The role of interface modification on the mechanical properties of injection-moulded composites from commingled polypropylene/banana granules

Commingled polypropylene (PP)/banana granules were fabricated from slivers by mixing PP fibers and banana fibers by textile equipment. By twisting the sliver, the reinforcing fibers were compacted and bonded with the molten matrix material. PP/banana composites were prepared from commingled PP/banana granules by injection moulding method with special reference to the effect of maleic anhydride modified polypropylene (MAH-PP) concentration. The mechanical properties of the composites were found to depend on the concentration of MAH-PP. The tensile and flexural properties of the composites increased with the addition of MAH-PP up to 2 wt%. After 2 wt% addition of MAH-PP, these properties tend to be stabilized. On the other hand the unmodified composites showed the maximum impact strength. Fourier transform infrared spectroscopic (FTIR) analysis of the MAH-PP modified composites showed evidence of a chemical bridge between the hydroxyl group of the banana fiber and maleic anhydride of the MAH-PP through an esterification reaction. The feature peak of the esterification occurred in the range ～ 1743 cm^?1. In order to confirm the esterfication reaction further, FTIR spectra of the banana microfibrils and MAH-PP modified PP/banana microfibril composites were taken and compared. The tensile fracture surfaces of the unmodified and MAH-PP modified PP/banana composites were studied by scanning electron microscopy (SEM). An improvement in adhesion between the fiber and the matrix was observed in the case of MAH-PP modified composites. Two different processing methods, both injection and compression mouldings were performed to prepare the PP/banana composites. Tensile properties of the composites prepared by these two methods were compared. The enhancement of tensile properties for injection-moulded composites compared to the compression-moulded composites is owing to the occurrence of orientation, better mixing and interaction between the fiber and the matrix during injection moulding. Finally, experimental results of the tensile properties of the injection-moulded composites have been compared with theoretical predictions.     

Assessment of dicumyl peroxide ability to improve adhesion between polylactide and flax or hemp fibres

Dicumyl peroxide (DCP) is commonly applied as a cross-linking agent in polymer processing. The main aim of this work was to assess the ability of DCP to improve adhesion between polylactide (PLA) and flax or hemp fibres by their interphase cross-linking. Short fibre-reinforced PLA composites were manufactured due to the importance of short fibres in injection moulding of high-quality biocomposites. Reactive extrusion of the PLA, flax or hemp fibres, and DCP was performed. The flax or hemp fibre content was 10?wt%, while DCP varied with 0.5 and 2.5?wt%. The fibres and PLA were mechanically mixed, extruded, granulated and injection moulded to form samples for testing. The samples were characterized by differential scanning calorimetry (DSC), tensile and impact strength tests, dynamic mechanical analysis and scanning electron microscopy (SEM). It was found that flax and hemp fibres increased the Young’s modulus while these fibres decreased the impact strength. Addition of DCP led to increase in PLA crystallinity at the interface with fibres which led to further decrease in impact strength. For that reason, it was concluded that DCP is an ineffective agent to improve interphase adhesion between PLA and short flax or hemp fibres.     

Surface Modification of Ultrahigh-molecular-weight Polyethylene Fibers with Coupling Agent during Extraction Process

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated with a coupling agent following the extraction of gel fibers, resulting in modified fibers after subsequent ultra-drawing. The structure and morphology of the modified UHMWPE fibers were characterized and their surface wetting, interfacial adhesion, and mechanical properties were investigated. It was found that the coupling agent was absorbed into the UHMWPE fiber and trapped on the fiber surface. Compared with unmodified UHMWPE fibers, the modified fibers had smaller contact angle, higher crystallinity, and smaller crystal size. The interfacial adhesion and mechanical properties of UHMWPE fibers were significantly improved with increasing coupling agent concentration and gradually reached a plateau value. After treatment with 1.5 wt% solution of a silane coupling agent (γ -aminopropyl triethoxysilane, SCA-KH-550), the interfacial shear strength of the UHMWPE-fiber/epoxy composites was increased by 108% and the tensile strength and modulus of modified UHMWPE fibers were increased by 11% and 37% respectively.     

Improving the interfacial strength of PMMA resin composites by chemically grafting graphene oxide on UHMWPE fiber

Controlling interfacial microstructure and interactions between (ultra high molecular weight polyethylene) UHMWPE fiber and matrix is of crucial importance for the fabrication of advanced polymer composites. In this paper, (UHMWPE fiber-g-graphene oxide [GO]) was prepared. GO nanoparticles distributed onto the ?ber surface uniformly, which could increase surface polarity and roughness. Increases of interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of UHMWPE fiber-g-GO composites were achieved. These enhancements can be attributed to the existent of GO interface with providing chemical bonding and strong mechanical interlocking between the ?ber and matrix. Moreover, impact resistance of UHMWPE fiber-g-GO composites was enhanced.     

