Natural Fibre-reinforced Thermoplastic Composites Research Articles

Optimization of process parameters during flax and polypropylene composite manufacturing using Box-Behnken design of experiments

Composites produced from recyclable polymers are of greater scope in the industrial sector owing to their better quality, sustainability, and environmental considerations. In this study, flax fibre utilized as reinforcement and polypropylene fibre used as a matrix were used for producing thermoplastic composites. Flax/polypropylene needle punched non-woven was performed by a compression moulding process. Process parameters, temperature, time, and pressure were selected to optimize the flax/polypropylene (PP) production process using Box- Behnken Experimental Design (BBD) and response surface methodology. The effects of the process parameters on the material's tensile, flexural, and short beam shear strengths were studied. Furthermore, the research parameters were used to analyze of variance (ANOVA) and regression models for estimating the mechanical properties. Also, Scanning Electron Microscope (SEM) analyses were performed on the composites to study the surface morphologies in composites. The findings revealed that temperature was the ultimate cause influencing the mechanical properties, followed by pressure and time. Surface morphologies confirm the better bonding between the flax fibres and PP matrix. This work shall effectively choose the ideal values of process parameters for producing natural fibre-reinforced thermoplastic composites.

Effects of Water and Chemical Solutions Ageing on the Physical, Mechanical, Thermal and Flammability Properties of Natural Fibre-Reinforced Thermoplastic Composites.

Biocomposites comprising a combination of natural fibres and bio-based polymers are good alternatives to those produced from synthetic components in terms of sustainability and environmental issues. However, it is well known that water or aqueous chemical solutions affect natural polymers/fibres more than the respective synthetic components. In this study the effects of water, salt water, acidic and alkali solutions ageing on water uptake, mechanical properties and flammability of natural fibre-reinforced polypropylene (PP) and poly(lactic acid) (PLA) composites were compared. Jute, sisal and wool fibre- reinforced PP and PLA composites were prepared using a novel, patented nonwoven technology followed by the hot press method. The prepared composites were aged in water and chemical solutions for up to 3 week periods. Water absorption, flexural properties and the thermal and flammability performances of the composites were investigated before and after ageing each process. The effect of post-ageing drying on the retention of mechanical and flammability properties has also been studied. A linear relationship between irreversible flexural modulus reduction and water adsorption/desorption was observed. The aqueous chemical solutions caused further but minor effects in terms of moisture sorption and flexural modulus changes. PLA composites were affected more than the respective PP composites, because of their hydrolytic sensitivity. From thermal analytical results, these changes in PP composites could be attributed to ageing effects on fibres, whereas in PLA composite changes related to both those of fibres present and of the polymer. Ageing however, had no adverse effect on the flammability of the composites.

A Review of the Impact Performance of Natural Fiber Thermoplastic Composites

Many academic studies continue to conclude that natural fibre reinforced thermoplastic composites (NFTCs) have some potential to compete with mineral/inorganic fibre and filler reinforced composites in certain applications due to their distinctive characteristics. NFTCs are often presented as a more environmentally friendly product which may, in some cases, offer useful levels of specific strength and stiffness with an overall reduced carbon footprint. However, from an end-use composite performance viewpoint, issues with impact resistance (notched and un-notched) continue to hold back the large-scale implementation of these composites. This paper presents a review of the recent work on impact properties of NFTCs, analysing the effects of fundamental composite parameters and potential routes to improvement.

Natural fibre-reinforced thermoplastic composites from woven-nonwoven textile preforms: Mechanical and fire performance study

Partially and fully biodegradable natural fibre – reinforced composites have been prepared using a novel patented woven-nonwoven technology. Natural fibres included jute and sisal, whereas the matrices were of synthetic polymers derived from petroleum (polypropylene (PP)) or natural (polylactic acid (PLA)) resources. The physical, mechanical and flammability properties of these partially and fully biodegradable composites have been studied and compared with those of similarly produced glass-fibre reinforced PP and PLA composites with a view to enabling their use in automotive applications. Mechanical test results showed that the tensile and flexural moduli of the PLA composites were higher than respective PP composites. In comparison, sisal composites have higher tensile and flexural moduli than jute composites. The fire performance of the composites studied by cone calorimetry showed that while natural fibre reinforcement had no effect on time-to-ignition, peak heat release was significantly reduced. PLA composites had lower burning propensity compared to respective PP composites.

