Fiber-reinforced Unsaturated Polyester Research Articles

Improvement of Interfacial Adhesion in Natural Plant Fiber-reinforced Unsaturated Polyester Composites: A Critical Review

Natural plant fiber-reinforced unsaturated polyester (UPE) composites have lower strengths and absorb more water than glass fiber-UPE composites because of the incompatibility between hydrophilic natural fibers and hydrophobic UPE. The good interfacial adhesion between the natural fibers and the UPE matrix is essential for the superior mechanical properties and good water resistance for the natural fiber-UPE composites. Extensive work has been done on the improvement of the interfacial adhesion. This paper reviews various physical and chemical methods used in the treatments of natural fibers for the improvement of the interfacial adhesion. Physical methods include plasma and heat treatments of natural fibers. Chemical methods include alkaline treatments, acetylation, and benzoylation of natural fibers, the use of coupling agents, and in-situ polymerizations of acrylic acid, acrylonitrile, and styrene in the presence of natural fibers. Mechanisms by which these physical and chemical methods improve the interfacial adhesion between the natural fibers and the UPE matrix are discussed in detail. The effects of these methods on the improvements of mechanical properties and water resistance of the resulting natural fiber-UPE composites under the best conditions reported are also reviewed.

Mechanical and Thermal Properties of Hemp Fiber-Unsaturated Polyester Composites Toughened by Butyl Methacrylate

Hemp fiber-reinforced unsaturated polyester (UPE) composites were prepared by hand lay-up compression molding. The UPE resins were modified with butyl methacrylate (BMA) to improve the flexibility and toughness of the hemp-UPE composites. The results indicate that the toughness of the composites significantly increased as BMA usage increased. Compared to the unmodified UPE composites, the composites obtained from BMA-modified UPE resins had 27.4, 63.0, and 36.6% greater elongation at break, flexural strain, and impact strength, respectively. The optimum BMA usage to achieve an adequate balance of stiffness and toughness is 20 to 30%. Dynamic mechanical analysis (DMA) indicated that incorporation of BMA significantly decreased the storage modulus and glass transition temperature of the composites and increased its damping parameter due to the introduction of flexible segments into the UPE resins. Thermogravimetric analysis showed that the thermal stability of the composites decreased slightly following the incorporation of BMA. Scanning electron microscopy images of the impact-fractured surfaces of the composites revealed that BMA incorporation improved interfacial adhesion between hemp fibers and UPE matrices and that the main mechanism for the increase in the toughness of the composites was the added ductility of the matrices.

Investigation of bamboo pulp fiber-reinforced unsaturated polyester composites

AbstractMechanical pulp fibers (MPFs) and chemical pulp fibers (CPFs) from moso bamboo have been characterized in terms of their length and width distributions, and their reinforcing effects in unsaturated polyester (UPE) composites have also been investigated. CPF-UPE composites had much higher tensile strength, flexural strength, and flexural modulus than MPF-UPE composites. CPF-UPE composites also absorbed less water than MPF-UPE composites. Treatments of the fibers with a combination of 1,6-diisocyanatohexane (DIH) and 2-hydroxyethyl acrylate (HEA) significantly increased the tensile strength, flexural strength, flexural modulus, and water resistance of the resulting composites. Fourier transform infrared and X-ray photoelectron spectroscopy analyses indicated that DIH-HEA was bound onto bamboo fibers (BFs) via carbamate linkages. The scanning electron microscopy images of the tensile-fractured surfaces of the composites revealed that the DIH-HEA treatments for BFs greatly improved the interfacial adhesion between the fibers and UPE resins.

Adhesion analysis of non-woven natural fibres in unsaturated polyester resin

The presence of wool fibres in non-woven Alfa fibres sheet was investigated as a mean of improving adhesion of Alfa fibre-reinforced unsaturated polyester composite. FT-IR and Raman spectroscopy results revealed that such improvement could occur by a decrease in the hydrophilic character of the Alfa fibres owing to the presence of wool fibres. Hence, physical and chemical interactions could happen between the reinforcement and the matrix as demonstrated by FT-IR and Raman spectroscopy results. Tensile testing performed on this composite confirmed that such adhesion could occur according to its excellent specific parameters despite of its low tensile strength attributed to a higher fibre to fibre contact of wool fibres.

