Studies on interfacial adhesion in unidirectional isora fibre reinforced polyester composites

Unidirectional isora fibre reinforced polyester composites were prepared by compression moulding. Isora is a natural bast fibre separated from the Helicteres isora plant by a retting process. The effect of alkali treatment on the thermal properties of the fibre was studied using TGA, DTA and DSC in oxygen and nitrogen atmosphere. Mechanical properties like tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali-treated fibres have been studied as a function of fibre loading. The optimum loading for tensile properties of the composite containing untreated fibre was found to be 45% by volume and on alkalization of the fibre, the optimum loading increased to 66%. For flexural properties the loading was optimized at about 56% and 66%, for the composites containing untreated and alkali treated fibres, respectively. From DMA studies it was observed that the alkali-treated fibre composites have higher E′ and E″ values compared to untreated fibre composites. From swelling studies in styrene it was observed that the mole percent uptake of the solvent by the treated fibre composites is less than by the untreated fibre composites. From these results it can be concluded that in composites containing alkalized fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Mechanical Properties and Morphology of Polylactide Composites with Acrylic Impact Modifier

Polylactide (PLA) composites with acrylic impact modifier BPM, i.e., PLA/BPM composites, were produced by the melt blending method. The effects of BPM on the thermal properties, melting behaviors, and dynamic mechanical properties of the PLA/BPMs were investigated by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Tensile strength, flexural strength, and modulus of the injection molded specimens were measured by an Instron tensile machine. The influence of BPM on the impact strength of injection molded PLA/BPM composites was examined using an impact tester. The morphology of cryofractured surfaces and fracture surfaces of the composites after the tensile and impact testing was also investigated using scanning electron microscope. The test results show that the composites with BPM possess better flexibility when compared with neat PLA. However, the notched Izod impact strength showed improvement only when the BPM content was higher than 15 wt%.     

Mechanical and Thermal Properties Enhancement of Poly(Lactic Acid)/Halloysite Nanocomposites by Maleic-Anhydride Functionalized Rubber

Poly(lactic acid) (PLA)/halloysite composites were prepared using melt compounding followed by compression molding. Maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH) was used to toughen the PLA composites. The mechanical properties of the PLA composites were studied through tensile, flexural, and impact tests. The thermal properties were characterized by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The fracture surfaces of the composites were assessed by using field emission scanning electron microscopy (FESEM). The impact strength and thermal properties of the PLA/halloysite composites were increased by addition of SEBS-g-MAH.     

Filler treatment effects on the weathering of talc-, CaCO3- and kaolin-filled polypropylene hybrid composites

Talc, calcium carbonate (CaCO₃), and kaolin hold considerable promise in the development of polymer composites for good mechanical properties and stability. Comparative studies on the usage of these minerals as single fillers in polypropylene (PP) have shown varying degrees of reinforcement due to their differences in terms of particle geometry, surface energy and affinity towards the matrix polymer. In this study, comparisons were made in terms of mechanical, thermal and weatherability properties between hybrid-filler PP composites (i.e. PP filled with either talc–CaCO₃ or talc–kaolin hybrid filler combinations), with particular attention directed towards the effect of surface modification of the fillers. The talc/CaCO₃ hybrid composites have shown exceptional performance in terms of flexural and impact properties. The contribution of talc in the talc–kaolin hybrid composite system has been significant in terms of enhancing the overall tensile and flexural properties. The ability of silane and titanate coupling agents in boosting the resistance of the composites to severe damage and degradation due to natural weathering has been shown.     

Effect of Surfactant Concentration on Thermal and Mechanical Properties of Poly(Butylene Succinate)/Organoclay Composites

Composite materials consisting of poly(butylene succinate) (PBS) and montmorillonite (MMT), modified to various extents using trihexyltetradecylphosphonium chloride (THTDP) cations, were prepared using a simple melt intercalation technique. The surfactant contents were varied, i.e. 0.4, 0.6, 0.8, 1.0, and 1.2 times the cation exchange capacity (CEC) of the MMT. The intercalation of the surfactant molecules into MMT layers, confirmed by the increase in interlayer spacing and significant changes in the morphology of the modified MMT, facilitated the dispersion of the clay in the PBS matrix. The properties of the PBS-based composites were changed with increasing surfactant content. The melting and crystallization temperatures increased and the degree of crystallinity (χ_c) decreased. The storage modulus was significantly enhanced below the glass transition temperature (Tg), and Tg shifted to a higher temperature, with a maximum at a surfactant loading of 0.6 CEC. The mechanical properties, including tensile strength, flexural strength, flexural modulus and impact strength, increased and then decreased with surfactant loading, with the maximum observed also at a surfactant loading of 0.6 CEC. In conclusion, an ideal balance between thermal and mechanical properties can be obtained at a surfactant quantity equivalent to 0.6 times the clay CEC. Moreover, all the composites exhibited obvious improvement in thermal and mechanical properties as compared to those of neat PBS.     