Powder compaction,sintering, and rolling of ultra high molecular weight polyethylene and its composites

The applicability of powder compaction and sintering techniques to the processing of ultra high molecular weight polyethylene (UHMWPE) powder is demonstrated. With proper processing procedure and type of UHMWPE powder, the mechanical properties obtained are nearly equivalent to those obtained by conventional melt processes. The properties were optimized by selection of a sintering temperature just above the melting point and by close control of particle size and distribution. The processability of UHMWPE is dependent on the morphology of the powder. Only those powders with a fibrous morphology provided good mechanical properties after sintering. The mechanical properties of powder compacts can be improved by several techniques. Liquid sintering with added normal molecular weight polyethylene, with close control of particle size and distribution and amount of the second component, yielded improved properties. Composites of UHMWPE, with short glass and graphite fiber reinforcement, processed by powder compaction and sintering resulted in increased modulus. The properties of these composites depended upon the amount of fibers, fiber length, fiber-matrix bonding, and fiber orientation. Rolling the powder-processed UHMWPE oriented the structure and improved the mechanical properties, although it decreased the mechanical properties of the glass and graphite fiber composites because of debonding between fiber and matrix. The properties of carbon black—UHMWPE mixtures were improved by rolling because of a more uniform distribution of carbon black.     

Mechanical and dielectric properties of SEBS modified by graphite inclusion and composite interface

Tough and flexible dielectrics were prepared using graphite (G), a natural and low-cost resource, as filler in polystyrene-b-(ethylene-co-butylene)-b-polystyrene (SEBS) and maleinized SEBS (SEBS-MA) matrices. The disintegration of graphite in submicron particles was accomplished by the shear forces during the melt processing step and it was highlighted by atomic force microscopy. Simultaneous increase of tensile strain, strength and Young's modulus was noticed for SEBS/G and SEBS-MA/G composites compared to unfilled matrices, this remarkable feature being previously reported only for some nanocomposites. Moreover, an exponential variation of the dielectric permittivity with the volume fraction of G was obtained. Higher reinforcing efficiency and better dielectric properties were observed in SEBS-MA/G composites, compared to the corresponding SEBS/G composites, due to the stronger polymer–filler interface and better dispersion of graphite. This study brings new insights into nanolevel properties of SEBS composites and it opens new perspectives on high performance composites by using graphite instead of expensive graphene and efficient melt mixing process.     

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%.     

Influence of Carbon Nanotubes on the Crystallization and Directional Tensile Behavior of High-Density Polyethylene Prepared by Dynamic-Packing Injection Molding

The influence of multi-walled carbon nanotubes (MWCNTs) on the crystallization and directional tensile properties of high-density polyethylene (HDPE) was studied for samples prepared by dynamic-packing injection molding (DPIM). Oscillatory shear was imposed on the gradually cooled melt during the packing solidification stage of DPIM. For the oriented composites containing 1.8 wt% MWCNTs, the tensile fracture behavior showed typical brittle features along the flow direction (FD) and perpendicular direction (PD), which were almost the same as those that occurred in oriented pure HDPE. The elongation at break along both directions decreased due to the incorporation of MWNCTs in the oriented composites compared with the oriented pure HDPE. However, the tensile strength of the oriented HDPE/MWCNT composites was greatly improved along the FD due to the presence of carbon nanotubes; meanwhile, it was not weakened along the PD. In scanning electron microscopy observations, it was found that there were some oriented hybrid shish-kebab structures in a nanometre scale in the oriented HDPE/MWCNT composites, but not in its isotropic composites. This suggests that MWCNTs were involved in the shear-induced crystallization of HDPE. Differential scanning calorimetry measurements confirmed that the crystallinity of oriented HDPE composites with 1.8 wt% MWCNTs was higher than those of isotropic HDPE and isotropic composites, but was not obviously higher than that of oriented pure HDPE. These findings demonstrate that MWCNTs indeed affected the formation of crystalline structures, but did not greatly influence the crystallinity of HDPE under shear flow. The transition of crystalline morphology might be the reason for change in tensile behavior for the oriented HDPE/MWCNT composites compared with the oriented pure HDPE.     

Ultrasonic moulding of plastic powders

Polypropylene powder has been moulded by the application of ultrasonic vibrations and attempts have been made to optimize the strength of the mouldings. The most important variables are the duration of the ultrasonic vibrations and the subsequent dwell time during which the pressure is maintained. It was also found that the smaller the particle size of the powder the greater was the tensile strength of the mouldings. The compaction pressure did not have any significant effect on strength.Under the best conditions a tensile strength of 20 MPa was recorded, which is about 85% of the value achieved by injection moulding. However, the ductility of the mouldings was always considerable less than that which would normally be expected from polypropylene.     