Sheet forming of flax reinforced polypropylene composites using vacuum assisted oven consolidation (VAOC)

Fibre reinforced plastics are widely used in different industry sectors since the past half century. Considerable research has been carried out on natural fibres as reinforcements because of their light weight, good mechanical properties, biodegradability, sustainability and higher stiffness per unit mass compared to glass fibres. This paper develops a knowledge base for the manufacture of vacuum assisted fibre reinforced thermoplastic composites inside a simple oven from sheets of the fibre and the thermoplastic. The compaction behaviour of the reinforcements used was investigated and used to target a range of achievable fibre volume fractions to manufacture the composites. The reinforcements were also characterized on the basis of their transverse permeability to quantify the ease of polymer flow through the reinforcements. An experimental setup was designed to measure the relevant processing parameters during the experiment. Thickness, pressure and temperature of the composites were monitored with applied vacuum pressure and oven temperature during the experiments. The mould temperature inside the oven was first increased to the melting temperature of the thermoplastic, held at that temperature for a certain time period and then cooled subsequently. The application of compaction pressure and the holding time was varied to study its effect on consolidation quality. The achieved fibre volume fraction of the manufactured composites was calculated by first using the average thickness of the composites and then using the density of the composite. The cross-section of the laminates was examined under an optimal microscope to evaluate the quality of consolidation. Tensile and short beam shear tests were performed to assess structural integrity, strength and stiffness of the composites. The results show that this manufacturing technique can produce composites at expected fibre volume fractions under vacuum. The cooling rate, applied temperature, pressure and sheet layup were found to have considerable effects on the fibre volume fraction. It was also found that the mechanical properties of natural fibre reinforced thermoplastic composites (NFRTS) do not change appreciably even after modifying the process so as to reduce the manufacturing time.

Curing of natural fibre-reinforced thermoplastic composites using microwave energy

Natural fibre-reinforced polymer composites are seen as a possible substitute to synthetic fibre-based composites to face the environmental issues related to non-biodegradable nature of synthetic fibres. Due to their high specific strength and modulus, natural fibre-reinforced polymer composites are receiving widespread attention. In the present research initiative, natural fibre-reinforced thermoplastic composites have been developed with microwave curing technique. Two types of natural fibres namely sisal and grewia optiva, and two types of thermoplastic polymers (polypropylene and ethylene vinyl acetate) were used for fabrication of composites. Microwave wattage and exposure time were optimized for successful curing of thermoplastic composites. Results of tensile, flexural and impact strength of developed composites showed improvement in the properties as compared to neat polymers. The results suggest that microwave energy provides a feasible, environmental friendly option for curing of natural fibre-based thermoplastic composites.

Effect of fibre loading on mechanical and thermal properties of sisal and kenaf fibre-reinforced injection moulded composites

Kenaf and sisal fibres were selected for the development of natural fibre-reinforced thermoplastic composites because they are in abundance in South Africa. These materials can be used in the building industry, where good mechanical and fire resistance properties are required for structural and non-structural applications. High load bearing, moisture and fire can negatively affect the properties of these composites and decrease their performance. The effect of water glass, maleic anhydride-grafted-polypropylene (MAPP) treatment and fibre loadings on mechanical and thermal properties as well as fire resistance of kenaf and sisal fibre-reinforced polypropylene composites were investigated. The fibre-reinforced polypropylene composites were produced by injection and compression moulding processes. A significant improvement of the tensile strength and modulus of kenaf fibre composites was more pronounced when compared to sisal fibre composites. However, the water glass has a slight negative influence on mechanical properties of fibre/polypropylene matrix composites but showed better fire resistance and thermal properties when compared to the untreated fibre/polypropylene composites. Generally, the impact strength of fibre/polypropylene composites decreased with the addition of MAPP. The low impact strength could be the results of weak interfacial bond strength between the fibre and the matrix. The total heat release was reduced by water glass treatment due to the non-flammable polysilicate coating, while the average mass loss rate was slightly reduced by MAPP.