Mechanical and tribological enhancement of polyoxymethylene-based composites with long basalt fiber through melt pultrusion

Abstract

The polyoxymethylene (POM)/basalt fiber composites were prepared by use of long fiber-reinforced thermoplastic technology through melt pultrusion. The mechanical and tribological properties, morphology, and thermal stability of the resulting composites were investigated. The composites exhibit significant improvements in tensile, flexural, and notched impact strength. These mechanical strength and toughness are dependent on the fiber content over the full range of the study. The residual fiber length and distribution in the injection-molded specimens were characterized. The prominent reinforcement effect of basalt fiber on POM is derived from the supercritical fiber length, which is much longer than that of the short fiber-reinforced ones and thus makes the composites take full advantage of the strength of the reinforcing fibers. The Kelly–Tyson model was used to predict the ultimate tensile strength of POM composites using the measured values of residual fiber length in the matrix, but the deviations were observed at the high contents of basalt fiber. The morphologic investigation indicates that the fiber pullout and fiber breakage both contribute energy dissipation to the tensile fracture of the composites. The tribological characterization indicates that the friction coefficients and specific wear rates of POM composites also decrease remarkably. Such an improvement of tribological performance is due to the presence of the high wear-resistant basalt fibers on the top of the worn surface bearing the dynamic loadings under sliding. Moreover, the dynamic mechanical analysis reveals that the storage moduli of the composites increase with increasing the fiber content, whereas the loss factors present an opposite trend.     

Optimizing mechanical and thermal expansion properties of carbon/carbon composites by controlling textures

The present study explored the effect of medium texture (MT) content on flexural properties and thermal expansion coefficients (CTE_S) of carbon/carbon (C/C) composites with multilayered pyrolytic carbon. The specimen with 39% MT exhibited maximum flexural strength of 221.55 MPa, increasing by 52% compared with pure high texture. While the flexural strength decreased when the MT content exceeded 39%. The excellent strength can be attributed to crack deflection between multilayered texture and the strong interface bonding between fibers and matrix. Moreover, the four specimens expressed a similar trend of CTE_S in the direction of XY and Z. In the direction of XY, the specimen with 39% MT had the lowest CTE_S from 800 °C to 2100 °C. Therefore, the C/C composites with 39% MT have the best mechanical and thermal expansion properties, which means that the properties of C/C composites can be optimized by controlling the texture.     

Physical Properties of Micro Hollow Glass Bead Filled Castor Oil-Based Polyurethane/Epoxy Resin IPN Composites

A series of micro hollow glass beads (HGB) filled castor oil-based polyurethane/epoxy resin graft interpenetrating polymer network (IPN) composites were prepared. The tensile and impact strengths, impact fractured surfaces, damping properties and thermal stability of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of HGB into polyurethane/epoxy IPN can significantly improve not only the tensile strength but also the impact strength. The tensile strength was increased by 61% and at the same time the impact strength was increased by 25% when the HGB content was 1.5%. The damping properties were better than the composition of 0.5% or 2% HGB content when the HGB content was 1% or 1.5%. The thermal decomposition temperature was also slightly improved by the incorporation of HGB. It is suggested that the HGB reinforced polyurethane/epoxy resin IPN composites could be used as structural damping materials.     

Effect of Carbon Nanotubes on the Mechanical Properties of Polypropylene/Wood Flour Composites: Reinforcement Mechanism

Maleic anhydride grafted polypropylene (PP-g-MA) was employed as the compatibilizer and carbon nanotubes (CNTs) or hydroxylated CNTs as reinforcements for polypropylene/wood flour composites. The results showed that when the PP-g-MA loading level was 10 wt%, the bending strength, tensile strength, Izod notched impact strength, and elongation at break of PP-wood composites were enhanced by 85% (66.3 MPa), 93% (33.7 MPa), 5.8% (2.01 kJ/m²), and 64% (23%), respectively, relative to the uncompatibilized composites. The introduction of pristine CNTs only improved slightly the overall mechanical properties of the compatibilized composites due to poor interfacial compatibility. Unlike CNTs, incorporating hydroxylated CNTs (CNT-OH) could significantly improve all of the mechanical properties; for instance, at 0.5 wt% CNT-OH loading, the flexural strength and tensile strength reached 68.5 MPa, and 40.4 MPa about 6.6% higher than that for the composites with the same CNT loading. Furthermore, CNT-OH also remarkably enhanced the storage modulus. Contact angle and morphology observations indicated that the increases in mechanical properties could be attributed to the improvements of interfacial interactions and adhesions of CNTs with the matrix and fillers.     

