Effect of Recycling on the Mechanical Properties of Wood Fiber-Polystyrene Composites. II. Sawdust as a Reinforcing Filler

The recycling behavior of sawdust, both hardwood and softwood, filled polystyrene composites was observed by measuring the mechanical properties and dimensional stability under normal conditions (room temperature) as well as extreme ones (e.g., exposure to water at room temperature and boiling temperature, and to heat at +105°C and ?20°C). Mechanical properties and dimensional stability of the original and recycled composites—that is, nontreated and treated ones (e.g., 3% isocyanate, coated fiber-filled and grafted fiber-filled)—are compared under all extreme conditions. the behavior of the recycled composites did not change significantly. Furthermore, treated wood fiber-filled thermoplastic composites offered superior mechanical properties and dimensional stability under all extreme conditions, even after recycling.     

Effect of recycling on the mechanical properties of wood fiber–polystyrene composites. Part I: Chemithermomechanical pulp as a reinforcing filler

The feasibility for recycling composites of polystyrene-hardwood aspen fiber (chemithermomechanical pulp or CTMP) was tested by evaluating the mechanical properties and dimensional stability of the original polymer and the recycled composites. The mechanical properties and dimensional stability of composites were investigated under extreme conditions (e.g., exposure to boiling water and at room temperature as well as exposure to +105°C and −20°C). The influence of coupling agent, e.g., 3% poly[methylene (polyphenyl isocyanate)] (PMPPIC), and various treatments, e.g., fiber coated with 10% polymer +8% PMPPIC and grafted with polystyrene 89.1% add-on, on the properties of the composites have also been studied. Compared with the original composites, the mechanical properties and dimensional stability of the recycled composites did not change significantly even after exposure to extreme conditions. Moreover, the treated composites offered improved properties compared with nontreated and original polymer under all experimental conditions.     

Performance of treated hybrid fiber reinforced-thermoplastic composites under extreme conditions. IV. Use of glass fiber and sawdust as hybrid fiber

The mechanical properties and dimensional stability of hardwood aspen in the form of sawdust and surface-treated glass fiber-polystyrene composites were evaluated under various extreme conditions, e.g., variation in the testing temperature (from +25° to ?20°C), exposure to boiling water and heat in an oven at +105°C. The compatibility of wood fiber with glass fiber and with polystyrene improved by precoating the wood fiber with a coupling agent, e.g., 8% isocyanate, 4% silane and polymer. The mechanical properties of the composites, in particular, treated sawdust/glass fiber-filled composites, increased under extreme conditions in comparison with those filled with nontreated sawdust/glass fiber. Under the same conditions, dimensional stability also supports this observation.     

Surface modification of wood fibers using maleic anhydride and isocyanate as coating components and their performance in polystyrene composites

The effect of surface modification of various wood fibers [e.g. woodflour and chemithermomechanical pulp (CTMP) of hardwood aspen, and woodflour of softwood spruce] by precoating with only maleic anhydride (MA) and/or poly[methylene (polyphenyl isocyanate)] (PMPPIC) in the presence of benzoyl peroxide (BPO) on the mechanical performance of modified fiber-filled polystyrene (PS 201 and PS 525) composites has been studied. The effects of the concentration of fiber, MA, PMPPIC, and BPO on the mechanical properties of the composites have also been evaluated. As opposed to unmodified fiber-filled composites, most of the mechanical properties of the modified fiber-filled composites increased with an increase in the concentration of BPO, MA, and/or PMPPIC up to a certain limit, and then either decreased or levelled off. The properties improved even more when both MA and PMPPIC were used as compared with the use of only one of them. The optimum concentrations of BPO, MA, PMPPIC, and fiber vary according to the wood species, the nature of the fiber, and the type of polystyrene. Compared with woodflour, CTMP is believed to be by far the best as far as the mechanical properties of the modified fiber-filled composites are concerned.     

