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.     

Polylactide compositions. Part 1: Effect of filler content and size on mechanical properties of PLA/calcium sulfate composites

Starting from calcium sulfate (gypsum) as a fermentation by-product of lactic acid fermentation, novel high performance composites have been produced by melt-blending polylactide (PLA) and previously dried calcium sulfate hemihydrate in a Brabender bench scale kneader at 190 °C. Due to PLA sensitivity towards hydrolysis, it has first been demonstrated that formation of β-anhydrite II (AII) by adequate thermal treatment of calcium sulfate is a prerequisite. Then, the effect of filler content and mean diameter on thermal, mechanical and impact properties has been examined together with the morphology of the resulting materials. It shows that high tensile performances and impact strength are maintained up to a filler content of 20 wt% without any increase of PLA crystallinity. Interestingly enough and provided that AII particles with a mean diameter of ca. 10 μm were considered as PLA fillers, tensile and impact properties proved to be maintained at a very acceptable level at filler content as high as 50 wt%. Such remarkable mechanical behavior can be accounted for by the excellent filler dispersion throughout the polyester matrix and much favorable interactions between CaSO₄ particles and ester functions of PLA chains as evidenced by the use of predictive mathematical models for composite mechanical properties and SEM-BSE imaging of fractured surfaces.     

Effect of graphite nanoplatelets on the mechanical properties of alumina-based composites

Al₂O₃-based composites using exfoliated graphite nanoplatelets (xGnPs) have been developed by powder metallurgy (PM) route using both conventional as well as spark plasma sintering (SPS) processes. Al₂O₃-0.2, 0.5, 0.8, 3 and 5 vol% xGnP composites have been developed, and the effect of the addition of xGnP on the density, hardness, fracture toughness and wear behaviour of the various Al₂O₃-xGnP composites have been analyzed. Conventional sintering was done at a temperature of 1650 °C for 2, 3 and 4 h in inert atmosphere, whereas SPS was carried out at 1450 °C under 50 MPa pressure for 5 min. A uniform dispersion of the xGnP in the Al₂O₃ matrix was observed in the composites upto the addition of 3 vol% xGnP. Results indicate that a significant improvement in hardness, wear resistance and fracture toughness of the composites could be achieved by using xGnP as nanofiller. The hardness and fracture toughness of the composites developed by both conventional sintering and SPS show an increase upto the addition of 3 and 0.8 vol% xGnP respectively. The wear resistance of the composites also shows significant improvement upto the addition of 3 vol% xGnP. The composites developed by SPS have been found to possess superior mechanical properties as compared to the composites developed by conventional sintering. The improvement in the mechanical properties can be attributed to the strong interaction between the xGnP and the Al₂O₃ matrix at the interfaces and to the toughening mechanisms such as crack bridging and crack deflection.     

Effect of reinforcement type on the mechanical properties of polypropylene composites

The possible reinforcing effects of six different types of filler particles on composites based on the thermoplastic polypropylene have been examined. It is found that significant increases in elastic modulus and tensile strength can be obtained by addition of ≥ 10 percent by volume of glass fibers. Ceramic whiskers, based on alumina and silicon carbide, also lead to increases in modulus but to decreases in strength and ductility. Additional measurements were made with composites prepared from two sizes of spherical glass beads and from carbon spheres. For the glass beads, an increase in modulus was obtained but strength and elongation to fracture decreased. Carbon spheres were ineffective as a reinforcing agent. The possible effects of nonuniform mixing, of size and shape of filler particles, and of surface coatings are discussed.     