Tensile Properties of Pineapple Leaf Fibre Reinforced Unsaturated Polyester Composites

In recent years natural fibres such as sisal, jute, kenaf, pineapple leaf and banana fibres appear to be the outstanding materials which come as the viable and abundant substitute for the expensive and non-renewable synthethic fibre. This paper investigate the effect of fibre length and fibre content on the tensile properties of pineapple leaf fibre (PALF) reinforced unsaturated polyester (UP) composites. PALF as reinforcement agent will be employed with UP to form composite material specimens. The various of fiber length (<0.5, 0.5–1, and 1-2 mm) and fibre content (0, 5, 10 and 15 % by volume) in UP composite have been studied. The fabrication of PALF/UP composites used hand lay-up process, and the specimens for tensile test prepared follow the ASTM D3039. The result obtained from this study show that the 1-2 mm fibre length has higher tensile strength (42 MPa) and tensile modulus (1344 MPa) values compared to fibre length of <0.5 mm (30 MPa and 981 MPa) and 0.5-1 mm (35.40 MPa and 1020 MPa) respectively. Meanwhile, for the effect of various fibre content in study has shown that the increase of fibre content has decreased in tensile strength dan tensile modulus of composites. The increase of fibre content due to poor interfacial bonding and poor wetting of the fibre by unsaturated polyster. The treatment of natural fibre are suggested in order to improve the interfacial adhesion between natural fibre and the unsaturated polyester.

The effect of argon and air plasma treatment of flax fiber on mechanical properties of reinforced polyester composite

Flax fibers were modified by argon and air atmospheric pressure plasma treatments to improve the mechanical properties of flax fiber-reinforced unsaturated polyester composites. Plasma treatments were carried out at plasma powers of 100, 200, and 300 W. Both plasma surface treatments were conducted to improve the tensile strength, tensile modulus, flexural strength, flexural modulus, interlaminar shear strength (ILSS), Mode I interlaminar fracture toughness (GIC), and Mode II interlaminar fracture toughness (GIIC). Moreover, the maximum improvement in the mechanical properties was obtained after air plasma treatment of flax fiber at a plasma power of 300 W. Tensile strength, flexural strength, ILSS, GIC, and GIIC values of flax fiber-reinforced polyester composites increased by nearly 34%, 31%, 39%, 35%, and 42%, respectively. However, for argon plasma-treated flax fiber-reinforced polyester composites, the mechanical properties of composite increased up to argon plasma power of 200 W.

Effects of Alkali Treatment and Polyisocyanate Crosslinking on the Mechanical Properties of Kraft Fiber-Reinforced Unsaturated Polyester Composites

The effects of alkali treatment and polyisocyanate crosslinking on the mechanical properties of kraft fiber-reinforced UPE composites were investigated by means of tensile evaluation, SEM analysis, and XRD analysis. The results indicated that the alkali treatment decreased the tensile strength of the prepared composite before aging from 121 MPa to 97 MPa due to the decreased degree of crystallinity of the alkali-treated kraft fiber. Polyisocyanate crosslinking could apparently improve the mechanical properties and stability in terms of a 43% increase of non-aged tensile strength and 52% increase of hydrothermal-aged tensile strength compared with the controlled composite without crosslinking modification, which was attributable to the formation of strong chemical bonding between the interfaces of kraft fiber and polyester.

