Rotational Molding of Flax Fiber Reinforced Thermoplastics
Paper No: MBSK 02-209 An ASAE Meeting Presentation
Rotational Molding of Flax Fiber Reinforced Thermoplastics J. Ward¹, S. Panigrahi¹, L.G. Tabil¹, W.J. Crerar ¹, T. Powell¹ ¹Department of Agricultural and Bioresource Engineering University of Saskatchewan 57 Campus Drive, Saskatoon, SK. S7N 5A9 CANADA Abstract: Flax fibers are being combined with thermoplastic materials then rotationally molded into useful products. Flax fibers are very strong and this property is being added to the composite parts. Using flax fibers with linear low-density polyethylene thermoplastic reduces the mass of the biocomposite due to its low density, increases its stiffness and also reduces the final product costs. Some of the problems that need to be overcome are the processing of the biocomposites, weight percentages of fiber in biocomposites, fiber cutting and mixing in thermoplastic resin. Rotational molding is a different process and one that has not been studied in depth. This paper describes the process of rotational molding composite parts and some of the problems that were encountered. Keywords: Flax fiber, biocomposite, thermoplastic, tensile strength, rotational molding The author(s) is solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of ASAE, and its printing and distribution does not constitute an endorsement of views which may be expressed. Technical presentations are not subject to the formal peer review process by ASAE editorial committees; therefore, they are not to be presented as refereed publications. Quotation from this work should state that it is from a presentation made by (name of author) at the (listed) ASAE meeting. EXAMPLE – From Author’s Last Name, Initials. “Title of Presentation.” Presented at the Date and Title of meeting Paper No. X, ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659 USA. For information about securing permission to reprint or reproduce a technical presentation, please address inquiries to ASAE. ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659 USA Voice: 616-429-0300 Fax: 616-429-3852 E-Mail:
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Rotational Molding of Flax Fiber Reinforced Thermoplastics J. Ward, S. Panigrahi, L.G. Tabil, W.J. Crerar , T. Powell Introduction The usage of flax fibers as an additive in the plastics industry makes both environmental and economic sense. The possibility of a booming new industry for cash strapped flax growing farmers is possible. Currently the flax crops grown in Canada are almost solely grown for the seed. The fiber is a byproduct that has virtually no bonus to the farmer. It is a byproduct that is commonly burnt in the field after the seed has been collected. This is an obvious environmental concern as pollution increases with burning, and it takes both time and money for the farmer to conduct the burning. The potential for this environmental and economic burden to be overcome is a real possibility, (Liu it al.1995). More testing and work must still be done on adding short flax fibers to plastic materials to make viable flax fiber biocomposite products. What we are investigating is the whole processing stage of the fiber to usage of rotationally molded thermoplastic biocomposites. This involves finding a feasible cutting method, chemical treatments, weight percentages, blending techniques and composite testing. Flax fibers can be used as reinforcing filler over environmentally unfriendly glass fibers, can be modified to obtain desired mechanical properties and reduce the usage of petroleum-based plastics, (Burger et al. 1995). Flax fibers are currently being used in many diverse products. Automotive, building, and recreational industries are steadily increasing the usage of these fibers as a cost saving measure that is non-abrasive to processing machinery. Biocomposite products, besides being cost effective and environmentally friendly, are recyclable, have better acoustics and have good thermal insulation. When these biocomposites are rotationally molded many different shapes and colors can be achieved. The main impediment that is still to be overcome is that the farming and plastics industry do not currently have the infrastructure to build large quantities of composites materials. At the farming end, very few bulk handling and processing facilities currently exist for fibrous materials. These facilities should, once built, be located in rural areas where transportation costs are minimized, large scale cutting can occur and chemical treatments can be achieved. In other words it has the potential to be one of the few large value-added farming applications here in Saskatchewan and many agricultural centers. The plastics industry however can very easily start large-scale manufacturing of biocomposites. Blending of the materials and handling the fibers are the main areas of concern. Fortunately rotational molding machines do not need any adaptations for incorporating flax fibers into the process stream. Flax fibers are hygroscopic in nature, the fibers absorb or release moisture depending on the environmental conditions. Moisture absorption causes swelling of the
2
fibers that can lead to dimensional instability of the biocomposite, and reduction in some mechanical properties. Chemical treatments of the fiber can help stop this absorption process, (Panigrahi et al. 2002). Another problem associated with using flax fiber reinforcement is that the final product may have a distinct odor. Rotational Molding Process The rotational molding machine used for this work is located at Parkland Plastics in Saskatoon, Saskatchewan, Canada. It is a carousel-type molding machine that has four separate arms that can each rotate about two separate axes. By following the process of one of the four arms, it becomes easy to see how it is more of a four stage process that maximizes finished product quantity. The first arm is a loading arm where the mould cavities are filled, clamped and prepared. The arm at this stage is not being rotated. This arm then moves into the heating area where a galvanized steel shell houses the rotating arm. In this shell, the product is heated to 250°C until the material starts to melt and stick to the inner surface of the mold cavity. When the material has thoroughly melted and built a uniform layer over the inner mould cavity surface it is then moved into a cooling chamber while under constant rotation. If the arm stops rotating an this stage, the molten material will be affected by gravity and pool at the bottom of the cavity. The cooling chamber is the arms third stage and is where the material hardens into its final shape. Forced air is blown over the mould cavities to increase cooling rates. The fourth and final stage is the unloading stage where the finished product is further cooled with the mold lids off then removed. Figure 1 below shows how this process works.
