- Email: [email protected]
Reinforcement of PP with flax
Additives,for Polymers
May 1998
variable speed stirrer, with a mixing vessel. As the components are added to the mixing vessel, the balance displays the weight, so avoiding errors caused by ‘weighing by difference’, or by overaddition of a particular component. At the beginning of each batch, the stirrer is set to a fixed speed between 50 and 1200 revolutions per minute. As the viscosity of the batch changes during processing, the torque on the stirrer varies, and this is detected and shown on a liquid crystal display. Contact: Sheen Instruments Ltd, I/nit 4, St
Georges Industrial Estate, Richmond Road, Kingston-upon-names, KT2 SBQ, UK; tel: -I-44-181541 4333;.fax: +44-181549 3374
NEW TECHNOLOGY Fine fibres for conductive plastics New technology has been developed for production of very fine metal fibres, which can be used in many applications, including as additives to render plastics electrically conductive. The process is described as ‘coil shaving’, and is faster and more versatile than traditional methods. Fibres of 20-100 pm diameter fibres can be produced from titanium, aluminium, nickel, copper and stainless steel, which offer improved conductivity in plastics compounds. Filter media, heat-resistant fabrics and motorcycle silencers are among other potential applications. The process was developed by Professor Yanagisawa, at the Nippon Institute of Technology (NIT), Saitama, Japan. It will be commercialized in a 60:40 joint venture by NV Bekaert SA, Belgium and Nippon Institute of Technology, under the name Bekinit KK. It derives from work which began in 1991 and a commercial product is knitted burner media, developed for Acotech, a joint venture between Bekaert and Shell.
0 1998 Elsevier Science
In the preliminary stages, development and production will be carried out at the NIT campus at Saitama, where trial production has already been started. The venture predicts that, when commercialized, sales of $1 billion (about USS8.3 million) will be achieved within four years. Contact: NV Behzert SA, Bekaert straat 2,
B-8550 Zwevegem, Belgium; tel: -C32-56 23051 I; fa: +32-56 230585
TECHNICAL
BRIEFS
Reinforcement of PP with flax Good fibre strength and rigidity, plus low price and environmental advantages encourage the use of vegetable bast and hard fibres such as flax, hemp, jute, ramie or sisal for reinforcement of thermoplastics. Production of large and low/medium stressed components in polypropylene reinforced with flax mat is gaining in popularity. With light but extremely rigid parts, flax fibre-reinforced plastics could compete with glass-reinforced materials for applications such as automobile interiors, but the possibilities of this material in highly stressed structural components depend of the properties of the composite under dynamic stress. However, there is virtually no information yet available on this. The normal test in dynamic evaluation of materials or components is the Wohler fatigue test, to characterize fatigue behaviour. Hysteresis measurements were carried out on flax and glass mat reinforced polypropylene, with a needle-punched flax mat using green and retted fibres to make plates with a quasi-isotropic composite structure, and with treatment by a coupling agent. Green and retted fibres differ in the degree of fibre digestion and physical data. Green flax fibres are stronger and much coarser (fineness >4 tex), but their modulus of elasticity is lower than that of retted fibres. Retted fibre has intensive fibre digestion, due to the action of moisture during retting,
7
May 1998
Additives for Polymers
Properties of flax reinforcement fibres Green flax
Fibre material retted flax
Glass
Density (g/cm”)
1.5
1.5
3.0
Fineness (tex)
4.7
2.7
0.3
Elongation at break (%)
2.6
2.1
3.6
Tensile strength (N/mm?
