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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.7, #5-6)
A Unified Nomenclature for Plant Fibres for Industrial Use by Julian F. V. Vincent (pp. 269-271).
Cellulose in the cell wall occurs in microfibrils of various sizes. “Fibre” should refer only to single elongated plant cells, “fibre bundle” to assemblages of fibres. Fibres and bundles can be of various cell types (most sclerenchyma), sizes, volume fractions of cellulose and degree of lignification. Usage of any other terms is liable to lead to confusion. Fibre bundles for industrial use should be defined only by their dimensions, botanical origin and the extraction procedures used.
Keywords: microfibril; fibre; fibre bundle; sclerenchyma; lignin; nomenclature; cell wall; cellulose
Environmental Durability of Flax Fibres and their Composites based on Polypropylene Matrix by A. Stamboulis; C. A. Baillie; S. K. Garkhail; H. G. H. van Melick; T. Peijs (pp. 273-294).
The environmental degradation behaviour of flax fibres and their polymer composites are explored. New upgraded Duralin flax fibres, which have been treated by a novel treatment process for improved moisture and rot sensitivity were studied. Environmental studies showed that these upgraded Duralin flax fibres absorb less moisture than untreated Green flax fibres, whereas the mechanical properties of the treated fibres were retained, if not improved. The effect of this novel flax fibre treatment on the environmental behaviour of natural-fibre-mat-reinforced thermoplastics (NMTs) is investigated by monitoring the moisture absorption and swelling, and measuring the residual mechanical properties of the flax/polypropylene composites at different moisture levels. The moisture absorption and swelling of the upgraded flax fibre composites is approximately 30% lower than that of composites based on Green flax fibres.
Keywords: natural fibres; flax fibres; Duralin; polypropylene; thermoplastic composites; NMT; moisture absorption; environmental properties
Oil Palm Fibre Reinforced Phenol Formaldehyde Composites: Influence of Fibre Surface Modifications on the Mechanical Performance by M. S. Sreekala; M. G. Kumaran; Seena Joseph; Maya Jacob; Sabu Thomas (pp. 295-329).
Oil palm fibres have been used as reinforcement in phenol formaldehyde resin. In order to improve the interfacial properties, the fibres were subjected to different chemical modifications such as mercerisation, acrylonitrile grafting, acrylation, latex coating, permanganate treatment, acetylation, and peroxide treatment. The effect of fibre coating on the interface properties has also been investigated. Morphological and structural changes of the fibres were investigated using scanning electron microscopy and IR spectroscopy. Mechanical properties of untreated and treated fibres were studied. Changes in stress–strain characteristics, tensile strength, tensile modulus and elongation at break of the fibres upon various modifications were studied and compared. The incorporation of the modified fibres resulted in composites having excellent impact resistance. Fibre coating enhanced the impact strength of untreated composite by a factor of four. Tensile and flexural performance of the composites were also investigated. Finally, inorder to have an insight into the failure behaviour, the tensile and impact fracture surfaces of the composites were analysed using scanning electron microscope.
Keywords: composites; oil palm fibre; phenol formaldehyde; chemical modifications; interface properties
The Effect of Alkali Treatment on the Adhesion Characteristics of Sisal Fibres by E. T. N. Bisanda (pp. 331-339).
The effect of alkali treatment on the wetting ability and coherence of sisal-epoxy composites has been examined. Treatment of sisal fibre in a 0.5N solution of sodium hydroxide, resulted into more rigid composites with lower porosity and hence higher density. The treatment has been shown to improve the adhesion characteristics, due to improved work of adhesion because it increases the surface tension and surface roughness. The resulting composites showed improvements in the compressive strength and water resistance. It has been suggested that the removal of intracrystalline and intercrystalline lignin and other surface waxy substances by the alkali substantially increases the possibility for mechanical interlocking and chemical bonding. The alkali treatment is simple and is recommended to precede other sophisticated surface modification treatments on plant fibres similar to sisal fibre.
Keywords: cellulose; mercerization; sisal; epoxy; water absorption; adhesion
RTM Hemp Fibre-Reinforced Polyester Composites by Gilles Sèbe; Nihat S. Cetin; Callum A. S. Hill; Mark Hughes (pp. 341-349).