Mechanical and electrical properties of radiation-vulcanized natural rubber latex with waste eggshell powder as bio-fillers

ABSTRACT

This work investigated the mechanical, physical, morphological, and electrical (volume) resistivity properties of radiation-vulcanized natural rubber latex (RVNRL) with additions of waste eggshell (WES) powder, which contained primarily CaCO₃ (calcite). The results showed that increasing gamma irradiation doses from 0 to 30?kGy in 10-kGy increments led to decreases in the swelling ratio and elongation at break but increases in the crosslink density, tensile modulus at 500% elongation, and tensile strength of the composites. The results also suggested that increasing the WES contents from 0 to 2, 4, or 6 parts per hundred parts of rubber by weight (phr) in the composites improved the tensile modulus at 500% elongation, tensile strength, hardness (Shore A), and electrical (volume) resistivity. In addition, after undergoing thermal aging at 70°C for 96?h, the tensile modulus and hardness (Shore A) increased, while the tensile strength and elongation at break decreased. This work also compared the properties of WES/RVNRL with commercial CaCO₃/RVNRL samples at the same 4-phr content. The results indicated that both composites had similar tensile properties, implying possible replacement of commercial CaCO₃ with WES powder as an effective reinforcing filler in RVNRL.     

Flexural Properties of Poly-L-Lactide and Polycaprolactone Shape Memory Composites Filled with Nanometer Calcium Carbonate

The flexural properties of poly-L-lactide (PLLA) and polycaprolactone (PCL) shape memory composites filled with nanometer calcium carbonate (nano-CaCO₃) were determined at room temperature. The results showed that with the increase of the nano-CaCO₃ weight fraction the flexural moduli and strength of PCL/nano-CaCO₃ composites increased roughly linearly and reached a maximum at the filler content of 2%, while the flexural strength of the composites decreased. The flexural moduli and strength of the composites decreased roughly linearly with increasing PLLA/PCL ratio for the PLLA/PCL/nano-CaCO₃ composites.     

Effect of Surface Structure of Nano-CaCO3 Particles on Mechanical and Rheological Properties of PVC Composites

To study the effect of different surface structures on resultant mechanical and rheological properties, nano-CaCO₃ particles were treated with isopropyl tri-stearyl titanate (H928), isopropyl tri-(dodecylbenz-enesulfonyl) titanate (JN198), and isopropyl tri-(dioctylpyrophosphato) titanate (JN114). Scanning electron microscopy (SEM) and dynamic mechanic analysis (DMA), carried out to characterize the effective interfacial interaction between the nano-CaCO₃ particles and a poly(vinyl chloride) (PVC) matrix, indicated that JN114 treated nano-CaCO₃ particles had the strongest interfacial interaction with a PVC matrix, while H928 treated nano-CaCO₃ had the weakest. The rheological and mechanical properties of PVC/nano-CaCO₃ composites were investigated as a function of surface structure and filler volume fraction. The tensile yield stress and elongation at break decreased with the increasing of calcium carbonate content while tensile modulus increased. PVC filled with JN114 treated nano-CaCO₃ had the highest tensile modulus and tensile yield stress, while those filled with H928 treated nano-CaCO₃ had the highest elongation at break at the same filler content. The impact strength of PVC/nano-CaCO₃ composites increased with the increasing of CaCO₃ content, and PVC composites filled with JN198 treated nano-CaCO₃ particle had a higher impact strength than those with JN114 or H928 treated, with the value reaching 23.9 ± 0.7 kJ/m² at 11 vol% CaCO₃, four times as high as that of pure PVC. Rheological properties indicated that a suitable interfacial interaction and a good dispersion of inorganic filler in a PVC matrix could reduce the viscosity of PVC/nano-CaCO₃ composites. The interfacial interaction was quantitatively characterized by semiempirical parameters calculated from the tensile strength of PVC/nano-CaCO₃ composites to confirm the results from the SEM and DMA experiments.     