Effect of thermal exposure on the properties of phenolic composites: Dynamic mechanical analysis

Changes in the dynamic response of glass‐reinforced phenolic composites following thermal exposure at 180^oC for periods of time up to 28 days were monitored using dynamic mechanical analysis. Four phenolic resins were investigated: a resol/novolac blend, a phenolic–furan novolac/resol graft copolymer, a novolac, and a resol. Reactive blending and copolymerization of phenolic resins are currently being investigated to determine if these techniques will produce phenolic resins (and composites) that have improved impact properties and retain the excellent high‐temperature properties of resol and novolac phenolic resins. The results indicate that thermal aging at 180^oC for 1 day led to a more complete cure of all four phenolic resins as indicated by an increase in the temperature of the maximum of plots of both loss modulus (E″) and tan δ versus temperature. The storage modulus (E′) of the composites at 40^oC varied little following thermal aging at 180^oC for 1 day but decreased with increasing exposure time for samples aged 2, 7, and 28 days. Thermal aging led to an increase in E′ at higher temperatures and the magnitude of E′ at a given temperature decreased with increasing exposure time. The magnitude of E″ and tan δ decreased with aging time for all resins, although E″ and tan δ were larger for the blend and copolymer composites than for the novolac and resol composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 385–395, 2001     

Effect of 3-propionylthio-1-propyltrimethoxylsilane on structure,mechanical, and dynamic mechanical properties of NR/silica composites

Blocked mercaptosilane possessing two functionally active end groups can chemically react with both silica and rubber leading to significant improvement in silica-filled vulcanizate products. The effect of the novel blocked mercaptosilane (3-propionylthio-1-propyltrimethoxylsilane) (called hereafter PXT) on the structure, mechanical, and dynamic mechanical properties of NR/silica composite were studied. Equilibrium swelling test and scanning electron microscope (SEM) indicate that PXT is able to enhance the crosslinking density of natural rubber (NR)/silica composites and the dispersion of silica in matrix. Mechanical measurement of properties show that PXT can strengthen the reinforcement of silica for NR vulcanizate. In the presence of PXT, the resistance to flex cracking, abrasion and dynamic compression fatigue, and heat build-up of NR/silica composites can be improved substantially. For the application of automotive tire, it also obtains high-skid resistance and low-rolling resistance simultaneously at 2 phr of the PXT concentration. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Effect of PDMS content on waterproofing and mechanical properties of geopolymer composites

The present study mainly studies the effect of polydimethylsiloxane (PDMS) content on the waterproofing and mechanical properties of geopolymer composites. Firstly, hydrophobic modified geopolymer composites (HM-GC) were prepared by adding PDMS during the mixing process. Secondly, the surface wettability characteristics, water absorption, uniaxial compressive and tensile properties of HM-GC were investigated. The effect of PDMS content on the waterproofing and mechanical properties was further discussed. Finally, considering the waterproofing and mechanical properties, the optimal PDMS content was proposed. The results showed that with increasing PDMS content, the contact angle of geopolymer composites rapidly increase at first and then stabilizes. The geopolymer composites with 4% and 5% PDMS content exhibit overhydrophobic surface wettability. In addition, the water absorption gradually decreases with increasing PDMS content, indicating an improvement in the waterproofing ability. The incorporation of PDMS can enhance the compressive properties of geopolymer composites while reducing the tensile properties. Comprehensively considering the waterproofing and mechanical properties, it is reasonable to select 4% as the optimal PDMS content used in practical marine engineering.     

Effect of mica surface treatment on mechanical properties of mica-flake-reinforced cement composites

To determine how the surface modification of mica influences flexural strength and fracture toughness of mica-reinforced cement composites, mica was treated with HF acid and three coupling agents: two silanes (CVBS, γMPS) and a titanate (IDT). Significant increases in mechanical properties resulted, depending on type of treatment, concentration of treating solution, reaction time, and w/c ratio.     

Effect of needle density on the mechanical properties of fiber-reinforced polypropylene composites

The partial impregnation textile preform consisting of chopped-strand, long glass fiber and nonwoven polypropylene (PP) has been prepared by needle-punching to improve fiber–matrix distribution before processing. These unconsolidated textile preforms were then preheated and hot-pressed for consolidation and formation. A multichannel recorder was used to determine the completion of impregnation on multilayer glass fiber-reinforced PP, which could significantly reduce the required consolidation time. The effect of needle density on their impregnation has studied by scanning electron microscopy and optical microscopy, along with mechanical analysis. The increasing needle density up to 400 st/cm² has increased the flexural modulus, but the impact strength decreased. The optimal needle density contained proper flexural and impact properties is 50–100 st/cm², consistent with the observations from scanning electron microscopy and optical microscopy. A similar phenomenon is also observed by using nonwoven maleic-anhydride-modified polypropylene (mPP) instead of unmodified PP. However, the effect of needle punching on flexural and impact properties is not significant in mPP, which is probably due to better adhesion between glass fiber and mPP matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2169–2176, 1999     