Tensile Properties of Kenaf Yarn Fibre Reinforced Unsaturated Polyester Composites at Different Fibre Orientations

This paper reported the study of tensile properties of kenaf yarn fibre reinforced unsaturated polyester (UP) composites at different fibre orientations, i.e. 0o, ±45o and 90o. It is concluded that composites with 0o orientation show higher strength and stiffness than composites with ±45o and 90o angle fibre orientation. The highest value of stress is 29 MPa for 0o loading direction followed by ±45o loading direction (28 MPa) and 90o loading direction has the lowest stress value of 6 MPa. Tensile modulus results revealed the highest value of 10.61 GPa for 0o loading direction and the tensile modulus for 45o orientation of loading direction is 5 GPa, followed by the modulus for 90o of fibre loading direction of 1.2 GPa; which is the lowest.

Tensile Strength of Untreated Napier Grass Fibre Reinforced Unsaturated Polyester Composites

This paper describes the experimental investigation of the tensile strength of untreated Napier grass fibre reinforced polyester composites. Napier grass fibres were extracted trough conventional water retting process and used as reinforcing materials in the polyester composite laminates. Tensile tests were then conducted for the composite specimens from the laminates at 25% fibre loading using the electronic extensometer setup to obtain the tensile properties. The results show significant differences in tensile strength between random short fibres laminates and random long fibre laminates with the long fibres yield almost 45 % higher in the strength. The laminates also show higher maximum strength compared to other commonly available natural fibre composites with over 70 % increase in the maximum strength compared to the short kenaf fibre reinforced composites.

Interfacial microstructure and properties of carbon fiber-reinforced unsaturated polyester composites modified with carbon nanotubes

To improve the interfacial properties in carbon fiber (CF)-reinforced unsaturated polyester (UP) composites, we directly introduced functionalized carbon nanotubes dispersed in the fiber sizing onto the fiber surface. For comparing the influence of polymer type on sizing effect, two different polymers (UP MR13006 and water-soluble epoxy (EP)) were used to prepare sizing agent. Morphology and surface energy of CFs were examined by scanning electron microscopy and dynamic contact angle analysis test. Tensile strength was investigated in accordance with ASTM standards. Mechanical properties of the composites were investigated by interlaminar shear strength (ILSS) and impact toughness. Test results indicate that TS, ILSS, and impact toughness were enhanced simultaneously. For UP matrix, the sizing agent containing UP has better reinforcing and toughening effect than the sizing agent containing water-soluble EP.

Thermal behavior of E-glass fiber-reinforced unsaturated polyester composites

The aim of this work is to study the behavior of E-glass fiber unsaturated polyester composites, subjected to moderate and high temperatures. The obtained results show that the chemical, physical and mechanical properties of the resin and the composite change with the rise of the temperature. A thermogravimetric analysis (TGA) revealed that the thermal degradation of the composite occurs in two steps: the first between 130 and 200°C and the second between 250 and 440°C.The characterization of the resin and the composite, after heating, revealed that at moderate temperatures (lower than 100°C) an improvement of the properties of materials is observed. For high temperatures but lower than the temperature of decomposition (Td), the mechanical strength of the resin does seem to be very affected, even improved for certain cases. For these temperatures, the composite presents some fractures of the fiber–matrix interfaces, which causes losses in strength and ductility.When the temperature reaches the temperature of decomposition (Td), a fall of the mechanical properties was recorded for both resin and composite.

Effect of coupling agents on the properties of bamboo fiber-reinforced unsaturated polyester resin composites

In this study, biocomposites were prepared by using an unsaturated polyester and Luong bamboo fibers (BFs). Fibers separated from bamboo body by mechanical method had size distribution mainly between 0.24 and 0.40 mm diameter and 1–2.5 cm length. Some factors having effect on properties of materials, such as fiber content, type, and concentration of coupling agents were also studied. As a result, composite materials showed good properties at 90 phr of BFs that were modified by 0.7% vinyl-functional silane coupling agent.