The Mechanical Properties of Wood Fiber-reinforced Polymethylmethacrylate

Abstract

The mechanical properties, e.g. tensile modulus (at 0.1% strain), tensile strength at maximum point and corresponding elongation and breaking energy, as well as impact strength, of compression molded PMMA and PMMA filled with wood fibers (10%-40% by weight of composite) have been investigated. Optimization of molding conditions, (e.g. temperature, time, pressure and mixing aids) was carried out. In optimum conditions of mixing and molding, the effect of different parameters, (e.g. nature and concentration of coupling agents (isocyanates), coating treatment, nature of wood species in the form of various pulps) on the mechanical properties of the resulting composites were evaluated. PMPPIC having 2%-4% (by weight of polymer) was found to behave as a true coupling agent because modulus as well as the tensile and impact strengths were improved. Moreover, PMPPIC acted as a coupling agent even when it was used for treatment of PMMA and fiber or to precoat the fiber. A distinct effect of the morphology of wood species and fiber-making techniques on the mechanical properties of wood fiber-filled composites was also observed.     

Studies on the preparation and properties of particle boards made from bagasse and PVC. I: Effects of operating conditions

Under study were the mechanical properties of particle boards comprised of ground sugarcane bagasse, PVC, and poly{methylene (polyphenyl isocyanate)} [PMPPIC]. The effects of different parameters, e.g. mixing temperature, molding conditions - platen temperature, time and pressure, particle size of bagasse, concentration of PVC and PMPPIC, as well as dilution of PMPPIC, on the mechanical properties of the resulting particle boards were also investigated. In general, the properties of particle boards change with the variation of mixing and molding conditions. A mixing temperature of 175°C and molding conditions [platen temperature, 190°C; time, 10 min; and pressure, 3.8 MPa] were believed to be optimal conditions of compounding particle boards. Both the mechanical properties and the density of particle boards of bagasse with a mesh size of 60, improved up to 20 weight % of PVC and 10 weight % of PMPPIC.     

Influence of Polar Monomers on the Performance of Wood Fiber Reinforced Polystyrene Composites. I. Evaluation of Critical Conditions

Abstract

Wood fibers and nonpolar thermoplastics, e.g. polystyrene, are not the ideal partner for the preparation of composites because of a wide difference in their polarity. In the present study, polarity of the polystyrene was modified by the introduction of a—COOH group, through the reaction with maleic anhydride (MA) in the presence of an initiator (benzoyl peroxide: BPO) in a roll mill at the elevated temperatures. Optimum conditions for the preparation of polar polystyrene have been investigated. The temperature of the roll mill, i.e., the reaction temperature, and reaction time varied between 160–175°C and 10–15 min., respectively. The concentrations of the monomer, (MA) as well as the initiator (BPO), also varied: 0–10% and 0–2% (by weight of polymer), respectively. The mechanical properties of chemithermomechanical pulp (CTMP)-filled modified polystyrenes were evaluated. The effect of 3% coupling agent [e.g. poly(methylene (polyphenyl isocyanate))] (PMPPIC) on the mechanical properties of the same composites was also determined.

Generally, mechanical properties of the composite materials were enhanced when modified polymers were used as base polymers. Moreover, the extent of the improvement in mechanical properties depends on the reaction temperature and time, as well as on the concentrations of the monomer (maleic anhydride) and initiator. Maximum improvements in mechanical properties occur when the temperature was maintained at 175°C for 15 min. In addition, preferred concentrations of both the monomer and initiator were found to be 5% and 1% (by polymer weight), respectively. Once again, properties were further accelarated when coupling agent (e.g. PMPPIC) was used in addition to the modified polystyrene. The improvements in mechanical properties (over those of the original polymer and those of composites containing unmodified polymers) indicate that the compatibility between hydrophilic cellulosic fiber and hydrophobic polymer has increased.     

