Eigenschaften von extrudierten Holz-Kunststoff-Werkstoffen auf Basis von Refiner-(TMP-)Fasern und Hanffasern

At present, wood particles (wood flour) with a low aspect ratio are mostly used as fillers in wood-plastic composites (WPC). Reinforcement of WPC and improved strength properties may be achieved by using real wood fibres with a high aspect ratio. WPC based on 70% (wt.) refiner (TMP) wood fibres and mechanically processed hemp fibres were extruded in a two-step process. Eleven compounds based on the two natural fibre types were prepared using a thermokinetic mixer and extruded in a conical, counter-rotating twin-screw extruder. Additional formulation components were polypropylene fibres, maleic anhydride-modified polypropylene (MAPP) and lubricant. It was determined that compounding in a thermokinetic mixer is a useful step for processing of WPC with refiner and hemp fibres as little fibre damage occurred. However, during extrusion, both natural fibre types were severely shortened due to strong shear forces, and homogeneous dispersion of fibres in the matrix was not achieved. WPC based on hemp fibres displayed the best strength properties of the formulations tested. Current extruder screw and die configurations need to be modified to achieve improved fibre reinforcement and to create new, structurally demanding applications for WPC. Using dynamic mechanical analysis, fibre-matrix adhesion of WPC was investigated, and activation energies for glass transition of selected formulations were calculated. Activation energy for formulations containing MAPP was higher than for WPC without MAPP. This indicates that better fibre-matrix adhesion was achieved in formulations with MAPP.     

Optimisation of the surface treatment of jute fibres for natural fibre reinforced polymer composites using Weibull analysis

Abstract

The natural bast fibres such as jute, flax, kenaf, hemp, ramie are chemically modified for improving the interfacial adhesion with the hydrophobic matrices. Alkali treatment is amongst the widely used chemical treatment for the surface modification of these natural fibres. In this study, jute fibres are treated with 0.5, 4 and 25?wt.% sodium hydroxide (NaOH) solution at room temperature for 24?hours, 30?min and 20?min respectively. A comparison has been made between the physical and mechanical properties of these untreated and alkali treated jute fibres. Subsequently, a comparison between the cross-sectional areas of jute fibres before and after alkali treatment by using SEM analysis and circular fibre assumption is also made. The aim of the work is to optimise the alkali treatment processes of jute fibres with different concentrations of NaOH at room temperature. Two-parameter Weibull distribution is also applied to analyse the tensile properties of untreated and different alkali treated jute fibres. It has been observed that probabilistic tensile strength is an effective technique rather than presenting the average tensile strength. The study clearly demonstrates the jute fibre treated with 0.5?wt.% NaOH is more feasible and effective way to improve the mechanical properties of natural fibre reinforced composites.     

Composites from Bast Fibres-Prospects and Potential in the Changing Market Environment

Abstract

Composite materials reinforced with natural fibres, such as flax, hemp, kenaf and jute, are gaining increasing importance in automotive, aerospace, packaging and other industrial applications due to their lighter weight, competitive specific strength and stiffness, improved energy recovery, carbon dioxide sequestration, ease and flexibility of manufacturing and environmental friendliness besides the benefit of the renewable resources of bast fibres. The market scenario for composite applications is changing due to the introduction of newer biodegradable polymers, such as PLA synthesized from corn, development of composite making techniques and new stringent environmental laws requiring improved recyclability or biodegradability for industrial applications where stress bearing capacities and micro-mechanical failures dictate serviceability. Bast fibre reinforced composites, made from biodegradable polymers, will have to compete with conventional composites in terms of their mechanical behaviour. Biocomposites, in which natural fibres, such as kenaf, jute, flax, hemp, sisal, corn stalk, bagasse or even grass are embedded in a biodegradable matrix, made as bioplastics from soybean, corn and sugar, have openedup new possibilities for applications in automotive and building products. Obviously, new approaches to research and development will be required to improve their mechanical properties, such as tensile, bending and impact resistance to match their performance and commercial competitiveness against petroleum based products. The research community has to look at the various possibilities of combining natural fibres, such as sisal, flax, hemp and jute with polymer matrices from non-renewable and renewable resources to develop cost effective biocomposites. This paper will review the newer products and techniques that can improve the properties of bast fibre based composites as well as potential structural and non-structural applications which can increase their market share.     