Tensile and Impact Properties of Different Morphological Parts of Sugar Palm Fibre-Reinforced Unsaturated Polyester Composites

The present study investigated the tensile and impact behaviour of unsaturated polyester composites reinforced by fibre from different parts of the sugar palm tree. Sugar palm fibre i.e. sugar palm frond (SPF), sugar palm bunch (SPB), black sugar palm fibre ( ijuk) and sugar palm trunk (SPT) which have high content of cellulose, low density, abundance and low cost, have the potential for polymer reinforcement. All composites were fabricated and labelled as SPF/PE, SPB/PE, ijuk/PE and SPT/PE. It was found that SPF/PE had the highest tensile strength which was 15.179 MPa (±2.425) followed by SPB/PE, ijuk/PE and SPT/PE with 12.809 MPa (±1.580), 11.473 MPa (±0.536) and 9.817 MPa (±1.890) respectively. For the impact strength analysis, SPF/PE showed the highest value (8.091 kJ m-2). Generally, SPF/PE had better tensile and impact properties than the other composites, due its high cellulose content.

Preparation and characterization of graft copolymerized Cannabis indica L. fiber-reinforced unsaturated polyester matrix-based biocomposites

In present manuscript, Cannabis indica L. fibers were graft copolymerized in air with acrylonitrile using redox initiator system in order to improve the mechanical properties of Cannabis indica L/unsaturated polyester composites. The various reaction parameters such as time, temperature, pH, concentration of initiator, nitric acid and monomer were optimized to get maximum graft yield. The kinetics of the graft copolymerization of acrylonitrile was also studied. The physical, chemical and thermal properties of grafted fibers have also been investigated. Further, both raw and grafted fibers in particle form with different loading (10, 20, 30 and 40%) were used as reinforcement to prepare unsaturated polyester matrix-based green polymer composites. Effects of particles loading on mechanical properties like tensile, compressive and flexural strength have been determined and were found to affect significantly by percent loading. A considerable increase in mechanical properties has been observed after reinforcing the neat resin with grafted particles. Further scanning electron microscopic, thermogravimetric analysis, differential scanning calorimetric and chemical resistance measurements were used as characterization techniques to evaluate different behavior of these polymer composites.

Evaluation of Water Absorption Damage in Hemp Fibre Reinforced Unsaturated Polyester Composites by the Nanoindentation Testing

The effect of water absorption damage on the nanohardness and elastic modulus properties of the hemp fibre reinforced unsaturated polyester composites (HFRUPC) have been investigated using the nanoindentation testing. HFRUPC specimens containing 0, 28, 37 and 45 fibre wt.%, corresponding to neat UP, UP/3 layer hemp, UP/4 layer hemp and UP/5 layer hemp, respectively, were prepared and subjected to water immersion tests in a de-ionised water bath at 25 C and 100 C for different time durations. Elastic modulus and nanohardness properties of water immersed specimens subjected to both aging conditions are evaluated and compared alongside dry composite specimens. The elastic modulus and nanohardness properties of HFRUPC specimens were found to increase with the increase in fibre wt.% and decrease with increase in percentage moisture uptake. Nanoindentation is an effective technique to measure elastic modulus and hardness on a nanometer range. Its attractiveness lies largely from the fact that nanomechanical properties can be determined directly from indentation load and displacement measurements. SEM study was also applied to relate the decrease in properties as a result of water uptake in hemp composites.

Effects of Surface Treatments on Mechanical Properties and Water Resistance of Kenaf Fiber-Reinforced Unsaturated Polyester Composites

Effects of surface treatments on the strength and water resistance of kenaf fiber-reinforced unsaturated polyester (UPE) composites were investigated. A new coupling agent that consists of 1,6-diisocyanato-hexane (DIH) and 2-hydroxylethyl acrylate (HEA) was investigated for surface treatments of kenaf fibers. The surface treatments were found to significantly enhance the tensile strength, modulus of rupture, modulus of elasticity, and water resistance of the resulting kenaf–UPE composites. Fourier transform infrared spectroscopy (FTIR) confirmed that DIH-HEA was covalently bonded onto kenaf fibers. Scanning electron microscopy (SEM) images of the composites revealed that chemical treatment of kenaf fibers with a combination of DIH and HEA improved the interfacial adhesion between kenaf fibers and UPE resin in the DIH–HEA-treated kenaf–UPE composites. The mechanisms by which the chemical treatment of kenaf fiber surfaces improved strength and water resistance of the resulting kenaf–UPE composites were discussed.