Hemp fibre-reinforced polyester composites were prepared using a Resin Transfer Moulding (RTM) technique and the flexural and impact behaviour investigated. Flexural stress at break and flexural modulus showed an increasing trend with fibre content. Impact strength was found to decrease at low fibre content, then gradually increase with further addition of fibres.A strong interfacial adhesion between hemp and polyester was obtained using chemically modified hemp. This modification consisted in introducing reactive vinylic groups at the surface of the fibres, via esterification of hemp hydroxyl groups, using methacrylic anhydride. Increased bonding between fibres and matrix did not affect the flexural stress at break of the composite but was detrimental to toughness. This behaviour was ascribed to a change in the mode of failure, from fibre pull-out to fibre fracture, resulting in a marked reduction in the energy involved in the failure of the composite, leading to a more brittle material.
Keywords: plant fibres; hemp; reinforced composites; polyester; RTM; flexural stress; impact strength; interfacial bonding; esterification; microcompressive defects
Mechanical Properties of Natural-Fibre-Mat- Reinforced Thermoplastics based on Flax Fibres and Polypropylene by S. K. Garkhail; R. W. H. Heijenrath; T. Peijs (pp. 351-372).
Thermoplastic composites based on flax fibres and a polypropylene (PP) matrix were manufactured using (i) a film-stacking method based on random fibre mats and (ii) a paper making process based on chopped fibres. The influence of fibre length and fibre content on stiffness, strength and impact strength of these so-called natural-fibre-mat-reinforced thermoplastics (NMTs) is reported and compared with data for glass-mat-reinforced thermoplastics (GMTs), including the influence of the use of maleic-anhydride grafted PP for improved interfacial adhesion. In addition some preliminary data on the influence of fibre diameter on composite stiffness and strength is reported. The data is compared with the existing micro-mechanical models for strength and stiffness. A good agreement was found between theory and experiment in case of stiffness whereas in the case of strength the experimental values fall well below the theoretical predictions. Results indicated that NMTs are of interest for low-cost engineering applications and can compete with commercial GMTs when a high stiffness per unit weight is desirable. Results also indicated that future research towards significant improvements in tensile and impact strength of these types of composites should focus on the optimisation of fibre strength rather than interfacial bond strength.
Keywords: thermoplastic composites; NMT; GMT; natural fibre; flax fibre; polypropylene; adhesion; mechanical properties
Possibilities to Improve the Properties of Natural Fiber Reinforced Plastics by Fiber Modification – Jute Polypropylene Composites – by J. Gassan; A. K. Bledzki (pp. 373-385).
The influence of the fiber-matrix adhesion in jute fiber-reinforced polypropylene on the materials behavior under fatigue and impact loadings was investigated throughout this study. It was shown that a strong interface is connected with a higher dynamic modulus and reduction in stiffness degradation with increasing load cycles and applied maximum stresses. The specific damping capacity resulted in higher values for the composites with poor bonded fibers. Furthermore, the stronger fiber-matrix adhesion reduced the loss-energy by non-penetration impact tested composites with roughly 30%. Tests which were performed at different temperatures, showed higher loss energies for cold and warm test conditions compared with room temperature. Post-impact dynamic modulus after 5 impact events was roughly 40% and 30% lower for composites with poor and good fiber-matrix adhesion, respectively.
Keywords: jute-polypropylene composites; film stacking; interface; interphase; grafted polypropylene; fatigue behavior; impact behavior; post-impact behavior
Influence of the Physical Structure of Flax Fibres on the Mechanical Properties of Flax Fibre Reinforced Polypropylene Composites by M. J. A. van den Oever; H. L. Bos; M. J. J. M. van Kemenade (pp. 387-402).
This study investigates the influence of the physical structure of flax fibres on the mechanical properties of polypropylene (PP) composites. Due to their composite-like structure, flax fibres have relatively weak lateral bonds which are in particular present in flax fibres that are often used in natural fibre mat reinforced thermoplastics (NMT). These weak bonds can be partly removed by combing the fibres. In order to study the influence of the physical structure of flax fibres on NMT tensile and flexural properties, uncombed and combed flax fibre reinforced PP composites were manufactured via a wet laid process. The influence of improved fibre-matrix adhesion was studied using maleic-anhydride grafted PP. Results indicated that the flax physical structure has a significant effect on flax-PP composite properties and that the flax fibre reinforced PP properties are similar to values predicted with existing micromechanical models. The tensile modulus of flax-PP composites can fairly compete with commercial glass mat reinforced thermoplastic (GMT) modulus, the strength, however, both tensile and flexural, can not. In order to rise the strength of flax fibre reinforced PP composites to the level of GMT strength, the flax fibres have to be further isolated to elementary flax fibres.