Effect of Modified Intumescent Flame Retardant via Surfactant/Polyacrylate Latex on Properties of Intumescent Flame Retardant ABS Composites

In order to prepare intumescent flame retardant acrylonitrile-butadiene-styrene (ABS) composites with only a small decrease in their mechanical properties, we investigated the effect of adding an elastomeric polyacrylate latex and the surfactant TX-10 phosphate to modify the ammonium polyphosphate, melamine, and calcium 3-hydroxy-2, 2-bis(hydroxymethyl) propyl phosphate normally used, which resulted in an intumescent flame retardant composite (IFRC) powder with the aim of improving compatibility. These ABS/IFRC composites were compared with standard material containing unmodified intumescent flame retardant (NIFR) by investigating their thermal properties, melt characteristics, mechanical properties, and microstructure. The data showed that the glass transition temperature of the ABS/IFRC composites decreased slightly in all cases, the complex viscosity of the ABS/IFRC composites was remarkably reduced, and the mechanical properties improved in comparison with the material containing NIFR. A slight increase in impact strength retention, as well as a remarkable increase in tensile and flexural strength retention of ABS/IFRC, was achieved due to superior compatibility between ABS and IFRC in comparison with ABS/NIFR.     

Mechanical Properties Comparison of Various Ratios of L-Lactide Grafted Sisal Fibers and Untreated Sisal Fibers Reinforced Poly (lactic acid) Composites

Composites composed of the mixed fibers of L-lactide (LA) grafted sisal fiber (SF-g-LA) and untreated sisal fiber (USF) in a poly (lactic acid) (PLA) matrix were prepared with SF-g-LA/USF fibers ratios of 0, 1:9, 3:7, 5:5, 7:3, 9:1, and 1. The mechanical properties and the interfacial performance of the mixed SF reinforced PLA composites were investigated. The results of the study showed that the introduction of SF-g-LA improved the tensile strength, tensile modulus, flexural strength and flexural modulus of the mixed SF reinforced PLA composites compared with pure PLA or PLA composites with only USF, resulting from the improved interfacial adhesion between SF-g-LA and the PLA matrix. In addition, the introduction of some amount of USF enhanced the reinforcing efficiency of the mixed SF in the composites compared to the PLA composites with only SF-g-LA, owing to the good mechanical properties of USF itself. Furthermore, as for the tensile strength and tensile modulus of the mixed SF reinforced PLA composites, the optimal ratio of SF-g-LA and USF was 7:3, whereas for the flexural modulus of the mixed SF reinforced PLA composites, the optimal mixed ratio of SF-g-LA and USF was 3:7.     

Evaluation of thermomechanical properties of epoxy–basalt fibre composites modified with zeolite and silsesquioxane

The aim of this study was to verify the influence of zeolite and silsesquioxane (POSS) addition on thermo-mechanical properties of basalt fiber reinforced epoxy composites. The dynamic mechanical thermal analysis was conducted with different frequencies at bending mode. The mechanical properties were determined at static tensile test and Charpy impact strength method. The structure of composites was determined by scanning electron microscopy. The thermal stability was characterized by thermogravimetric analyses in inert and oxidizing atmospheres. The impact strength and thermal stability of the composites with zeolite and silseqioxane were higher than the reference sample. Thus, these composites can be used as thermally stable materials with high stiffness.     

Morphology,mechanical, rheological,and thermal properties study on the PTT/ABS/SCF composites

In order to improve the mechanical properties of the poly(trimethylene terephthalate) (PTT), both maleinized acrylonitrile–butadiene–styrene (ABS) and short carbon fiber (SCF) were melt-blended with PTT to prepare the composites and their morphology and properties were investigated in detail. When ABS content is fixed at 5?wt.% in composites, SCF can significantly improve the tensile and flexural strength as well as the impact strength of the matrix. The SCF has good interface adherence with the matrix. At glassy state, the storage modulus increases much with increasing SCF content. At rubbery state, the composites have larger cold-crystallization rate. At molten state, SCF first serves as lubricants and then as viscosity reinforcing agent for the matrix with increasing SCF. The composites melt exhibits increasing elastic behaviors with SCF. The composites have larger crystallization rate, but this accelerating effect decreases with excessive SCF content. The crystals formed in different composites are quite different in size or perfection.     