Figure 1. Four stages of rotational molding 3
This particular machine at Parkland Plastics can be adjusted for many different applications. Single large mold cavities can be placed on each arm or many smaller shapes. The individual arms can also be adjusted for rotation, and heated at varying temperatures depending on the desired application. Table 1 below highlights some of the advantages and disadvantages of using a rotational molding machine. Table 1. Advantages and disadvantages of rotational molding
Advantages
Disadvantages
Molds are simple and inexpensive (low Labour intensive (loading and unloading) pressure) Molds of different size and shape can be Not suited to large production runs of small used on same equipment parts Good wall thickness uniformity Products can be almost stress free Material The plastic material being used in the preliminary testing is linear low-density and high-density polyethylene. The flax fiber is the linseed variety grown in Saskatchewan and decorticated on a standard scotching mill. The fiber was cut in 2 to 5 mm lengths before addition to the composite. So far, flax fiber is the only reinforcement material being tested, however hemp fibers are a potentially viable alternative. It is available in bulk quantities at very cheap prices near the research facility. Table 2 and 3 show how flax fiber compares to other fibers, both agricultural and man-made. Table 2 is the compositions of agricultural fibers and Table 3 is a comparison with man made E-glass fibers used extensively in the plastics industry. Table 2. Comparison of natural fiber compositions, (Panigrahi et al. 2002)
Fiber
Cellulose
HemiCellulose
Pectin/Lignin Wax
Flax Hemp Jute Sisal
64.1 67.0 64.4 65.8
13.7 16.1 12.0 12.0
3.8 4.1 12.0 10.7
1.5 0.7 0.5 0.3
4
Table 3. Glass fiber properties compared to flax fiber, (Panigrahi et al. 2002)
Properties
Flax
E-glass
Density (g/cm³) Tensile Strength (MPa) E-Modulus (GPa) Specific (E/density) Elongation at Failure (%) Moisture absorption (%)
1.5 800-1100 40-100 26-66 1.2-1.6 7
2.55 2400 73 29 3 -
Cutting A cutting machine is currently being developed at the Agricultural and Bioresource Engineering department at the University of Saskatchewan. The requirements for the machine when done will be to cut the high strength fibers into short 2 to 5 mm lengths, be able to process large quantities of fiber daily and to be as inexpensive as possible. The initial work is looking at using a rotating blade to cut the fibers against a shear bar. Some problems being encountered are keeping the cutting blades as close as possible to the shear bar in order to cut the material and not bend it. Another problem is a collection system that is capable of retaining the short fibers. If the machine is to be used inside this is a necessity. Chemical Treatments Preliminary work is also being conducted on how to chemically treat the fibers before being processed into the biocomposite. It is known that chemical treatments can decrease the water absorption of the fibers, clean the fiber surface, chemically modify the surface or increase the surface roughness in order to increase the interface adhesion between the fiber and the matrix, (Yuan et al. 2001). Some of the chemical treatments currently being used are the plasma treatment technique and immersion in a 5 % NaOH solution for 24 hours. However other methods are also available. This chemical treatment step can be seen as a necessary hindrance to the biocomposite process. Treatment facilities will have to be built that can treat large quantities of fiber. It makes economic sense to build these facilities along with the cutting facilities, hopefully where the fibers are grown to increase the economic potential for rural areas. However, depending on the treatment method used, these facilities will have to manage the wastes created from these processes. Some of the treatment methods use harmful chemicals that have to be handled in an environmentally safe fashion.