Use of grafted aspen fibers in thermoplastic composites: IV. Effect of extreme conditions on mechanical properties of polyethylene composites

Hardwood fibers of aspen in the form of chemithermo-mechanical pulp (CTMP) have been used as reinforcement in linear low density polyethylene (LLDPE). The effect of composite treatment (immersion in boiling water, heat exposure at 105°C for seven days or at a temperature of −40°C) on resulting mechanical properties were evaluated. The grafted aspen CTMP composites showed by far the best results with regard to secant modulus, tensile strength, energy, and strain when compared to those of wood flour, mica or glass–fiber filled LLDPE, as well as to virgin LLDPE. Finally, the dimensional stability of CTMP aspen-filled LLDPE composites immersed for four hours in boiling water was better than that of mica or glass–fiber filled LLDPE.     

Effect of pyrolysis temperature on the mechanical evolution of SiCf/SiC composites fabricated by PIP

Three types of SiC_f/SiC composites with a four-step three-dimensional SiC fibre preform and pyrocarbon interface fabricated via precursor infiltration and pyrolysis at 1100 °C, 1300 °C, and 1500 °C were heat-treated at 1300 °C under argon atmosphere for 50 h. The effects of the pyrolysis temperature on the microstructural and mechanical properties of the SiC_f/SiC composites were studied. With an increase in the pyrolysis temperature, the SiC crystallite size of the as-fabricated composites increased from 3.4 to 6.4 nm, and the flexural strength decreased from 742 ± 45 to 467 ± 38 MPa. After heat treatment, all the samples exhibited lower mechanical properties, accompanied by grain growth, mass loss, and the formation of open pores. The degree of mechanical degradation decreased with an increase in the pyrolysis temperature. The composites fabricated at 1500 °C exhibited the highest property retention rates with 90% flexural strength and 98% flexural modulus retained. The mechanism of the mechanical evolution after heat treatment was revealed, which suggested that the thermal stability of the mechanical properties is enhanced by the high crystallinity of the SiC matrix after pyrolysis at higher temperatures.     

Pultruded fiber-reinforced polyurethane-toughened phenolic resin. II. Mechanical properties,thermal properties,and flame resistance

A novel process has been developed to toughen phenolic resin by polyurethane for fiber-reinforced pultruded composites. The mechanical properties of the composites (tensile strength, flexural strength, and notched Izod impact strength) approach maximum values at 10 wt% of the blocked polyurethane content. The fabricated composites show good mechanical properties and possess low void fraction. Notched Izod impact strength of the composite (with 5 wt% polyurethane content) increases by more than 30% compared to the virgin composite. The thermogravimetric analysis (TGA) showed that the temperature for the 5% weight loss of the phenolic/polyurethane copolymer decreases with the increasing of the polyurethane content; however, the thermal degradation temperature is still higher than 350°C. Differential scanning calorimetric analysis (DSC) showed that the onset point of copolymer is 20°C higher than that of the virgin one. The presence of the blocked polyurethane may hinder the polymerization of phenolic resin. The modified composite shows excellent dimensional stability. The copolymer composite also possesses good fire resistance. © 1996 John Wiley & Sons, Inc.     

Effect of interphase on mechanical properties and microstructures of 3D Cf/SiBCN composites at elevated temperatures

Interphase between the fibers and matrix plays a key role on the properties of fiber reinforced composites. In this work, the effect of interphase on mechanical properties and microstructures of 3D C_f/SiBCN composites at elevated temperatures was investigated. When PyC interphase is used, flexural strength and elastic modulus of the C_f/SiBCN composites decrease seriously at 1600°C (92 ± 15 MPa, 12 ± 2 GPa), compared with the properties at room temperature (371 ± 31 MPa, 31 ± 2 GPa). While, the flexural strength and elastic modulus of C_f/SiBCN composites with PyC/SiC multilayered interphase at 1600°C are as high as 330 ± 7 MPa and 30 ± 2 GPa, respectively, which are 97% and 73% of the values at room temperature (341 ± 20 MPa, 41 ± 2 GPa). To clarify the effect mechanism of the interphase on mechanical properties of the C_f/SiBCN composites at elevated temperature, interfacial bonding strength (IFBS) and microstructures of the composites were investigated in detail. It reveals that the PyC/SiC multilayered interphase can retard the SiBCN matrix degradation at elevated temperature, leading to the high strength retention of the composites at 1600°C.     