Nanoporous Nanocomposite Hydrogels Composed of Polyvinyl Alcohol and Na-montmorillonite

Polyvinyl alcohol nanoporous nanocomposite hydrogels containing various levels of Na-montmorillonite were prepared by a cyclic freezing–thawing technique. An exfoliated morphology of silicate layers was observed for the nanocomposite hydrogels. The uniaxial tensile test indicated that the tensile modulus and tensile strength of the nanocomposite hydrogels increased with increasing Na-montmorillonite content, while their elongation-at-break values decreased. The results showed that by adding 15 wt% of montmorillonite to polyvinyl alcohol hydrogels, the molecular weight of polymer chains between two adjacent cross-links decreased to 56% and the effective cross-linking density increased up to 353%. It is also indicated that all nanocomposite hydrogel samples had nanoscale pore diameters and network mesh sizes less than 30 nm. The nanoporous structure of the nanocomposite hydrogels was confirmed by transmission electron microscopy observations and mercury intrusion porosimetry tests.     

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.     

Effect of Amphiphilic Polymer Modified Graphene Surfactant on the Thermal,Viscoelastic and Tensile Properties of Nitrile Latex Nanocomposites

Carboxylated butadiene-nitrile latex (CBNL) elastomers possess several unique characteristics including excellent abrasion resistance and oil resistance. They are used in a wide variety of commercial and Defense applications. In this work, the effect of a newly developed graphene surfactant (GOS) on the thermal, mechanical and viscoelastic properties of vulcanized latex nanocomposites was studied. The latex was synthesized by emulsion polymerization and the vulcanized film without any filler had a tensile strength (TS) of 2.40?MPa and strain at break of 107%. Graphite filler (8?wt%) in combination with 2.6?wt% of GOS, added to the latex, increased the TS to 5.2?MPa and to 7.5?MPa with 10?wt% of the GOS, while the elongation at break was reduced to 48% and 30% for the latex nanocomposites, respectively. The vulcanized film without any graphite, but with 2.8?wt% of GOS had a TS of 7.8?MPa and a marginally increased elongation at break (88%), as compared to the graphite filled composites. The nanocomposites with graphite and GOS also showed higher damping characteristics, as indicated by the width of the tan δ peak, spanning over a broad temperature range of 100?°C for the sample with 2.6?wt% GOS and 8?wt% graphite. In summary, the work reports the development of potentially valuable damping materials from carboxylated nitrile latex using an amphiphilic polymer modified graphene surfactant in combination with graphite.     

Preparation, characterization and properties of amino-functionalized montmorillonite and composite layer-by-layer assembly with inorganic nanosheets

An amino-functionalized montmorillonite (APTMS-MMT) was prepared by the grafting of 3-aminopropyltrimethoxysilane (APTMS) on the surface of MMT via the ultrasonic synthesis process and characterized by a variety of techniques: FT-IR, thermogravimetic analysis (TGA), particles size analysis and ζ-potential measurement. The results showed the size and size distribution of APTMS-MMT particles were decreased, and the ζ-potential of particles was increased obviously via the ultrasonic synthesis process. The particles of 30% APTMS-MMT_US (MMT modified with 30 wt% APTMS with ultrasonic synthesis process) had a z-average diameter of about 500 nm and a polydispersity index of 0.2. The resultant 30% APTMS-MMT_US was dispersed uniformly and stably in water. The poly(acrylic acid) (PAA)/APTMS-MMT multilayer films were grown through layer-by-layer (LBL) deposition of PAA and APTMS-MMT. SEM results indicated that the ultrasonic synthesis of APTMS-MMT increased dispersability of clay sheets at high loadings. The thermal stability and mechanical properties of PAA/APTMS-MMT composites were investigated by TGA and tensile test respectively. The results showed the ultrasonic synthesis of APTMS-MMT enhanced the thermal stability and mechanical properties of PAA/APTMS-MMT composites significantly. PAA/30% APTMS-MMT_US composite displayed 3 times higher strength and 6 times higher Young's modulus when compared with pure PAA polymer.     

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.     

Morphology and Mechanical Performance of Polysulfone Modified by a Glass Fiber Reinforced Liquid‐Crystalline Polymer

Abstract

Hybrid composites based on polysulfone of bisphenol A (PSF) and glass fiber (GF) reinforced copolyester liquid‐crystalline polymer (gLCP) were obtained by injection molding. The viscosity of the 10% and 20% gLCP composites was lower than that of pure PSF. The Young's modulus followed the direct rule of mixtures. This was due to the counteracting effects of the decreasing orientation of the liquid‐crystalline polymer (LCP) in the skin at increasing gLCP contents on the one hand; and either the increasing skin thickness in the PSF‐rich composites or the lower orientation of the core in the PSF‐poor composites on the other. The composites with 10–20% gLCP showed the best mechanical performance, because, besides their enhanced processability, they showed a tensile strength similar to that of PSF and much larger notched impact strength.     