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Blending Blending of the plastic and the fiber is a very important component in biocomposite processing. This is one of the main challenges in rotational molding. Initial testing was done by mixing the fiber and plastic powder with a simple drill and mixing attachment but the inner surface of the molded material can have a build up of fiber if this is the only mixing step. The bulk density of thermoplastics is in the 500 to 600 kg/m³ range, while uncompressed lignocellulosic material is in the 50 to 250 kg/m³ range. This can lead to a poor mix depending on the rotational speeds used and the melting temperatures applied. Further research will involve using a screw extruder to mix the materials and pelletizing them. This extruder will also be used to conduct testing on how the fibers can be aligned in the matrix. The strength of the biocomposite can vary greatly depending on how the fibers are orientated. Initial testing has been conducted using only random orientation of the fibers, (Panigrahi et al. 2002). Weight Percentage of Fiber The weight percentage of fiber in the composite can be altered to suit individual product needs. If more fiber is added the tensile strength of the composite increases, or if more friction is needed the fiber content can also be increased. An application for increased friction is in steps or stairs on home decks. The fiber content can also be decreased if the final product is to be used in extremely moist environments. This will help insure that shrinking and swelling of the product will be reduced. Figure 2 below shows the relationship of fiber weight percentage versus tensile strength. Tensile testing was conducting by cutting biocomposite samples into dumbbell shapes them pulling to the break point.
6
Fiber weight VS Tensile Strength 24 Tensile Strength, (MPa)
22 20 18 16
LDPE-Flax Fiber Composite
14 12 10 0
10
20
30
40
Fiber wt. %
Figure 2. Tensile strength of flax fiber-LDPE biocomposite Conclusion Flax fiber has a very promising future in the rotational molding industry. Plastic manufacturing is one of the few billion dollar industries, and flax fibers have the potential to break into this lucrative industry. The research we are conducting at the University of Saskatchewan will hopefully speed up or enhance the fibers potential. One of the main points of this research is that it is intended to help the flax growers and rural areas in particular. Saskatchewan farmers are currently undergoing a severe drought coupled with very low commodity prices. The flax fiber is already being produced and can be obtained relatively cheap compared to glass fiber reinforcements. Table 4 below highlights some of the advantages and problems of using flax fibers compared to glass fibers. Table 4. Advantages and problems with using flax fiber in biocomposites
Positives
Problems
Obtained Cheaply High strength Lightweight (Low Density) Environmentally Friendly Non-Abrasive to Machinery High Stiffness Good Acoustics
Absorbs Moisture Need Chemical Treatments Need Processing Infrastructure Odorous
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References Burger, H., A. Koine, R. Maron, K-P. Meick.1995. Use of natural fibres and environmental aspects. International Polymer Science and Technology. 22: 25-34. Panigrahi, S., L. G. Tabil., W. J. Crerar, S. Sokansanj, J. Ward, T. Powell, A. J. Kovacs, L. Braun. Application of Saskatchewan grown flax fiber in rotational molding of polymer composites.2002. Presented at AIC 2002 Meeting SCAE/SCGR Program. Saskatoon, Sk, Canada. July 14-17, 2002. Morton, W. E. and J. W. S. Hearle.1993. Physical properties of textile fibres, 3rd edn. The Textile Institute. Felix, J. M., P. Gatenholm.1991. The nature of adhesion in composites of modified cellulose fibres and polypropylene. Journal of Applied Polymer Science. 42: 609-620. Yuan, Xiaowen., K. Jayaraman, D. Bhattacharyya.2001. Plasma treatment of sisal fibres and its effect on tensile strength and interfacial bonding. Presented at the Third International Symposium on Polymer Surface modification. Newark, New Jersey, USA. May, 2001. Sanadi, A. R., S. V. Prasad, P. K. Rohatgi.1985. Natural fibres and agro-wastes as fillers and reinforcements in polymer composites. Journal of Scientific and Industrial Research. 44: 437-442.