Effect of neutron irradiation on the mechanical properties of graphite fiber-based composites

Polymer and carbon composite materials reinforced with K-1100 ultra-high modulus fibers were subject to testing of their radiation resistance. Mechanical tests have been carried out, prior and after neutron irradiation at a dose of 7.1×10¹⁷ n/cm² (E>0.5 MeV) for organic matrix composite and 7.3×10¹⁷ n/cm² (E>0.5 MeV) for carbon matrix composite, to assess the radiation resistance. Flexural strength, deformation at break, Young’s modulus and dimensional changes were measured. Microstructure of the composites before and after irradiation was analyzed. The results showed that neutron irradiation causes significant changes in mechanical properties of composites with organic and carbon matrix and a slight variation in their dimensions. Stronger effects in mechanical properties changes for composites with carbon matrix were observed.     

Effect of organic acids on the mechanical properties of phenolic resin composites

The effect of salicylic acid and its derivatives on the properties of phenolic resin composites was evaluated. The composites were reinforced with aluminum oxide particles in both solid and hollow forms. Differential scanning calorimetry studies have shown that the reaction rate of phenolic resin was accelerated by salicylic acid, but was not affected by the other compounds. Salicylic acid also reduced the flexural strengths of the phenolic resin composites. The strength was decreased by more than 30% in comparison to that with no acid added. In contrast, two derivatives of this acid—sodium salicylate and 4‐hydroxybenzoic acid—have minimal impact on the flexural strengths of the composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 642–647, 2000     

Correlation between physical bonding and mechanical properties of wood plastic composites: Part 1: interaction of chemical and mechanical treatments on physical properties

Abstract

This study investigated the mode of action between wood and thermoplastic interphases. For this purpose, the effect of sanding and chemical treatments on the wood surface wettability has been simultaneously evaluated. Contact angle measurements were tested on wood veneers (spruce) using Van Oss-Chaudhury-Good (VOCG) method to determine the surface free energies (SFE). To better understand the mechanism of treatments on the physical interactions, veneers were either/both sanded or/and treated by maleic anhydride grafted with polyethylene (MAPE) so that the analysis of surface pre-coating and its influence on the polarity and the dispersive properties of the wood-polymer interface can be further studied. The results showed a significant increment of both surface roughness and interfacial area after sanding which improved pre-coating of plastic on the wood surface consequently. Analysis of wetting parameter showed compatibility between two types of surface modification, as the treatment of veneers by sanding and MAPE together resulted in higher contact angles and lower surface free energy (SFE) on the wood surfaces. MAPE could entirely cover the wood veneers and form a non-polar surface, which suggests the effectiveness of this chemical and its compatibility with the sanding operation on the wood surface.     

Filler-elastomer interactions: influence of oxygen plasma treatment on surface and mechanical properties of carbon black/rubber composites

In this work, the influence of oxygen plasma treatment on the surface and adsorption properties of carbon blacks was investigated using X-ray photoelectron spectroscopy (XPS), ζ-potential, and BET isotherms. Then the mechanical properties [tensile strength and tearing energy (G_IIIC)] of carbon black/acrylonitrile butadiene rubber (NBR) composites were measured. As a result, it was found that oxygen plasma treatment generated oxygen-containing functional groups, such as, carboxyl, hydroxyl, lactone, and carbonyl groups, on the carbon black surfaces, resulting in a decrease in the equilibrium spreading pressure or London dispersive component of surface free energy. The tearing energy of the carbon black/NBR composites improved as the oxygen-containing functional groups on the carbon black surfaces increased. This revealed that there is a relatively high degree of interaction between the polar NBR and the oxygen-functional groups of carbon blacks.     

