% of kenaf and 60 wt% of polymer. Finally, the pelletizer cuts the compounded KPC into pellets (refer with: Fig. 2 and 3). The KPC pellets were then examined to detect the level of moisture content. KPC compound
Figure 2: The extruded KPC compounds cooled by water bath.
Pellets
KPC compound
Figure 3: Pelletizer cuts the KPC compounds into pellets.
Extrusion Molding Process of Wall Cladding. A single screw extruder was used to produce the kenaf biocomposite wall cladding. Prior to the process, KPC pallets were oven dried for 24 hours at 60ºC to reduce moisture in the material. Extra additive such as zinc stearate pellets (0.5% by weight) was added together with KPC pellets for lubrication during processing by reducing adhesion of the plastic melt to the metal surface. The die head for wall cladding profile was installed on the extruder. Heating in the extruder barrel consists of three temperature zone. While, the die head temperature is controlled by one heater. The temperature in the extruder barrel must be set within the range of the melting point of polypropylene (171ºC) but lower than the degradation
point of kenaf fibres (210ºC). After four trials running the extruder for KPC wall cladding, the optimum temperature setting across the extruder is as shown in table 1: Table 1: Temperature setting for extrusion process of wall cladding Set Temperature
Zone 1 180ºC
Zone 2 180ºC
Zone 3 180ºC
Die head 166ºC
Determining Physical and Mechanical Properties. The wall cladding profiles were taken back to laboratory for physical and mechanical testing (refer with: Fig. 4). Dimensions of the sample were recorded and compare with the original design (thickness: 6mm x width: 80mm) to identify any shrinkage. Water absorption experiment (according ASTM D570) was conducted to analyze the water uptake after 24 hours immersion. The density of the extruded KPC wall cladding was also measured. The mechanical properties of the product were also tested by determining impact strength (according ASTM D256) and tensile strength and tensile modulus (according ASTM D638-type I).
(a)
(b)
Figure 4: (a) KPC wall cladding and (b) Tensile specimen following ASTM D638-type (i) Result and Discussion Moisture Content of KPC pallets. The KPC pellets were weighted before and after oven dry (105ºC for 24 hours). The weight difference shows that the pellets have moisture content (MC) of 2.89%. Generally materials derive from natural fibres which is hydrophilic will absorb water easily from atmosphere, typically from humid climate such as Malaysia. The MC is considered high for extrusion process, because moisture will cause the product to have crimple texture on product surface as proven by earlier trials. Beside that other researchers [4] found that the percentage of moisture uptake increased as the fibre volume fraction increased due to the high cellulose content. Since the fibre loading used in this study was 42% (approximately 50% volume fraction) the MC result was expected. Therefore, to overcome this condition the pellets were required to be oven dried at temperature of 60 ºC for 24 hours to obtain less than 0.5% MC prior entering the extruder KPC Profile Shrinkage. The design of the wall cladding has the width of 80mm and thickness of 6mm. After the KPC wall cladding extruded and cool down, measurements shows that samples tend to shrink to an average thickness of 5.94mm and average width of 77.6mm with shrinkage percentage of 0.01% for thickness and 0.3% for width. Possible explanation for this situation is due to thermal expansion. Thermoplastic composite materials are generally shaped at elevated temperature and then cooled. Since in most cases the thermal expansion coefficients of polymers are much greater than reinforcement fibres this cooling process results in compressive radial stress
σr at the interphase [5]. Therefore, designers should consider the tolerance in width and thickness and width around ± 0.01 to 0.3mm of KPC material before designing a mold. Density of KPC Profile. The extruded KPC wall cladding has an average density of 0.618g/cm³. The samples have lower density than liquid water and tend to float. Therefore, a weight must place upon the samples to keep it immerse during water absorption test. The porosity can clearly be observed by SEM micrograph at the fractured area of the KPC wall cladding (refer with: Fig.5). Porosity causes the product to become lightweight but loses it mechanical strength. Compare to injection molding, extrusion process does not have a closed mold, therefore no pressure exist to compact the KPC material. Other than that, the surface of the product is rough due to friction against the die head orifice during extrusion process (refer with: Fig.6).
Figure 5: SEM micrograph at the fractured area of the KPC wall cladding
Figure 6: SEM micrograph at the surface of the KPC wall cladding
Water Absorption Test. Water absorption test indicates an increament of 13.6% of weight after 24 hours immersion in distilled water. The porosity of the material discussed earlier is the reason for the high water uptake. Other than that, natural fibres such as kenaf are hydrophilic which prone to absorb water. In addition all polymer composites absorb moisture in humid atmosphere and when they are immersed in water. The effect of moisture absorption leads to the degradation of fibrematrix interface region which thus creates poor stress transfer efficiencies resulting in a reduction of mechanical properties [6,7]. Meanwhile, among the main concerns for the use of natural fibre reinforced composite materials are their susceptibility to moisture absorption and the effects on the physical and mechanical properties [8]. Mechanical Properties. Impact strength test was conducted on the wall cladding samples and the mean result was 2.55 kJ/m². Other than that, tensile strength test on the extruded KPC product indicates a low tensile strength at 4.51 MPa and tensile modulus of 205.01 MPa. Previous studies using the similar KPC formulation but by compression molding shows a higher tensile stress (22.95 MPa) and higher tensile modulus which is 320 MPa (refer with: Table 2) [9]. Due to extrusion process, the KPC become less dense and lost its mechanical properties. It might also contribute to the porosity behavior and high MC of the KPC as mentioned earlier. Table 2: Effect of processing method to mechanical properties of KPC Tensile Strength [MPa]
Tensile Modulus [MPa]
Impact Strength [kJ/m²]
Compression Molding
22.95
320
-
Extrusion Molding
4.51
205
2.55
Processing Method
Future Work The fabrication of this KPC wall cladding is still in progress. There are biocomposite manufacturers that successfully achieve in producing a high quality NFPC product by extrusion process, thus it is possible to improve the physical and mechanical strength of the wall cladding and its aesthetic appearance. Upgrades of the extruder such as adding a motorized puller at the end of the conveyer to pull the wall cladding at constant speed may help to increase the tension of extruded profile and consequently increase the tensile strength. Moreover it is suggested to add conditional roller in order to avoid the profile in uneven shape like crumple. By installing a bakelite plate divider in between of die head heater will permit to isolate heat zone and controlling the processing temperature. All this countermeasure will be implement in the near future. Summary Overall, the development of kenaf/polypropylene composite for wall cladding application requires reassessment and improvement. The mechanical strength of the product is considered low compare to compression molding method. Flaws such as high porosity, bending extrudate profile and high surface roughness need to be eliminated. Improvements of KPC wall cladding will be made according the proposed future work mention above. Acknowledgements The author would like to thankful the Institute of Tropical Forestry and Forest Products (INTROP) grant EPUP01-01 for the sponsorship of this project. The author also likes to wish highly appreciation to Biocomposite Technology Laboratory technical staff. His assistance is much valuable in the successful of this study.
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