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Rotational Molding of Flax Fiber Reinforced Thermoplastics J. Ward¹, S. Panigrahi¹, L.G. Tabil¹, W.J. Crerar ¹, T. Powell¹ ¹Department of Agricultural and Bioresource Engineering University of Saskatchewan 57 Campus Drive, Saskatoon, SK. S7N 5A9 CANADA Abstract: Flax fibers are being combined with thermoplastic materials then rotationally molded into useful products. Flax fibers are very strong and this property is being added to the composite parts. Using flax fibers with linear low-density polyethylene thermoplastic reduces the mass of the biocomposite due to its low density, increases its stiffness and also reduces the final product costs. Some of the problems that need to be overcome are the processing of the biocomposites, weight percentages of fiber in biocomposites, fiber cutting and mixing in thermoplastic resin. Rotational molding is a different process and one that has not been studied in depth. This paper describes the process of rotational molding composite parts and some of the problems that were encountered. Keywords: Flax fiber, biocomposite, thermoplastic, tensile strength, rotational molding The author(s) is solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of ASAE, and its printing and distribution does not constitute an endorsement of views which may be expressed. Technical presentations are not subject to the formal peer review process by ASAE editorial committees; therefore, they are not to be presented as refereed publications. Quotation from this work should state that it is from a presentation made by (name of author) at the (listed) ASAE meeting. EXAMPLE – From Author’s Last Name, Initials. “Title of Presentation.” Presented at the Date and Title of meeting Paper No. X, ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659 USA. For information about securing permission to reprint or reproduce a technical presentation, please address inquiries to ASAE. ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659 USA Voice: 616-429-0300 Fax: 616-429-3852 E-Mail:
1
Rotational Molding of Flax Fiber Reinforced Thermoplastics J. Ward, S. Panigrahi, L.G. Tabil, W.J. Crerar , T. Powell Introduction The usage of flax fibers as an additive in the plastics industry makes both environmental and economic sense. The possibility of a booming new industry for cash strapped flax growing farmers is possible. Currently the flax crops grown in Canada are almost solely grown for the seed. The fiber is a byproduct that has virtually no bonus to the farmer. It is a byproduct that is commonly burnt in the field after the seed has been collected. This is an obvious environmental concern as pollution increases with burning, and it takes both time and money for the farmer to conduct the burning. The potential for this environmental and economic burden to be overcome is a real possibility, (Liu it al.1995). More testing and work must still be done on adding short flax fibers to plastic materials to make viable flax fiber biocomposite products. What we are investigating is the whole processing stage of the fiber to usage of rotationally molded thermoplastic biocomposites. This involves finding a feasible cutting method, chemical treatments, weight percentages, blending techniques and composite testing. Flax fibers can be used as reinforcing filler over environmentally unfriendly glass fibers, can be modified to obtain desired mechanical properties and reduce the usage of petroleum-based plastics, (Burger et al. 1995). Flax fibers are currently being used in many diverse products. Automotive, building, and recreational industries are steadily increasing the usage of these fibers as a cost saving measure that is non-abrasive to processing machinery. Biocomposite products, besides being cost effective and environmentally friendly, are recyclable, have better acoustics and have good thermal insulation. When these biocomposites are rotationally molded many different shapes and colors can be achieved. The main impediment that is still to be overcome is that the farming and plastics industry do not currently have the infrastructure to build large quantities of composites materials. At the farming end, very few bulk handling and processing facilities currently exist for fibrous materials. These facilities should, once built, be located in rural areas where transportation costs are minimized, large scale cutting can occur and chemical treatments can be achieved. In other words it has the potential to be one of the few large value-added farming applications here in Saskatchewan and many agricultural centers. The plastics industry however can very easily start large-scale manufacturing of biocomposites. Blending of the materials and handling the fibers are the main areas of concern. Fortunately rotational molding machines do not need any adaptations for incorporating flax fibers into the process stream. Flax fibers are hygroscopic in nature, the fibers absorb or release moisture depending on the environmental conditions. Moisture absorption causes swelling of the
2
fibers that can lead to dimensional instability of the biocomposite, and reduction in some mechanical properties. Chemical treatments of the fiber can help stop this absorption process, (Panigrahi et al. 2002). Another problem associated with using flax fiber reinforcement is that the final product may have a distinct odor. Rotational Molding Process The rotational molding machine used for this work is located at Parkland Plastics in Saskatoon, Saskatchewan, Canada. It is a carousel-type molding machine that has four separate arms that can each rotate about two separate axes. By following the process of one of the four arms, it becomes easy to see how it is more of a four stage process that maximizes finished product quantity. The first arm is a loading arm where the mould cavities are filled, clamped and prepared. The arm at this stage is not being rotated. This arm then moves into the heating area where a galvanized steel shell houses the rotating arm. In this shell, the product is heated to 250°C until the material starts to melt and stick to the inner surface of the mold cavity. When the material has thoroughly melted and built a uniform layer over the inner mould cavity surface it is then moved into a cooling chamber while under constant rotation. If the arm stops rotating an this stage, the molten material will be affected by gravity and pool at the bottom of the cavity. The cooling chamber is the arms third stage and is where the material hardens into its final shape. Forced air is blown over the mould cavities to increase cooling rates. The fourth and final stage is the unloading stage where the finished product is further cooled with the mold lids off then removed. Figure 1 below shows how this process works.
