Effect of crystallite size of zinc oxide on the mechanical,thermal and flow properties of polypropylene/zinc oxide nanocomposites

ZnO nanoparticles were prepared using zinc chloride and sodium hydroxide in chitosan medium. Prepared ZnO (NZO) and commercial ZnO (CZO) was characterized by scanning electron microscopic and X-ray diffraction studies. PP/ZnO nanocomposites were prepared using 0–5 wt% of zinc oxide by melt mixing. It was then compression moulded into films. Transparency of the composite films were improved by reducing the crystallite size of ZnO. Melt flow index studies revealed that NZO increased the flow characteristics of PP while CZO decreased. X-ray diffraction studies indicated α-form of isotactic polypropylene. An increase in mechanical properties, dynamic mechanical properties and thermal stability of the composites were observed by the addition of ZnO. Uniform dispersion of the ZnO was observed in the scanning electron micrographs of the tensile fractured surface of composites.     

Study on the mechanical properties and thermal properties of jute and banana fiber reinforced epoxy hybrid composites

The aim of the present study is to investigate and compare the mechanical and thermal properties of raw jute and banana fiber reinforced epoxy hybrid composites. To improve the mechanical properties, jute fiber was hybridized with banana fiber. The jute and banana fibers were prepared with various weight ratios (100/0, 75/25, 50/50, 25/75 and 0/100) and then incorporated into the epoxy matrix by moulding technique to form composites. The tensile, flexural, impact, thermal and water absorption tests were carried out using hybrid composite samples. This study shows that addition of banana fiber in jute/epoxy composites of up to 50% by weight results in increasing the mechanical and thermal properties and decreasing the moisture absorption property. Morphological analysis was carried out to observe fracture behavior and fiber pull-out of the samples using scanning electron microscope.     

Preparation and bending properties of three dimensional braided single poly (lactic acid) composite

New three dimensional (3D) braided single poly (lactic acid) composites (PLA–SPCs) were obtained by combining 3D and five (5)-direction braiding technique and hot-compression technical process. 3D and 5-direction braided preforms with different braiding angles, thicknesses and fiber volume fractions were prepared. Preforms were preheated in the specially designed die system in order to make all of the fibers partially melted. In the next stage, the preforms were consolidated under a certain pressure (from 7.8 to 10 MPa) at temperatures ranging from 130 up to 150 °C. Under the controlled processing conditions, one part of fiber body formed matrix while the other part retained its fibrous form.At the same consolidation temperature, the maximum bending stress values resulted to be substantially dependent on the fiber volume fraction of PLA–SPCs, while the bending modulus values were largely subjected to the fiber content in the length direction. The increases of consolidation pressure gave rise to better fusion of neighboring fibers with the result that the maximum stress and modulus were increased. As the consolidation temperature increases, the fusion bonding was improved, the bending failure feature was converted from plastic to brittle, both maximum bending stress and modulus values were increased. It is expected that this study could provide a new approach for the manufacture of high-performance single polymer composites (SPCs) by using thermoplastic polymer fibers.     

A comparison of the mechanical characteristics of kenaf and lyocell fibre reinforced poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) composites

Cellulose fibre-reinforced poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) composites have become increasingly interesting with regard to their biodegradability and mechanical characteristics. The use of different matrices leads to variable composite characteristics. This study provides a comparison of the mechanical characteristics of compression-moulded 30 mass% lyocell and 40 mass% kenaf fibre-reinforced PLA and PHB. The results of the tensile tests showed that 30 mass% lyocell/PLA composites reached the highest tensile and bending strength with 89 and 148 N/mm², respectively. The highest Young’s modulus was also measured for 30 mass% lyocell/PLA with 9.3 GPa, and the highest flexural modulus was measured for 40 mass% kenaf/PHB with 7.1 GPa. By far, the best impact strength was determined for lyocell/PHB with 70 kJ/m², followed by lyocell/PLA with 52 kJ/m². The investigation of the Shore D hardness resulted in a higher value for the PLA matrix with 81.5. PHB achieved a hardness of 67.5. By adding fibres as reinforcement, the Shore D hardness increased up to 83.6 for lyocell/PLA and 73.1 for kenaf/PHB. Density measurements showed lower densities for the composites with higher fibre loads (kenaf/PLA and kenaf/PHB) in comparison to the theoretical density. This speaks for a higher proportion of air inclusion in the composites which could negatively affect the mechanical composite characteristics.     