Optothermal analysis of polymer composites

A number of thermographic techniques under optical-radiation heating are described for the nondestructive evaluation of different kinds of fiber-filled polymer-based composites. Shallow delaminations within carbon-fiber reinforced laminates can be detected by this method under wide-area surface heating to 5 or 10° above ambient. A number of image-processing algorithms are described for improving the visibility of subsurface defects. Spot-heating techniques are presented for the characterization of fiber concentration, distribution, and orientation in carbon or steel fiber-filled composites. Particular emphasis is given to the possibility of mapping fiber-orientation properties at gradually deeper layers below the surface. These optothermal techniques appear to be a convenient tool for the inspection of opaque composites in terms of rapidity, lack of sample preparation requirement, and simplicity both in its implementation and in the interpretation of results.     

Composite Molded Products Based on Recycled Thermoplastics and Waste Cellulosics. I. Peat Moss-Recycled Pe Composites

Effects of three different modified (i.e., chlorinated, chlorosulfonated, and maleated) polyethylenes (PEs) on the mechanical properties and dimensional stability of recycled PE composites filled with biomass (peat moss) have been investigated at room temperature and after exposure to boiling water for 24 h. From the experimental results, it is suggested that differently modified PEs play an important role in improving the physicomechanical properties of the peat moss-filled recycled PE composites, even after exposure to boiling water. However, maleated PE is by far the best coupling agent as far as mechanical properties and dimensional stability of the peat moss-filled recycled PE is concerned. The effects of concentrations of peat moss and coupling agent (i.e., chlorinated PE) on the properties of the composites have been statistically analyzed based on an experimental design and on an empirical quadratic model.     

High-temperature aging of halar film. I. Study of physicochemical changes

A heat-aging study was undertaken to determine the physicochemical changes in an experimental Halar film [about 80% alternating 1:1 copolymer of ethylene (E) and chlorotrifluoroethylene (CTFE)] as a result of exposure to elevated temperatures in air. This work was intended to evaluate how Halar would behave upon exposure to high temperatures as might be the case in wire and cable coating or other similar applications. Samples of Halar film were aged (unstressed) in air at three different temperatures (150, 175, and 200°C) for a period of up to 1000 h and then characterized with respect to yellowness index, molecular weight, chemical structure changes, crystalline characteristics, thermal behavior, and tensile properties. The results point out no significant deterioration of properties as a result of aging at 150 or 175°C for 40 days. Actually the exposure at 150 or 175°C increases the molecular weight slightly and enhances crystallinity, which improve the dimensional stability of Halar. Extended exposures at 200°C increased the yellowness index and caused physical distortion of the film. The rest of the properties either remained the same or showed some improvement.     

Ultra-high-temperature mechanical behaviors of two-dimensional carbon fiber reinforced silicon carbide composites: Experiment and modeling

Carbon fiber reinforced silicon carbide (C/SiC) composites are enabling materials for components working in ultra-high-temperature extreme environments. However, their mechanical properties reported in the literature are mainly limited to room and moderate temperatures. In this work, an ultra-high-temperature testing method for the mechanical properties of materials in inert atmosphere is presented based on the induction heating technology. The flexural properties of a 2D plain-weave C/SiC are studied up to 2600 °C in inert atmosphere for the first time. The deformation characteristics and failure mechanisms at elevated temperatures are gained. Theoretical models for the high-temperature Young’s modulus and tensile strength of 2D ceramic matrix composites are then developed based on the mechanical mechanisms revealed in the experiments. The factors contributing to the mechanical behaviors of C/SiC at elevated temperatures are thus characterized quantitatively. The results provide significant understanding of the mechanical behaviors of C/SiC under ultra-high-temperature extreme environment conditions.     