Figure 1. Four stages of rotational molding 3
This particular machine at Parkland Plastics can be adjusted for many different applications. Single large mold cavities can be placed on each arm or many smaller shapes. The individual arms can also be adjusted for rotation, and heated at varying temperatures depending on the desired application. Table 1 below highlights some of the advantages and disadvantages of using a rotational molding machine. Table 1. Advantages and disadvantages of rotational molding
Advantages
Disadvantages
Molds are simple and inexpensive (low Labour intensive (loading and unloading) pressure) Molds of different size and shape can be Not suited to large production runs of small used on same equipment parts Good wall thickness uniformity Products can be almost stress free Material The plastic material being used in the preliminary testing is linear low-density and high-density polyethylene. The flax fiber is the linseed variety grown in Saskatchewan and decorticated on a standard scotching mill. The fiber was cut in 2 to 5 mm lengths before addition to the composite. So far, flax fiber is the only reinforcement material being tested, however hemp fibers are a potentially viable alternative. It is available in bulk quantities at very cheap prices near the research facility. Table 2 and 3 show how flax fiber compares to other fibers, both agricultural and man-made. Table 2 is the compositions of agricultural fibers and Table 3 is a comparison with man made E-glass fibers used extensively in the plastics industry. Table 2. Comparison of natural fiber compositions, (Panigrahi et al. 2002)
Fiber
Cellulose
HemiCellulose
Pectin/Lignin Wax
Flax Hemp Jute Sisal
64.1 67.0 64.4 65.8
13.7 16.1 12.0 12.0
3.8 4.1 12.0 10.7
1.5 0.7 0.5 0.3
4
Table 3. Glass fiber properties compared to flax fiber, (Panigrahi et al. 2002)
Properties
Flax
E-glass
Density (g/cm³) Tensile Strength (MPa) E-Modulus (GPa) Specific (E/density) Elongation at Failure (%) Moisture absorption (%)
1.5 800-1100 40-100 26-66 1.2-1.6 7
2.55 2400 73 29 3 -
Cutting A cutting machine is currently being developed at the Agricultural and Bioresource Engineering department at the University of Saskatchewan. The requirements for the machine when done will be to cut the high strength fibers into short 2 to 5 mm lengths, be able to process large quantities of fiber daily and to be as inexpensive as possible. The initial work is looking at using a rotating blade to cut the fibers against a shear bar. Some problems being encountered are keeping the cutting blades as close as possible to the shear bar in order to cut the material and not bend it. Another problem is a collection system that is capable of retaining the short fibers. If the machine is to be used inside this is a necessity. Chemical Treatments Preliminary work is also being conducted on how to chemically treat the fibers before being processed into the biocomposite. It is known that chemical treatments can decrease the water absorption of the fibers, clean the fiber surface, chemically modify the surface or increase the surface roughness in order to increase the interface adhesion between the fiber and the matrix, (Yuan et al. 2001). Some of the chemical treatments currently being used are the plasma treatment technique and immersion in a 5 % NaOH solution for 24 hours. However other methods are also available. This chemical treatment step can be seen as a necessary hindrance to the biocomposite process. Treatment facilities will have to be built that can treat large quantities of fiber. It makes economic sense to build these facilities along with the cutting facilities, hopefully where the fibers are grown to increase the economic potential for rural areas. However, depending on the treatment method used, these facilities will have to manage the wastes created from these processes. Some of the treatment methods use harmful chemicals that have to be handled in an environmentally safe fashion.