729
531
1817
Specific tensile strength (N/mm’ x cm”/g)
493
359
699
h;lodulus of elasticity (kN/mm2)
46.4
61.0
105.9
Specific modulus of elasticity (kN/mm’ x cm”/g)
31.4
41.2
40.7
Mean fibre length
47.1
36.7
50.0
Source: International
Polymer Science and Technology
producing fine fibres with a high modulus and low strength as a result of decomposiiion during retting. Green flax has less intensive fibre degradation due to only brief exposure to moisture, producing a coarser fibre bundle with high strength and low modulus due to good elongation at break. Unlike glass fibres, which have a round section, industrial flax fibres are made up of numerous individual fibres or fibrils bonded together by vegetable substances and have a rough surface, meaning that they can already be regarded as composite materials. Flax fibres have a lower strength and composites did not achieve the tensile strength values of glass mat reinforced polypropylene with the same fibre content. But high values were determined for modulus of elasticity. High quality green flax has a better reinforcing effect than retted flax: a content of some 40% by weight produces tensile stress values in the range of those for glass mat reinforced polypropylene at a content of 30%. Silane-treated fibres at 30% fibre content nearly reach the strengths and stifiesses of 40% flax/PP composites. The improvement in fibre matrix adhesion was found in both green flax and retted flax reinforced compounds. The investigation showed that polypropylene compounds reinforced with flax and glass mat, at comparable fibre contents, have!
8
similar fatigue strengths when exposed to dynamic repeated tensile stresses. The flax fibre composites are characterized by their high material damping, which is attributable to the specific properties of flax fibres. Tests at microscopic level found that it is usually microcracks, tending to run transverse to the stress direction, which are responsible for the failure of fibre composites. Increasing the fibre content and improving the fibre/matrix adhesion improves fatigue strength. International Polymer Science and Technoloa, Vol 23, No 9, 1996, pp T/14-T/20 (tr from Gummi E’asern Kunststoffe)
Reinforcing block ether-ester elastomers Block copolyether-ester elastomers (CPEE) fill a useful gap between the classical thermoplastics and elastomers. Their specific properties are related to their two-phase microstructure, built up of alternating flexible segments based on amorphous polyoxytetramethylene glycol and rigid crystalline segments based on poly(butylene terephthalate). They have good mechanical properties over a wide temperature range. Incorporation of fillers into CPEE, however, presents a problem, with the polymer in the continuous phase and the filler in a dispersed phase. Intermediate layers of 0.001 to 120 pm thick are formed between filler and
0 1998 Elsevier Science
May 1998
variable speed stirrer, with a mixing vessel. As the components are added to the mixing vessel, the balance displays the weight, so avoiding errors caused by ‘weighing by difference’, or by overaddition of a particular component. At the beginning of each batch, the stirrer is set to a fixed speed between 50 and 1200 revolutions per minute. As the viscosity of the batch changes during processing, the torque on the stirrer varies, and this is detected and shown on a liquid crystal display. Contact: Sheen Instruments Ltd, I/nit 4, St
Georges Industrial Estate, Richmond Road, Kingston-upon-names, KT2 SBQ, UK; tel: -I-44-181541 4333;.fax: +44-181549 3374
NEW TECHNOLOGY Fine fibres for conductive plastics New technology has been developed for production of very fine metal fibres, which can be used in many applications, including as additives to render plastics electrically conductive. The process is described as ‘coil shaving’, and is faster and more versatile than traditional methods. Fibres of 20-100 pm diameter fibres can be produced from titanium, aluminium, nickel, copper and stainless steel, which offer improved conductivity in plastics compounds. Filter media, heat-resistant fabrics and motorcycle silencers are among other potential applications. The process was developed by Professor Yanagisawa, at the Nippon Institute of Technology (NIT), Saitama, Japan. It will be commercialized in a 60:40 joint venture by NV Bekaert SA, Belgium and Nippon Institute of Technology, under the name Bekinit KK. It derives from work which began in 1991 and a commercial product is knitted burner media, developed for Acotech, a joint venture between Bekaert and Shell.