Variations of mechanical properties of jute/polyester composite aged in various media

Woven roving jute fiber-reinforced unsaturated polyester composites were subjected to water absorption tests in order to study the effects of water ageing on the mechanical properties. Composite specimens were immersed in distilled water and salt water up to 2736 h. The water absorption of specimens reached to an equilibrium level after an immersion time of 300 h. It was observed that tensile, flexural, and interlaminar shear strengths (ILSSs) of jute/polyester composites decreased depending on the immersion time. The ILSS values of the composites were reduced by more than 53% for both the distilled water and the salt water after an immersion time of 2736 h.

Effect of water absorption on pultruded jute/glass fiber-reinforced unsaturated polyester hybrid composites

The use of natural fibers in polymer composites has given renewed interest to the development of green composites today. However, the moisture absorption of natural fibers gives serious concern, especially for their potential outdoor applications. This article reports the study results on the water absorption of pultruded jute/glass fiber-reinforced unsaturated polyester hybrid composites, which was subjected to various water conditions and their effects on its mechanical properties. Water absorption tests were performed by immersing composite specimens into three different water conditions, namely: distilled water, sea water, and acidic water, which were at room temperature, for a period of 3 weeks. The characteristic parameter of diffusion coefficient ( D) and maximum moisture content ( Mm) were determined from the obtained water absorption curves. The water absorption behavior of the glass/jute fiber-reinforced unsaturated polyester hybrid composite was found to follow a non-Fickian behavior. The effects of the various aqueous environments on the flexural and compression characteristics were investigated in this study. The flexural and compression properties were found to decrease with an increasing percentage of water uptakes.

Effect of low-profile additives on thermo-mechanical properties of glass fiber-reinforced unsaturated polyester composites

Low profile additives (LPA) are thermoplastics particles incorporated into unsaturated polyester (UP) resin in order to improve the surface finish of fiber glass/UP composites by shrinkage compensation. They are widely used in automotive applications where high-quality surface finish is required. In this article, the effect of low-profile additives on the thermo-mechanical properties of resin transfer molded fiber glass/UP panels is investigated. A combination of poly vinyl-acetate and poly methyl-methacrylate additives was tested with three concentrations (0%, 10%, and 40%). The flexural and shear properties were measured by three-point bending and short-beam tests. Thermo-mechanical and dynamic mechanical analyses were performed to measure the coefficient of thermal expansion and the glass transition temperature. The mechanical properties as well as the coefficient of thermal expansion were reduced upon addition of low-profile additives, whereas the glass transition temperature was improved with the content of low profile additives due to a better compatibility of the LPA/UP system.

Comparative Study of Physical Properties Based on Different Parts of Sugar Palm Fibre Reinforced Unsaturated Polyester Composites

This research was conducted to evaluate the potential of sugar palm residue as a raw material to produce the new green composites. The physical properties of sugar palm fibre reinforced unsaturated polyester composites from different part which are sugar palm frond (SPF/PE), sugar palm bunch (SPB/PE), sugar palm trunk (SPT/PE) and black sugar palm fibre (ijuk/PE) were studied. Samples were submerged in distilled water for 24 hours. The water absorption and thickness swelling were investigated in order to determine the dimensional stability of the composites. It is found that SPF/PE showed the higher value of water absorption and thickness swelling which are 1.57%, and 1.56% followed by SPB/PE (1.35%, 1.11%), ijuk/PE (0.65%, 0.76%) and SPT/PE (0.39%, 0.50%). Generally, this investigation is valuable for researchers in order to evaluate the potential and some possible application of sugar palm residues as a new natural composites product.