Effect of Chemical Treatment on Thermal,Mechanical and Degradation Behavior of Banana Fiber Reinforced Polymer Composites

ABSTRACT

The current research endeavor, explores the thermal, mechanical, and degradation behavior of alkaline treated banana fibers reinforced polypropylene composites. Composites incorporating BF (20% w: w) treated with NaOH (5% w: v) aqueous solution were developed using extrusion-injection molding processes. After chemical treatment, the tensile, flexural and impact strength of the composite increases by 3.8%, 5.17%, and 11.50%, respectively. Scanning electron microscope (SEM) observations of tested specimens confirm the fiber pull out and fiber fracture as the main reasons for failure of developed composites under tensile and impact loading. The specimens were exposed to two different environments, water immersion and soil burial for 5 weeks for the degradation studies. The degradation behavior of composites was measured in terms of variation in weight and mechanical properties (tensile, flexural, and impact). The maximum degradation in mechanical properties was observed for the composites buried under soil. The composite lost 7.69%, 12.06%, and 3.27% of tensile, flexural, and impact strength, respectively.     

Tribological properties of aramid–polypropylene composites from commingled yarns: influence of aramid fibre weight fraction

Commingling process involves the mixing of two types of filaments, viz. reinforcing and matrix-forming filaments in a nozzle with the help of compressed air leading to a homogenous distribution. During compression moulding, close placement of reinforcing and matrix-forming filaments reduces the mass transfer distance of the matrix and ensures proper wetting of fibres resulting in the enhanced properties of the composites. Three types of compression-moulded composites of polypropylene and Kevlar with different Kevlar fibre weight fractions were developed using commingled yarns. Studies on mechanical properties of these laminates confirmed that the composites having higher weight fraction of Kevlar fibre showed better tensile properties. Both abrasive and erosive wear rates showed a strong influence of Kevlar fibre weight fraction. With increase in weight fraction of Kevlar fibre, the erosion wear rate of the composites decreased as Kevlar fibres have higher wear resistance compared with polypropylene matrix. Similar trend was observed also in case of abrasive wear. The composites showed higher wear resistance while abrading the composite with polymer pin in a direction perpendicular to the fibre orientation as compared with abrading in a direction parallel to the fibre orientation.     

Enzymatic Modification of Hemp Fibres for Sustainable Production of High Quality Materials

SUMMARY

The main focus of this paper is the influence of processing parameters in enzymatic hemp separation on the fibre quality. The effect of NaOH-, EDTA- and Soda-pre-treatment, and enzymatic treatment with Lyvelin® was determined. The results show that processing parameters from, e.g., flax treatment can not easily be transferred to hemp, since there is a different pectin structure. NaOH treatment with low concentrations has only a very limited effect on fibre quality. In opposite to results known from flax, EDTA treatment has no effect on hemp separation. More successful is fibre pre-treatment by soda even in low concentrations. In addition the soda pre-treatment improves the efficiency of the subsequent enzymatic step.     

Methods of Determining the Fibre Content and Evaluating the Fibre Blending in Bicomponent Cellulose Blends

Abstract

Chemical methods of determining composition of blends with respect to blends of different fibres have been standardised in many countries. In Poland we also have numerous standards covering most blend types present in the produced textiles. However, these methods cannot be used for studies of quantitative composition of blends containing cotton and bast fibres. There are also methods, less popular and not standardised so far, of determining composition of blends on the basis of changes of the physical properties of the blend in relation to changes of the physical properties of its component fibres. Such methods are usually applied in research work. It seems, however, that they are worth popularising in quality control of half-products and final textiles, as well as in interoperational control.

Blending of fibres is one of the most important operations in yarn production processes. Irregularity of fibre blending has an adverse influence on the quality of yarns. Therefore, it is very important to study fibre blending at various stages of the spinning process and to select proper methods of studying the blending.

In this work we present and analyse methods used for determination of content and evaluation of blending of fibres in bicomponent cellulose blends.     

Processing of waste carbon and polyamide fibres for high-performance thermoplastic composites: influence of carding parameters on fibre orientation,fibre length and sliver cohesion force

Abstract

The processing of waste carbon fibre on carding machine for the developments of nonwovens, tapes and hybrid yarn structures is an emerging trend. These structures are widely used to enhance the performance efficiency of recycled carbon fibre reinforced thermoplastic composites. The aim of the research presented in this study is to process waste carbon fibre on a carding machine and to investigate the influence of different carding parameters on waste carbon fibre. For this purpose, card slivers composed of waste carbon and polyamide fibres were developed on a double cylinder card machine by varying technical parameters. Then, effect of these parameters on card sliver quality was assessed in terms of fibre orientation, fibre length and sliver cohesion force. Results revealed that fibre orientation and fibre length is significantly affected by technological parameters carding zones, whereas the sliver cohesion force is significantly affected by the speed of feed roller and doffer.     