Mechanical properties of epoxy composites filled with silane-functionalized graphene oxide

In this work, the effects of as-produced GO and silane functionalized GO (silane-f-GO) loading and silane functionalization on the mechanical properties of epoxy composites are investigated and compared. Such silane functionalization containing epoxy ended-groups is found to effectively improve the compatibility between the silane-f-GO and the epoxy matrix. Increased storage modulus, glass transition temperature, thermal stability, tensile and flexural properties and fracture toughness of epoxy composites filled with the silane-f-GO sheets are observed compared with those of the neat epoxy and GO/epoxy composites. These findings confirm the improved dispersion and interfacial interaction in the composites arising from covalent bonds between the silane-f-GO and the epoxy matrix. Moreover, several possible fracture mechanisms, i.e. crack pinning/deflection, crack bridging, and matrix plastic deformation initiated by the debonding/delamination of GO sheets, were identified and evaluated.     

Mechanical properties of textile-inserted PP/PP knitted composites using injection–compression molding

This paper concentrates on the experimental investigation of the self-reinforced all-polypropylene composites. There exists an optimum processing condition to produce high quality specimens by injection–compression molding. Tensile and 3-point bending properties of the virgin PP materials were nearly unaffected by the introduction of reinforcing knit layer(s) due to very low fibre content of the knitted fabrics used. 3-point bending properties were also unaffected by the surface of indentation-flexure. The applied impact energy was maintained at 5 J for the homo-PP and 27 J for the block-PP materials, respectively, to cause penetration during drop-weight impact tests. It is interestingly noteworthy that the self-reinforced homo-PP composites exhibited superior energy absorption capability when compared with the virgin matrix materials. The corresponding plate bending performances of the self-reinforced homo-PP composites also revealed consistent improvement as compared to their virgin counterparts. On the other hand, although virgin block-PP material exhibited better impact performances than its composite reinforced by the homo-PP knitted fabric, a notably small increase in the reinforcement fibre content revealed considerable improvement in the impact properties comparable to those of the virgin block-PP matrix materials. These self-reinforced homo-PP/block-PP materials have clearly indicated that they have the potential to out-perform the block-PP materials via modification and/or manipulation of the reinforcement knit structural/geometrical parameters and the content of reinforcement fibres. Both static and dynamic impact properties are likely to be affected by the local area properties of the tested face under indentation, and thereby contributing to the improved performances of the composite specimens with the knit face under the impact.     

Crystalline morphology and properties of multi-walled carbon nanotube filled isotactic polypropylene nanocomposites: Influence of filler size and loading

Isotactic polypropylene (PP) nanocomposites with multi-walled carbon nanotubes (MWCNTs) of various diameters (10–50 nm) were fabricated by extrusion and compression-molding techniques and characterized by X-ray diffraction measurements, differential scanning calorimetry, scanning electron microscopy, mechanical test and differential thermal analyses. The pure PP exhibits both the a- and b-axes oriented α-crystal, whereas the MWCNTs induce the b-axis orientation of the α-crystal along with the formation of minor γ-phase crystal in nanocomposites. Crystallinity, long period of lamellae, tensile strength, tensile modulus (TM) and microhardness (H) of PP considerably change by different loading and sizes of MWCNTs. The estimated values H/TM = 0.09–0.10 for all samples approach the predicted value of 0.10 for polymers. The increase in crystallinity has been demonstrated by both XRD and DSC studies. Mathematical models have been invoked to explain the changes in mechanical properties. An increase in thermal stability of polymer matrix occurs with increasing MWCNTs size and loading.     

Effects of raw materials and process parameters on the physical and mechanical properties of flat pressed WPC panels

For the production of WPC, the flat pressing technology can be considered as an alternative to common techniques, particularly when manufacturing large-dimensioned panels. The aim of the present study was to identify and analyze the main influencing parameters on sheets made of wood flour (WF) imbedded in a polypropylene matrix. Test panels were made to measure the effects of panel density, polymer melt flow rate (MFR), WF content, coupling agent, WF size and press temperature on water absorption (WA), thickness swelling (TS), internal bond strength, MOE and MOR. Density, WF content and MFR were identified as main influencing parameters. The increase of density typically leads to an improvement of properties. Lower WF contents cause reduced WA and TS, while the MOE seems to have a maximum at a WF level of 50-70%, depending on raw material used. As an explanation for improving properties when using a high-MFR polymer, a better distribution on the wood surface is hypothesized.     