Mechanical and microstructural analysis of geopolymer composites based on metakaolin and recycled silica

This paper evaluated mechanical and thermal stability of alkali-activated materials obtained from metakaolin and alternative silica sources, such as rice husk ash (RHA) and silica fume (SF), and were reinforced with recycled ceramic particles (RP) obtained by grinding bricks. Specimens were produced, and after 7 days of curing, they were exposed to temperatures between 300 and 1200°C to determine the influence that different percentages of RP had on the mechanical behavior and microstructure of the produced composites. The results showed a reduction in the linear contraction by 10.22% with 20 wt% RP and that the reinforcing materials improved the mechanical performance of the geopolymers after exposure to high temperatures; the compressive strengths reached 137.7 (±11.4)  MPa after being exposed to 1200°C for the matrix based on RHA and 180.6 (±19.15) MPa after being reinforced with 20 wt% RP. The improvement was mainly due to densification and the formation of crystalline products such as leucite, kalsilite, and mullite.     

Improving delamination resistance of carbon fiber reinforced polymeric composite by interface engineering using carbonaceous nanofillers through electrophoretic deposition: An assessment at different in-service temperatures

In this article, modification of carbon fiber surface by carbon based nanofillers (multi-walled carbon nanotubes [CNT], carbon nanofibers, and multi-layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in-situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter-laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in-situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites.     

Durable glass–epoxy composites cured at low temperatures—Effects of thermal cycling,UV irradiation and wet environment

Glass-fibre-epoxy composites cured with oligomeric polyaminophenolic agents have shown good dimensional stability during thermal cycling at temperatures over 100°C, even if their curing is carried out at room temperature. It was therefore believed important to evaluate their behaviour in different environmental conditions. Their good mechanical characteristics are maintained after saturation with water, UV irradiation, and thermal cycling between 0 and 110°C. From the following tests the environmental resistance is clearly higher than that of composites cured with other aminic agents.     

Properties of Geopolymer Composites Reinforced with Basalt Chopped Strand Mat or Woven Fabric

Geopolymers or polysialates are inorganic polymeric, ceramic‐like materials composed of alumina, silica, and alkali metal oxides that can be made without any thermal treatment. Additions of reinforcing phases vastly improve the mechanical properties and high‐temperature stability of the geopolymer. The processing and mechanical properties of both chopped strand mat as well as 2‐D woven fabric‐reinforced potassium geopolymer composites have been evaluated. Hand lay‐up and hydraulic press processing methods were used to produce composite panels. The room‐temperature tensile and flexural strength of chopped strand mat composites was 21.0 ± 3.1 and 31.7 ± 4.4 MPa, respectively, while those of basalt weave‐reinforced geopolymer composites reached 40.0 ± 5.9 and 45.2 ± 9.3 MPa, respectively. Composite microstructures were examined using optical microscopy as well as scanning electron microscopy (SEM). Mass, volume, and porosity fractions were also determined. The effect of high‐temperature treatments at 25°C, 300°C, 600°C, and 800°C were analyzed. Finally, Weibull statistical analysis was performed, which showed an increase in reliability when a reinforcement phase was added to K‐geopolymer.     

Preparation and mechanical properties of the 2.5D ASf/ZrO2 composites after high-temperature heat treatment

In the paper, the aluminosilicate fiber-reinforced zirconia (AS_f/ZrO₂) ceramic composites were successfully fabricated by polymer impregnation and pyrolysis (PIP) method. The microstructure and high-temperature mechanical properties of the original composites were well studied. The results revealed that the composites could maintain the stability of microstructure at 1000 °C. The flexural strength increased from 58.82 ± 2.83 MPa to 88.74 ± 6.20 MPa and the flexural modulus increased from 29.26 ± 4.67 GPa to 40.76 ± 8.76 GPa. The thermal exposure improved the interfacial bonding and made the load transfer more effective. After heat treatment from 1200 °C to 1400 °C, the flexural strength gradually declined due to the crystallization of the AS fibers and ZrO₂ matrix, while the flexural modulus increased in a completely different trend. After heat treatment at 1400 °C, the composites could maintain a flexural strength of 66.95 ± 4.24 MPa with a flexural modulus of 60.42 ± 7.25 GPa. But the fracture mode gradually evolved to brittleness.