Studies on short isora fibre-reinforced polyester composites

This paper reports the use of a natural fibre, isora, as reinforcement in unsaturated polyester resin. Isora is a bast fibre separated from the bark of Helicteres isora plant by retting process. Properties like tensile strength, flexural strength etc. have been studied as a function of fibre length and fibre loading using treated and untreated fibre. The mechanical properties were found to be optimum at a fibre length of 30 mm and a fibre loading of 30% by volume. The effects of alkali treatment on the fibre properties were investigated by SEM, IR and TGA. The mechanical performance of the treated isora fibre-reinforced polyester composites has also been investigated. SEM studies were carried out to investigate the fibre surface morphology, fibre pull-out and fibre–polyester interface bonding. SEM gave evidence for the changes that had occurred on the fibre surface during chemical treatment. The properties were found to be superior for the composite reinforced with treated fibre compared to the untreated fibre.     

Influence of SiC Electron Acceptor–Donor Modification on Thermal and Physical Properties of Carbon Fiber/SiC/Epoxy Composites

In this work, the effects of electron acceptor–donor modification on the surface properties of SiC were investigated in the mechanical interfacial properties of carbon fibers-reinforced SiC-impregnated epoxy matrix composites. The surface properties of the SiC were determined according to acid/base values and FT-IR, and contact angle measurements. The thermal and mechanical interfacial properties of the composites were evaluated using a thermogravimetric analysis, critical strain energy release rate mode II (G _IIC), and impact strength testing. As a result, the electron acceptor-treated SiC had a higher acid value and polar component in surface free energy than did the untreated SiC or the electron donor-treated SiC. The G _IIC and impact strength mechanical interfacial properties of the composites had been improved in the specimens treated by acidic solutions due to the good wetting and a high degree of adhesion with electron donor characteristic epoxy resins.     

Calcium Sulfate as High-Performance Filler for Polylactide (PLA) or How to Recycle Gypsum as By-product of Lactic Acid Fermentation Process

Reinforcing of polylactide (PLA) with fillers can be an interesting solution to reduce its global price and to improve specific properties. Starting from calcium sulfate (gypsum) as by-product of the lactic acid fermentation process, novel high performance composites have been produced by melt-blending PLA and this filler after a previous specific dehydration performed at 500°C for min. 1 h. 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 hemihydrate is a prerequisite. Then, the modification of filler interfacial properties with different coating agents such as stearic acid (SA) and stearate salts has been considered. The effect of surface treatment on molecular, thermal and mechanical properties has been examined together with the morphology of the resulting composites. To take advantage of the improved lubricity and better wetting characteristics, the filler was coated by up to 2% (by weight) SA. The coating of the filler leads to PLA–AII composites that surprisingly exhibit thermal stability, cold crystallization and enhanced impact properties. Such remarkable performances can be accounted for by the good filler dispersion as evidenced by SEM–BSE imaging of fractured surfaces. As far as tensile proprieties are concerned, notable utilization of uncoated filler or filler coated by stearate salts leads to PLA–AII composites characterized by higher tensile strength and Young's modulus values. The study represents a new approach in formulating new melt-processable grades with improved characteristic features by using PLA as polymer matrix.     

Effect of Fiber Surface Modification on the Interfacial and Mechanical Properties of Kenaf Fiber-Reinforced Thermoplastic and Thermosetting Polymer Composites

The surfaces of kenaf fibers were treated with three different silane coupling agents. 3-glycidoxypropyltrimethoxy silane (GPS), 3-aminopropyltriethoxy silane (APS), and 3-methacryloxypropyltrimethoxy silane (MPS). Among them, the most effective one for the property improvement was GPS when it was applied to the kenaf fiber surfaces at 0.5 wt%. Thermoplastic polypropylene (PP) and thermosetting unsaturated polyester (UPE) matrix composites with chopped kenaf fibers untreated and treated at different GPS concentrations from 0.1 wt% to 5 wt% were fabricated using compression molding technique. The present study demonstrates that the interfacial, flexural, tensile, and dynamic mechanical properties of both kenaf/PP and kenaf/UPE composites importantly depend on the GPS treatments done at different concentrations. The greatest property improvement of both thermoplastic and thermosetting polymer composites was obtained with the silane treatment at 0.5 wt% and the mechanical properties were comparable with E-glass composites prepared the same polymer matrix under the corresponding fiber length and fiber loading. The results also agreed with each other with regard to their interfacial shear strength, flexural properties, tensile properties, storage modulus, with support of fracture surfaces of the composites.