5
Blending Blending of the plastic and the fiber is a very important component in biocomposite processing. This is one of the main challenges in rotational molding. Initial testing was done by mixing the fiber and plastic powder with a simple drill and mixing attachment but the inner surface of the molded material can have a build up of fiber if this is the only mixing step. The bulk density of thermoplastics is in the 500 to 600 kg/m³ range, while uncompressed lignocellulosic material is in the 50 to 250 kg/m³ range. This can lead to a poor mix depending on the rotational speeds used and the melting temperatures applied. Further research will involve using a screw extruder to mix the materials and pelletizing them. This extruder will also be used to conduct testing on how the fibers can be aligned in the matrix. The strength of the biocomposite can vary greatly depending on how the fibers are orientated. Initial testing has been conducted using only random orientation of the fibers, (Panigrahi et al. 2002). Weight Percentage of Fiber The weight percentage of fiber in the composite can be altered to suit individual product needs. If more fiber is added the tensile strength of the composite increases, or if more friction is needed the fiber content can also be increased. An application for increased friction is in steps or stairs on home decks. The fiber content can also be decreased if the final product is to be used in extremely moist environments. This will help insure that shrinking and swelling of the product will be reduced. Figure 2 below shows the relationship of fiber weight percentage versus tensile strength. Tensile testing was conducting by cutting biocomposite samples into dumbbell shapes them pulling to the break point.
6
Fiber weight VS Tensile Strength 24 Tensile Strength, (MPa)
22 20 18 16
LDPE-Flax Fiber Composite
14 12 10 0
10
20
30
40
Fiber wt. %
Figure 2. Tensile strength of flax fiber-LDPE biocomposite Conclusion Flax fiber has a very promising future in the rotational molding industry. Plastic manufacturing is one of the few billion dollar industries, and flax fibers have the potential to break into this lucrative industry. The research we are conducting at the University of Saskatchewan will hopefully speed up or enhance the fibers potential. One of the main points of this research is that it is intended to help the flax growers and rural areas in particular. Saskatchewan farmers are currently undergoing a severe drought coupled with very low commodity prices. The flax fiber is already being produced and can be obtained relatively cheap compared to glass fiber reinforcements. Table 4 below highlights some of the advantages and problems of using flax fibers compared to glass fibers. Table 4. Advantages and problems with using flax fiber in biocomposites
Positives
Problems
Obtained Cheaply High strength Lightweight (Low Density) Environmentally Friendly Non-Abrasive to Machinery High Stiffness Good Acoustics
Absorbs Moisture Need Chemical Treatments Need Processing Infrastructure Odorous
7
References Burger, H., A. Koine, R. Maron, K-P. Meick.1995. Use of natural fibres and environmental aspects. International Polymer Science and Technology. 22: 25-34. Panigrahi, S., L. G. Tabil., W. J. Crerar, S. Sokansanj, J. Ward, T. Powell, A. J. Kovacs, L. Braun. Application of Saskatchewan grown flax fiber in rotational molding of polymer composites.2002. Presented at AIC 2002 Meeting SCAE/SCGR Program. Saskatoon, Sk, Canada. July 14-17, 2002. Morton, W. E. and J. W. S. Hearle.1993. Physical properties of textile fibres, 3rd edn. The Textile Institute. Felix, J. M., P. Gatenholm.1991. The nature of adhesion in composites of modified cellulose fibres and polypropylene. Journal of Applied Polymer Science. 42: 609-620. Yuan, Xiaowen., K. Jayaraman, D. Bhattacharyya.2001. Plasma treatment of sisal fibres and its effect on tensile strength and interfacial bonding. Presented at the Third International Symposium on Polymer Surface modification. Newark, New Jersey, USA. May, 2001. Sanadi, A. R., S. V. Prasad, P. K. Rohatgi.1985. Natural fibres and agro-wastes as fillers and reinforcements in polymer composites. Journal of Scientific and Industrial Research. 44: 437-442.
8