Solvent Uptake and Accelerated Solar Aging Studies of Cotton – Polypropylene Commingled Composite Systems

Natural fibre-reinforced thermoplastic composites have a significant role in non-structural applications. Natural fibres are biodegradable, renewable and of low cost, high toughness and possess good thermal properties. This work involved the study of solvent absorption of cotton/polypropylene (PP) side-by-side commingled composites in different solvents, its variation by chemical treatments, temperature, fibre content etc., the extent of tensile property deterioration by solar radiation in a solar light concentrator and by water diffusion. It was observed that though cotton is highly hydrophilic, the diffusion was a matrix-dominated phenomenon. The extent of moisture absorption increased with the fibre content but decreased on treatment with maleic anhydride-modified PP. The former added a greater number of hydrophilic hydroxyl groups while the latter consumed them and enhanced the fibre–matrix interfacial adhesion. Increase in temperature accelerated the rate of moisture absorption and reduced the time required for equilibrium swelling. Exposure to sunlight in solar concentrator deteriorated mechanical properties such as tensile strength and tensile modulus by weakening the fibre–matrix interfacial adhesion and by chain scission.

Blending of Natural Fibres and Thermoplastics by Screwless Extrusion

Natural fibres, such as sisal, flax and woodfibres, are relatively inexpensive and originate from renewable resources. Thermoplastic polymers, such as polypropylene (PP), high density polyethylene (HDPE) and waste plastics, possess shorter manufacturing cycle times and reprocessability. Natural fibre-reinforced thermoplastic composite materials exhibit favourable values of modulus and strength when the fibres are properly compounded with the polymers. Common methods for manufacturing natural fibre-reinforced thermoplastic composites, injection moulding and extrusion, require pre-compounding of the fibres and the thermoplastic due to the large difference in densities of the loose fibres and thermoplastic materials. Development and analysis of a screwless extruder that employs a reliable and low technology process for melt blending natural fibres and thermoplastic polymers is the main objective of this study.

MANUFACTURING FLAX FIBRE-REINFORCED POLYPROPYLENE COMPOSITES BY HOT-PRESSING

The renewable characteristic of natural fibres, such as flax, and the recyclable nature of thermoplastic polymers, such as polypropylene, provide an attractive eco-friendly quality to the resulting composite materials. Common methods for manufacturing natural fibre-reinforced thermoplastic composites, injection moulding and extrusion, tend to degrade the fibres during processing. Development of a simple manufacturing technique for these composites, that minimises fibre degradation, is the main objective of this study. Flax fibres were conditioned, cut into lengths ranging from 1 mm to 30 mm with scissors and a pelletiser, and shaped into randomly oriented mats using a drop feed tower. Polypropylene in sheet form, was added to the fibres to furnish polypropylene/flax/polypropylene sandwiches with a fibre mass fraction of 25%, which were then consolidated by the hot pressing technique. Tensile, flexural and impact properties of these composite sheets were determined as functions of fibre length and processing temperature.

Manufacturing sisal–polypropylene composites with minimum fibre degradation

Natural fibres, such as sisal, flax and jute, possess good reinforcing capability when properly compounded with polymers. These fibres are relatively inexpensive, originate from renewable resources and possess favourable values of specific strength and specific modulus. Thermoplastic polymers have a shorter cycle time as well as reprocessability despite problems with high viscosities and poor fibre wetting. The renewability of natural fibres and the recyclability of thermoplastic polymers provide an attractive eco-friendly quality to the resulting natural fibre-reinforced thermoplastic composite materials. Common methods for manufacturing natural fibre-reinforced thermoplastic composites, injection moulding and extrusion, tend to degrade the fibres during processing. Development of a simple manufacturing technique for sisal fibre-reinforced polypropylene composites, that minimises fibre degradation and can be used in developing countries, is the main objective of this study. Composite sheets with a fibre length greater than 10 mm and a fibre mass fraction in the range 15% to 35% exhibited good mechanical properties.