Influences of moisture absorption and chemical treatments on the resin flow characteristics of natural fibre nonwoven mats

A major challenge for the use of natural fibres in polymeric composites is their incompatibility with commonly used matrices, causing weak interfaces of the final composites. Many surface treatments to natural fibres have been proposed to eliminate or reduce these problems. In this paper, we evaluate the influences of three commonly used natural fibre chemical treatments on the resin flow characteristics of flax fibre nonwoven mats in a vacuum-assisted resin transfer moulding process. The alkalization treatment significantly increases the in-plane permeability and flow anisotropy of the natural nonwoven mat due to changes in fibre diameter, fibre surface tension and mat structure. The effects of silane and acetylation treatments on resin flow are much smaller. It is well known that in comparison with glass fibre, natural fibres can absorb a large amount of moisture from surrounding air. The absorption of moisture causes a considerable reduction in the in-plane permeability of natural fibre nonwoven mats.     

A Review on Natural Fibre-Based Composites-Part I

Abstract

Natural fibre-based composites have been intensely studied in the last years due to their specific properties and their clearly positive environmental impact. Other advantages of using vegetable fibres are related to their economical production and processing, their safe handling and working conditions. Therefore, lignocellulosic natural fibres constitute an interesting alternative to traditional synthetic fibres in composite materials. This work is intended to present an overview of the main results presented in literature on this topic, focusing the attention on the fibres properties in terms of physical and chemical structure, thermal and mechanical properties. Some aspects related to the production of vegetable fibres for composites are also presented.     

Evaluation of physico-mechanical characteristics of cashew nut shell liquid-epoxy composites with Borassus and Tamarind fruit fibres as reinforcements

In this study, Cashew Nut Shell Liquid (CNSL)-epoxy matrix-based composites reinforced with borassus and tamarind fibres were fabricated using compression moulding technique. Three different types of composites were fabricated, namely Borassus fruit fine fibre/CNSL-epoxy composites (BF composites), Tamarind fibre/CNSL-epoxy composites (TF composites) and Tamarind/Borassus fruit fine fibre CNSL-epoxy hybrid composites (HB composites). In addition, CNSL-epoxy neat polymer was also fabricated for comparison. Physical properties such as micro-hardness, void percentage, and mechanical properties like tensile, flexural, Interlaminar Shear Strength (ILSS), and impact strength were investigated. Scanning Electron Microscope (SEM) was used to study the failure mechanism of the composites. Experimental results indicate that tensile and flexural properties of BF composites were higher when compared to TF and HB composites. Micro-hardness and impact strength of HB composites were better than the others. SEM images indicated better fibre-matrix bonding in BF composites indicating improved resistance to delamination. Thus, borassus and tamarind fibre reinforced CNSL-epoxy composites can be used as an alternative material for light to moderately loaded structural engineering applications.     

Evaluation of the Influence of Fibre Length and Concentration on Mechanical Performance of Hemp Fibre Reinforced Polypropylene Composite

Abstract

The paper deals widi die evaluation of interfacial shear stress (ISS) between reinforcement fibre (hemp) and polypropylene matrix through single fibre pull-out method and subsequently the critical length of the composite grade hemp fibre has been determined. In the present study the average ISS value of 5.9 MPa was used to determine the critical length of hemp fibre, which was found to be 3.4 mm. The theoretical prediction of the tensilestrength and modulus of hemp-polypropylene composite by using Kelly-Tyson and Cox-Krenchel models, respectively, have been reported in the paper. Model results were validated by experimental works with different fibre lengths and volume fraction of hemp fibre in the composite. The effect of fibre length and content on the flexural strength and stiffness of the hemp-polypropylene composite has also been studied. The effect of moisture absorption on composite tensile strength was predicted by modifying the Kelly-Tyson model. The model curve was also compared with another set of experimental works done at differentmoisture contents in the composite.     

Sustainability and Profitability Through Intelligent Value Chain Management in Bast Fibre Processing

Abstract

The excellent properties of natural fibres like flax and hemp have not yet been fully exploited for high added value applications such as use in bio-based natural textiles and high performance fibres. There are few practical applications, although today's know-how in fibre purification, modification and application allow for a large array of viable bio-based products. Currently the development of these natural fibres is strongly determined by the EU subsidy regulations, which drive the motivation of farmers and processors. Due to the expansion of the European Union, agricultural subsidies will decrease in the next decade. Natural fibres will compete only successfully against these reductions by fulfilling three key factors:

? Product quality: The continuing lack of pure, fine and homogenous fibres has to be overcome.

? Market demand: Market demand is driven by product quality. There is a big and increasing demand for high quality upgraded natural fibres in textile and non-textile industry.

? Price: Farmers and fibre producers must have a reasonable economic basis.