Keywords: agrofibre physical structure; thermoplastic composites; tensile and flexural properties; improved adhesion
Mechanical Properties of Natural Fibre Mat Reinforced Thermoplastic by Kristiina Oksman (pp. 403-414).
The use of natural fibres instead of man made fibres, as reinforcements in thermoplastics, gives interesting alternatives for production of low cost and ecologically friendly composites. In this work different commercially available semi-finished natural fibre mat reinforced thermoplastics (NMT) composites have been studied. Mechanical properties and microstructure of different NMT composites were investigated and compared to conventional GMT (glass fibre mat reinforced thermoplastic) composites and pure polypropylene (PP). The study included also NMT composites manufacturing processing parameters as processing temperatures and pressure during compression moulding. The results showed that NMT composites have a high stiffness compared to pure polymer and the NMT with a high fibre content (50% by weight) showed even better stiffness than the GMT. The GMT composites had superior strength and impact properties compared to the NMT which might be due to the relatively low strength of the natural fibres but also to poor adhesion to the PP matrix. The NMT materials showed a large dependence on direction and are therefore believed to have more fibres oriented in one direction. The stronger direction (0°) of the NMT was in some cases as much as 45% better than the 90° direction.
Keywords: flax fibres; natural fibres; thermoplastics; tensile properties; impact properties; anisotropy; electron microscopy; morphology; compression moulding; processing
Natural Fibre Mat Thermoplastic Products from a Processor's Point of View by J. C. M. de Bruijn (pp. 415-420).
Natural fibres have significant advantages over glass, as an alternative fibre reinforcement material. Natural fibres are more environmentally friendly, healthier and safer, and cause less abrasive wear of processing equipment. On the other hand, their mechanical properties show a large scatter, and are at best equivalent to glass (natural fibres, however, have a lower density). Further disadvantages of the current natural fibre reinforced materials are their moisture sensitivity – which makes them prone to swelling and rotting – their smell and their current cost level.Experiments with the application of Natural Fibre Mat Thermoplastics (NMT) on current automotive products proved the disadvantages. On the other hand it yielded several new research themes concerning property limits and gave insight in the area's where to optimize in order to get a broad application of natural fibre reinforced plastic products.Looking towards the long term, other alternatives, like bio-composites or all-PP composites should be further explored.
Keywords: composites; automotive; natural fibres; processing
Composites from Natural Fibers and Soy Oil Resins by George I. Williams; Richard P. Wool (pp. 421-432).
The goal of this project is to develop new composites using fibers and resins from renewable resources. The ACRES (Affordable Composites from Renewable Sources) group at the University of Delaware has developed new chemistries to synthesize rigid polymers from plant oils. The resins produced contain at least 50% plant triglycerides and have mechanical properties comparable to commercially available synthetic resins such as vinyl esters, polyesters and epoxies. This project explores the development of all-natural composites by using natural fibers such as hemp and flax as reinforcements in the ACRES resins. Replacing synthetic fibers with natural fibers has both environmental and economic advantages. Unlike carbon and glass fibers, natural fibers are abundantly available from renewable resources. In terms of cost, natural fibers are cheaper than the synthetic alternatives. The natural fibers and plant-based resins have been shown to combine to produce a low cost composite with good mechanical properties. Tensile strength in the 30 MPa range has been obtained for a composite containing about 30 wt% Durafibre Grade 2 flax. The tensile modulus was found to be 4.7 GPa for a 40 wt% flax composite. Similar numbers where obtained for the hemp composites obtained from Hemcore Inc. Composites from renewable resources offer significant potential for new high volume, low cost applications.
Keywords: composites; natural fibers; soy oil; synthesis; manufacturing; mechanical properties; resins
Lignocellulosic Fibre Reinforced Caseinate Plastics by M. Fossen; I. Ormel; G. E. T. van Vilsteren; Tj. Jongsma (pp. 433-437).
Caseinate plastics were reinforced with two lignocellulosic fibres, i.e. wood pulp fibre and flax bast fibre by means of kneading and subsequent injection moulding. The tensile modulus increased from 200 MPa for the unfilled plastic to 1200 MPa at 20 wt% fibre addition. Simultaneously, the tensile strength increased from 6 to 30 MPa going from 0 to 20 wt% fibre incorporation. These results indicate a good interaction between the fibres and the mainly hydrophilic caseinate matrix.
Keywords: caseinate; protein; fibre; mechanical properties; SEM