Pultruded fiber-reinforced poly(methyl methacrylate) composites. I. Effect of processing parameters on mechanical properties

A feasibility study of pultrusion of fiber-reinforced thermoplastic PMMA composite has been conducted using a proprietary method. Effect of processing parameters, preparation of methyl methacrylate (MMA) prepolymer on the mechanical properties (tensile, flexural strength and modulus, impact strength, etc.) of fiber-reinforced PMMA composites by pultrusion has been studied. Processing parameters investigated included pulling rate, die temperature, postcure time and temperature, and filler content. From the study of Brookfield viscometer and FTIR spectrum the processing conditions can be defined. It was found from SEM photographs that the wetting out of fibers by PMMA resin was complete, and the fiber bundles were distributed evenly in the PMMA matrix. From the study of ¹H-NMR, GPC, and Brookfield viscometer, the conversion, molecular weight, and viscosity of MMA prepolymer data were obtained. From the DSC diagram, molecular weight measurement, and the rule of polymerization rate, the optimum die temperature was determined. It was found that the mechanical properties increase with increasing filler content and postcure temperature, and with decreasing die temperature and pulling rate.     

Effect of fiber treatment on the mechanical properties of LDPE-henequen cellulosic fiber composites

The degree of mechanical reinforcement that could be obtained by the introduction of henequen cellulosic fibers in a low-density polyethylene, LDPE, matrix was assessed experimentally. Composite materials of LDPE-henequen cellulosic fibers were prepared by mechanical mixing. The concentration of randomly oriented fibers in the composite ranged between 0 and 30% by volume. The tensile strength of these composite materials increased up to 50% compared to that of LDPE. There is also a noticeable increase in Young's modulus for the composite materials that compares favorably with that of LDPE. As expected, the addition of the fibers decreases the ultimate strain values for the composite materials. The thermal behavior of the LDPE-henequen cellulosic fibers materials, studied by differential scanning calorimetry, DSC, showed that the presence of the fibers does not affect the thermal behavior of the LDPE matrix; thus, the interaction between fiber and matrix is probably not very intimate. Preimpregnation of the cellulosic fibers in a LDPE-xylene solution and the use of a silane coupling agent results in a small increment in the mechanical properties of the composites, which is attributed to an improvement in the interface between the fibers and the matrix. The shear properties of the composites also increased with increasing fiber content and fiber surface treatment. It was also noted that the fiber surface treatment improves fiber dispersion in the matrix. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 197–207, 1997     

Novel,low-cost jute-polyester composites. Part 1: Processing,mechanical properties,and SEM analysis

The development of high performance composites from a cheap natural fiber, jute, as reinforcement is particularly significant from an economic point of view. In this work, jute fiber-unsaturated polyester(GP) composites having appreciable mechanical properties were prepared by using solution impregnation and hot curing methods. Both unbleached (control) and bleached jute slivers with various percentages of fiber loadings were used to prepare the composites and were named JPH (C) i.e., Jute Polyester Hot Curing (control), and JPH (B) i.e., Jute Polyester Hot Curing (bleached), respectively. Mechanical properties such as tensile and flexural strain, toughness, and moduli of both the grades have been compared. Composites having 60 wt% of jute fiber yielded the best results. JPH (B) showed much better flexural properties than JPH (C), although the tensile properties of the latter were better. The inter-laminar shear strength (ILSS) of the JPH (B) was found to be higher than JPH (C). The nature of fiber-resin bonding was studied from scanning electron micrographs of the specimens subjected to tensile and flexural fracture. Dynamic mechanical properties were found to be very high, superior even to those of glass fiber reinforced composites. The flexural storage modulus was found to be 12.3 GPa at 30°C and to decrease slowly with temperature. The major finding in this work is the attainment of high mechanical properties of composite specimens with 60 wt %fiber loading. On a weight and cost basis, bleached jute fibres were found to be better reinforcements than other fibers with usual surface modification by coating or grafting processes.     