Preparation of graphene/PMMA composites with assistance of ultrasonic wave under supercritical CO2 conditions

The two-dimensional material graphene has many excellent physicochemical properties such as large specific surface area, high electron migration rate, good chemical properties, good thermal conductivity, high elastic modulus and mechanical strength that make it very valuable for theoretical research and application in the preparation of graphene/polymer composites. In this paper, the effects of ultrasonic intensity and reaction time on the molecular weight and yield of PMMA under supercritical CO₂ conditions were investigated. It was found that there are threshold and optimal values of ultrasonic intensity for initiating the reaction in supercritical CO₂ system. The threshold value is 150 W/cm² and the optimal ultrasonic intensity value is 225 W/cm². There is also an optimal value of ultrasonic initiation time for ultrasonic initiation polymerization. Combining the reaction yield and the molecular weight of the product, 2 h of ultrasonic initiation is a suitable initiation reaction time. Based on the synthesis of PMMA by ultrasonic excitation, the preparation of Graphene/PMMA composites by ultrasound assistance was also investigated. The TG and DTG characterization of PMMA and complex materials prepared by ultrasonic excitation showed that the radicals generated by ultrasonic excitation were uniformly distributed and did not generate unsaturated double bonded polymers. The electrical conductivity of the Graphene/PMMA composites prepared by ultrasonic excitation at a graphene content of 1 wt% increased to 1.13 × 10^-1 S/cm, which is better than that of the Graphene/PMMA prepared by in situ polymerization. This may be attributed to the ultrasound-assisted supercritical CO₂ fluid action that resulted in a more uniform distribution of Graphene mixed with PMMA in the prepared composites. Therefore, it is of important practical significance for the preparation of Graphene/PMMA composites by ultrasound-induced polymerization.     

Study on the Structure and Properties of UHMWPE/Epoxy Resin Composite Fiber

The preparation, crystallization behavior, and fiber structure and properties of ultrahigh molecular weight polyethylene (UHMWPE) epoxy resin composite fiber were studied by means of differential scanning calorimeter (DSC), X‐ray diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and tensile testing. The morphology showed a different behavior from pure polyethylene (PE) fiber. The fiber mechanical properties, creep behavior, and thermal properties of UHMWPE fiber can be improved by adding epoxy resin. It's believed that the epoxy can serve as a physical cross‐linking agent to limit the motion or migration of PE molecules and consequently improve the fiber creep property. However, when the content of epoxy resin is higher than 5 wt%, all of the behavior and properties deteriorate.     

Fractal and structural aspects of adhesion in particulate-filled polymer composites

Two types of composites based on poly(hydroxy ether) and graphite with various amounts of a filler have been investigated by various methods. The methods have been used to estimate the characteristics of adhesion and interfacial layer, including its thickness and tensile strength and interdependence between these values and adhesion. The results are treated on the basis of the theory of irreversible aggregation, cluster theory of the polymer structure and fractal analysis. It is established that all important characteristics of adhesion, interfacial layer and mechanical properties are interconnected with the difference between fractal dimensions of the surface of the aggregates of filler particles and of a polymer matrix, whose structure is distorted under the influence of the filler surface.     

Physical properties of a high molecular weight hydroxyl-terminated polydimethylsiloxane modified castor oil based polyurethane/epoxy interpenetrating polymer network composites

A series of polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The effects of HTPDMS content on the phase structure, damping properties and the glass transition temperature (Tg) of the HTPDMS-modified PU/EP IPN composites were studied by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of the composites increased with the increase of HTPDMS content. The tensile strength and impact strength of the IPN composites were also significantly improved, especially when the HTPDMS content was 10%. The modified IPN composites were expected to be used as structural damping materials in the future.     

Thermal and Mechanical Properties of Poly(lactic acid)/Modified Carbon Black Composite

Poly(ethylene glycol) (PEG) was added as a plasticizer to the composite of poly(lactic acid) (PLA) and a modified carbon black (MCB). Among the three different molecular weight (M_n = 1000, 2000, 6000) PEGs used, PEG2000 promoted crystallization of PLA and enhanced the nucleation activity of MCB more efficiently than the other two. The crystallization rate of PLA/PEG2000/3 wt% MCB composite was three times that of PLA. Although a small decrease in tensile strength and modulus of elasticity of the composite was found as the PEG content increased, the elongation at break of the PLA/PEG/MCB composites significantly improved. When the PEG2000 content was 15 wt%, the elongation at break of the blend was 90%, 4.5 times that of the neat PLA.