Development of slate fiber reinforced high density polyethylene composites for injection molding

During the last decade the use of fiber reinforced composite materials has consolidated as an attracting alternative to traditional materials due to an excellent balance between mechanical properties and lightweight. One drawback related to the use of inorganic fibers such as those derived from siliceous materials is the relative low compatibility with conventional organic polymer matrices. Surface treatments with coupling agents and the use of copolymers allow increasing fiber–matrix interactions which has a positive effect on overall properties of composites. In this research work we report the use of slate fiber treated with different coupling agents as reinforcement for high density polyethylene from sugarcane. A silane (propyltrimethoxy silane; PTMS) and a graft copolymer (polyethylene-graft-maleic anhydride; PE-g-MA) were used to improve fiber–matrix interactions on HDPE-slate fiber. The effect of the different compatibilizing systems and slate fiber content were evaluated by scanning electron microscopy (SEM), dynamic thermomechanical analysis (DTMA) as well as mechanical properties (tensile, flexural and impact). The results show that the use of silane coupling agents leads to higher fiber–matrix interactions which has a positive effect on overall mechanical properties. Interesting results are obtained for composites containing 30 wt.% slate fiber previously treated with propyltrimethoxy silane (PTMS) with an increase in tensile and flexural strength of about 16% and 18% respectively.     

Binderless all-cellulose fibreboard from microfibrillated lignocellulosic natural fibres

Fully biobased all-cellulose fibreboards are produced without the use of additional bonding agents such as polymer resins or binders as in the case of e.g. medium density fibreboard (MDF) or natural fibre reinforced plastic (NFRP). These materials make use of the self-binding capability of cellulose, exploiting the enhanced hydrogen bonded network present in micro- and nanofibrillated cellulose, resulting in good mechanical performance. After the optimisation of refinement, drying and hot-pressing conditions, binder-free panels from microfibrillated flax fibres with excellent mechanical properties of around 17 GPa and 120 MPa for flexural modulus and strength, and relatively low water sorption are achieved, making these materials competitive with conventional cellulose based composite materials. The work shows the potential of creating all-cellulose engineering materials using only the intrinsic bonding capacity of microfibrillated lignocellulose, potentially leading to environmentally friendly panel board materials, which are entirely based on renewable resources, recyclable and biodegradable.     

Greatly enhanced cryogenic mechanical properties of short carbon fiber/polyethersulfone composites by graphene oxide coating

In order to employ polyethersulfone (PES) in cryogenic engineering field, its cryogenic mechanical performance should be examined and should also be improved to meet the high requirement for cryogenic engineering application. In this work, pure PES, graphene oxide (GO)/PES, short carbon fiber (SCF)/PES, GO/SCF/PES and GO-coated SCF/PES composites are prepared using the extrusion compounding and injection molding techniques. The tensile and flexural properties of these composites are systematically investigated at a typical cryogenic temperature (77 K). It is shown that the cryogenic mechanical properties are enhanced by the addition of GO, SCFs and coated-SCFs. In particular, the GO-coated SCF/PES composites display the greatly enhanced cryogenic mechanical properties with the highest values compared to other PES composites. In addition, it is exhibited that the cryogenic mechanical properties at 77 K of PES and its composites are far higher than those at room temperature (RT).     

The effect of reprocessing on the mechanical properties of polypropylene reinforced with wood pulp,flax or glass fibre

Composites of polypropylene, substitutable for a given application and reinforced with: Medium Density Fibreboard fibre (MDF) (40 wt%); flax (30 wt%); and glass fibre (20 wt%), were evaluated after 6 injection moulding and extrusion reprocessing cycles. Of the range of tensile, flexural and impact properties examined, MDF composites showed the best mean property retention after reprocessing (87%) compared to flax (72%) and glass (59%). After 1 reprocessing cycle the glass composite had higher tensile strength (56.2 MPa) compared to the MDF composite (44.4) but after 6 cycles the MDF was stronger (35.0 compared to 29.6 MPa for the glass composite). Property reductions were attributed to reduced fibre length. MDF fibres showed the lowest reduction in fibre length between 1 and 6 cycles (39%), compared to glass (51%) and flax (62%). Flax fibres showed greater increases in damage (cell wall dislocations) with reprocessing than was shown by MDF fibres.     

Highly thermally conductive POSS-g-SiCp/UHMWPE composites with excellent dielectric properties and thermal stabilities

Polyhedral oligomeric silsesquioxane grafting thermally conductive silicon carbide particle (POSS-g-SiCp) fillers, are performed to fabricate highly thermally conductive ultra high molecular weight polyethylene (UHMWPE) composites combining with optimal dielectric properties and excellent thermal stabilities, via mechanical ball milling followed by hot-pressing method. The POSS-g-SiCp/UHMWPE composite with 40 wt% POSS-g-SiCp exhibits relative higher thermal conductivity, lower dielectric constant and more excellent thermal stability, the corresponding thermally conductive coefficient of 1.135 W/mK, the dielectric constant of 3.22, and the 5 wt% thermal weight loss temperature of 423 °C, which holds potential for packaging and thermal management in microelectronic devices. Agari’s semi-empirical model fitting reveals POSS-g-SiCp fillers have strong ability to form continuous thermally conductive networks.     