Effect of fluoride additive on the mechanical properties of hydroxyapatite/alumina composites

The effect of fluoride additives on the mechanical properties of hydroxyapatite/alumina composites was investigated. When MgF₂ (5 vol%) was added to hydroxyapatite/alumina composites, the decomposition of hydroxyapatite was suppressed due to the substitution of F⁻ for OH⁻ in the crystal structure. Comparing two additives, such as MgF₂ and CaF₂, MgF₂ showed much more effective for the suppression of phase decomposition in the hydroxyapatite/alumina composites due to the enhanced substitution of F⁻ for OH⁻. In the case of MgF₂ addition, a relatively high-mechanical properties (flexural strength: ∼170 MPa; Vickers hardness: ∼7 GPa) was obtained compared to MgF₂-free composites.     

Effect of filler partitioning on the mechanical properties of TPO/nanosilica composites

Nanosilica (SiO₂) is used as a reinforcing filler in PP/elastomer thermoplastic polyolefin (TPO) blends containing ethylene‐octene polyolefin elastomer (POE), ethylene‐propylene rubber (EPR), and maleated EPR. The localization and dispersion of the filler are controlled by adding maleated derivatives to the matrix or the dispersed phase. A separated morphology, consisting of SiO₂ residing in the PP matrix, is necessary to achieve improvements in modulus. Filled TPOs containing POE have the best performance and exhibit improved moduli while retaining high values of elongation. J. VINYL ADDIT. TECHNOL., 13:147–150, 2007. © 2007 Society of Plastics Engineers     

Effect of polyethylene glycol on mechanical properties of bamboo fiber-reinforced polylactic acid composites

The bamboo fiber (BF)-reinforced polylactic acid (PLA) composites were prepared using the twin-screw extruder and injection molding. Thermal gravimetric analyzer results indicated the thermal stability of BF/PLA composites decreased with increasing BF content. Differential scanning calorimeter and X-ray diffraction curves showed that BF played a role as a nucleating agent, but the crystallinity of composite materials decreased with the increasing BF content. The melt flow rate of composites reduced with the increase in BF content, resulting in a poorer processing property. The processability of the composites was improved with the addition of high molecular polyethylene glycol (PEG). Mechanics performance test showed that tensile strength and bending strength of composites increased at low loading with the BF content increased then decreased when the loading continued to increase. The tensile strength of the composite materials reached 65.46 MPa when alkali-treated BF (ABF) content was 20 wt %. The flexural strength of the composites reached 97.94 MPa when ABF content was 10 wt %. Impact performance has also been improved. PEG-20000 was the best plasticizer among the PEG-6000,PEG-10000, and PEG-20000. When the component of PEG was 10 wt %, the elongation increased by 56%. The scanning electron microscopy (SEM) result showed that the fracture of the composites was smooth, most ABF were wrapped in matrix and distribution of ABF in PLA matrix was more uniform. It means that interfacial compatibility of bamboo fiber and PLA improved after BF modified by alkali. High molecular weight PEG enhance melt flow ability of polymer, result in fibers were further enclosed in the PLA matrix and increase properties of composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47709.     

Effect of the talc filler content on the mechanical properties of polypropylene composites

This research examines the effect of a microsize/nanosize talc filler on the physicochemical and mechanical properties of filled polypropylene (108MF10 and 33MBTU from Saudi Basic Industries Corp. and HE125MO grade from Borealis) composite matrices. A range of mechanical properties were measured [tensile properties, bending properties, fracture toughness, notched impact strength (at the ambient temperature and ?20°C), strain at break, and impact strength] along with microhardness testing and thermal stability testing from 40 to 600°C as measured by differential thermal analysis and thermogravimetric analysis. Increasing filler content lead to an increase in the mechanical strength of the composite material with a simultaneous decrease in the fracture toughness. The observed increase in tensile strength ranged from 15 to 25% (the maximum tensile strength at break was found to be 22 MPa). The increase in mechanical strength simultaneously led to a higher brittleness, which was reflected in a decrease in the mean impact strength from the initial 18 kJ/m² (for the virgin polypropylene sample) to 14 kJ/m², that is, a 23% decrease. A similar dependency was also obtained for the samples conditioned at ?20°C (a decrease of 12.5%). With increasing degree of filling of the talc–polypropylene composite matrix, the thermooxidative stability increased; the highest magnitude was obtained for the 20 wt % sample (decomposition temperature = 482°C, cf. 392°C for the virgin polymer). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008