Today the economic situation in the agricultural sector is extremely poor without subsidies. However, with each subsequent processing step in the fibre production value chain (mechanical refining, fibre upgrading by wet refining) the profitability increases significantly. To gain economic sustainability in the whole value chain (including spinning and weaving) the more profitable, high added value processing steps at the end of the chain should be employed to offset the less profitable steps. To realise this, we recommend a contract-network between agriculture, mechanical refining, upgrading and manufacturing of half-finished products. The business, which upgrades fibres, owns the innovative key-processing step (quality drives demand). It will lead the network and market fabrics with higher value and better profit by itself. All partners in the network participate by receiving fair prices. This will also guarantee continuous production of high quality raw material by farmers. A detailed operational calculation of the network shows promising results with a good internal rate of return.     

Monitoring the Diameter Changes of Flax Fibre Elements during Twin Screw Extrusion Using X-Ray Computed Micro-Tomography

ABSTRACT

Fiber size aspect ratio is known to impact the mechanical and reinforcement properties of natural fiber-based composites. However, the representation of fiber diameter change occurring during the extrusion process is controversial compared to the length. Fiber elements undergo multidirectional stresses and complex interactions within the extruder, leading to their breakage, which consequently may modulate their reinforcing properties. To better understand these mechanisms, short fiber reinforced polymer composites were prepared from flax fibers and polypropylene matrix (PP) by melt mixing. Five sampling zones were selected along the screws, both in screw conveying elements and inside blocks of kneading discs. X-ray computed micro-tomography, and 3D images analysis were then used for monitoring sample diameter distributions along the screw profile, according to specific twin-screw compounding conditions. The effects of the considered processing condition on fiber bundle diameters decrease along the screw profile are quantified.     

Advanced Decortication Technology for Unretted Bast Fibres

Abstract

Advanced decortication technology is based on a simple mechanical process, in which bast fibres are decorticated by impact stress. Hemp, flax and linseed are processed with the same technology that is suitable for both unretted and retted plants. The process includes all stages from the reception of the straw bales to the separate final products, which are fibres and shives.

The industrial requirements of technical fibres regarding fibre yield, fibre length, fineness and cleanness, are met.

The possibility of processing unretted bast fibres without any negative influence on the fibre qualities is advantageous. Harvesting of unretted fibre plants saves expenditure on the field and reduces the weather risk.     

Mechanical properties of natural fibre-reinforced composites

Natural fibres were initially used in composite materials to predominately improve bulk and reduce cost rather than improving mechanical properties. But the environmental problems associated with the production and use of synthetic fibres have changed the scenario. In the previous decade, natural fibres have been extensively used as reinforcement materials for both synthetic and bio-degradable matrices. Natural fibre reinforcements have mostly improved flexural and impact properties, but tensile strength improvement has been marginal and has been an area of investigation. Many attempts have been made towards improving mechanical properties, with efforts directed at improving the interface, newer methods of production of composites, new modelling techniques etc. In this detailed review, an attempt is made to critically analyse the various research efforts directed towards improving the mechanical properties of natural fibre reinforced composites.     

Characterization and Determination of Properties of Sri Lankan Coconut Fibres

Abstract

Coir fibre native to Sri Lanka was characterized morphologically, physically and chemically. The structure was studied using scanning electron and optical microscopy. The surface structure of the fibres develop with soaking time due to the removal of pith cells adhering to the fibre surface. Surface of the fibre display many pinhole like structures which are known as pits, the sizes of the pits vary with the fibre type. The structure of fibres is quite simple in cross sections with a vascular region surrounded by a sheath of sclerenchymetous cell layers. When fibres become mature deterioration of the cells in the vascular region cause the central cavity. Fibres consist of longitudinally oriented little fibrils, which are interconnected together by intercellular substances. Physical properties such as breaking load, elongation, and tensile strength were evaluated for fibres from five different varieties of coconuts. The results showed there is a variation among fibres obtained from different coconut varieties. Chemical analysis showed that fibres mainly consist of holocellulose and lignin.     

Toughness Characteristics of Arenga pinnata Fibre Concrete

Abstract

This paper reports the results of an investigation on the toughness characteristics of concrete containing Arenga pinnata fibre. Three fibre lengths of 15 mm, 25 mm, and 35 mm were used in two volume fractions, i.e., 0.6% and 0.8%. The values of toughness, first crack deflection, first crack toughness, toughness indices, and residual strength factors are presented for ages up to 180 days. It was observed that the addition of Arenga pinnata fibre increased the toughness characteristic of concrete. However, it was observed that the positive effects of the fibre become less significant after 28 days, but still sufficient to give the concrete better toughness properties compared to the plain concrete.This is due to reaction of the fibres with the alkaline pore water in the cement matrix.