0 1998 Elsevier Science
In the preliminary stages, development and production will be carried out at the NIT campus at Saitama, where trial production has already been started. The venture predicts that, when commercialized, sales of $1 billion (about USS8.3 million) will be achieved within four years. Contact: NV Behzert SA, Bekaert straat 2,
B-8550 Zwevegem, Belgium; tel: -C32-56 23051 I; fa: +32-56 230585
TECHNICAL
BRIEFS
Reinforcement of PP with flax Good fibre strength and rigidity, plus low price and environmental advantages encourage the use of vegetable bast and hard fibres such as flax, hemp, jute, ramie or sisal for reinforcement of thermoplastics. Production of large and low/medium stressed components in polypropylene reinforced with flax mat is gaining in popularity. With light but extremely rigid parts, flax fibre-reinforced plastics could compete with glass-reinforced materials for applications such as automobile interiors, but the possibilities of this material in highly stressed structural components depend of the properties of the composite under dynamic stress. However, there is virtually no information yet available on this. The normal test in dynamic evaluation of materials or components is the Wohler fatigue test, to characterize fatigue behaviour. Hysteresis measurements were carried out on flax and glass mat reinforced polypropylene, with a needle-punched flax mat using green and retted fibres to make plates with a quasi-isotropic composite structure, and with treatment by a coupling agent. Green and retted fibres differ in the degree of fibre digestion and physical data. Green flax fibres are stronger and much coarser (fineness >4 tex), but their modulus of elasticity is lower than that of retted fibres. Retted fibre has intensive fibre digestion, due to the action of moisture during retting,
7
May 1998
Additives for Polymers
Properties of flax reinforcement fibres Green flax
Fibre material retted flax
Glass
Density (g/cm”)
1.5
1.5
3.0
Fineness (tex)
4.7
2.7
0.3
Elongation at break (%)
2.6
2.1
3.6
Tensile strength (N/mm?
729
531
1817
Specific tensile strength (N/mm’ x cm”/g)
493
359
699
h;lodulus of elasticity (kN/mm2)
46.4
61.0
105.9
Specific modulus of elasticity (kN/mm’ x cm”/g)
31.4
41.2
40.7
Mean fibre length
47.1
36.7
50.0
Source: International
Polymer Science and Technology
producing fine fibres with a high modulus and low strength as a result of decomposiiion during retting. Green flax has less intensive fibre degradation due to only brief exposure to moisture, producing a coarser fibre bundle with high strength and low modulus due to good elongation at break. Unlike glass fibres, which have a round section, industrial flax fibres are made up of numerous individual fibres or fibrils bonded together by vegetable substances and have a rough surface, meaning that they can already be regarded as composite materials. Flax fibres have a lower strength and composites did not achieve the tensile strength values of glass mat reinforced polypropylene with the same fibre content. But high values were determined for modulus of elasticity. High quality green flax has a better reinforcing effect than retted flax: a content of some 40% by weight produces tensile stress values in the range of those for glass mat reinforced polypropylene at a content of 30%. Silane-treated fibres at 30% fibre content nearly reach the strengths and stifiesses of 40% flax/PP composites. The improvement in fibre matrix adhesion was found in both green flax and retted flax reinforced compounds. The investigation showed that polypropylene compounds reinforced with flax and glass mat, at comparable fibre contents, have!
8
similar fatigue strengths when exposed to dynamic repeated tensile stresses. The flax fibre composites are characterized by their high material damping, which is attributable to the specific properties of flax fibres. Tests at microscopic level found that it is usually microcracks, tending to run transverse to the stress direction, which are responsible for the failure of fibre composites. Increasing the fibre content and improving the fibre/matrix adhesion improves fatigue strength. International Polymer Science and Technoloa, Vol 23, No 9, 1996, pp T/14-T/20 (tr from Gummi E’asern Kunststoffe)
Reinforcing block ether-ester elastomers Block copolyether-ester elastomers (CPEE) fill a useful gap between the classical thermoplastics and elastomers. Their specific properties are related to their two-phase microstructure, built up of alternating flexible segments based on amorphous polyoxytetramethylene glycol and rigid crystalline segments based on poly(butylene terephthalate). They have good mechanical properties over a wide temperature range. Incorporation of fillers into CPEE, however, presents a problem, with the polymer in the continuous phase and the filler in a dispersed phase. Intermediate layers of 0.001 to 120 pm thick are formed between filler and
0 1998 Elsevier Science