Electromagnetic shielding effectiveness and mechanical property of polymer–matrix composites containing metallized conductive porous flake-shaped diatomite

The porous flake-shaped diatomite particles with different micropores diameter were used as forming templates for the fabrication of the conductive core–shell functional fillers by electroless silver plating. The surface morphologies and phase structures of the surface coatings onto diatomite particles with different micropores diameter were evaluated. The effects of micropores diameter on electrical resistivity, electromagnetic shielding effectiveness and mechanical property of polymer–matrix composites containing silver-coated diatomite particles were also investigated in detail. The results show that the micropores onto initial diatomite particles after plating are completely covered with the coating, while the micropores onto diatomite particles with expanding pores are still visible. The expanding micropores onto diatomite particles in certain size range have less impact on the phase structures, electrical resistivity and electromagnetic shielding effectiveness. However, the mechanical properties of composites are improved significantly after expanding micropores by HF acid corrosion.     

Effect of mechanical activation pretreatment on the properties of sugarcane bagasse/poly(vinyl chloride) composites

This current work is concerned with the pretreatment of sugarcane bagasse (SCB) by mechanical activation (MA) using a self-designed stirring ball mill and surface modification of SCB using aluminate coupling agent (ACA). The untreated and differently treated SCBs were used to produce composites with poly(vinyl chloride) (PVC) as polymer matrix. The activation grade (A_g) measurement and Fourier transform infrared (FTIR) analysis of SCB showed that MA enhanced the condensation reaction between ACA and hydroxyl groups of the SCB fibres, which obviously increased the hydrophobicity of SCB. It was found that the mechanical properties of both the PVC composites reinforced by SCB with and without ACA modification increased with increasing milling time (t_M). Scanning electron microscopy (SEM) analysis showed that MA pretreatment significantly improved the dispersion of SCB in the composites and interfacial adhesion between SCB and PVC matrix, resulting in better mechanical properties of the composites.     

Enhanced thermal conductivity of SiCp/PS composites by electrospinning–hot press technique

Silicon carbide particle/polystyrene (SiCp/PS) electrospun mats are firstly prepared by electrospinning technology, then to be fabricated the corresponding thermally conductive SiCp/PS composites by the method of “laminating-hot press”. The mass fraction of SiCp and laminating mode of SiCp/PS electrospun mats affecting on the thermal conductivities, dielectric and thermal properties of the composites are investigated. The addition of 32.8 vol% SiCp improves the thermally conductive coefficient λ of pure PS from 0.182 to 0.566 W/m K and thermal diffusivity of pure PS from 0.169 to 0.376 mm²/s, whereas the dielectric constant values still remain at relatively low levels. The thermal stabilities of the SiCp/PS composites are increased with the increasing addition of SiCp. For a given SiCp loading, the SiCp/PS composites from warp–weft arrangement of SiCp/PS electrospun mats possess relative higher thermally conductive coefficient λ and dielectric constant values than those of SiCp/PS composites from warp–warp arrangement of SiCp/PS electrospun mats.     

Multi-walled carbon nanotube-filled polyvinyl chloride composites: Influence of processing method on dispersion quality,electrical conductivity and mechanical properties

The influences of dispersion quality and processing conditions on the electrical and mechanical properties of multi-walled carbon nanotube-filled polyvinyl chloride (MWCNT/PVC) composites are examined for potential use in sensor-enabled geosynthetics and other applications involving electrically-conductive polymer composites. Electrical conductivity and mechanical properties of the composite samples made using four different dispersion methods (i.e. probe sonication, bath sonication, mechanical stirring and batch mixing) are measured. Subsurface dispersion in the samples is quantified using laser scanning confocal microscopy and scanning electron microscopy, indicating that MWCNT bundle volumes resulting from all dispersion methods had a log-normal distribution. Dispersion qualities using different mixing methods are compared using the Kolmogorov–Smirnov D-statistic. Findings indicate that samples with higher dispersion quality exhibit greater ultimate strength and failure strain, whereas poorly-dispersed specimens have greater elastic modulus values, which are found to be in good agreement with those predicted by the Halpin–Tsai model.     

On the properties and tribological behaviors of P/M iron based composites reinforced with ultrafine particulates

This paper describes the changes of structure, some mechanical and tribological properties of P/M iron based composites reinforced with ultrafine additives. Nanocrystalline additives of oxides, borides and diamond in the base material allow increasing the compressive strength and the tensile strength 1.5–3 times. An introduction of 0.2–0.3 wt% of ultrafine-grained diamonds, 0.5 wt% of chromium borides and 0.2–0.5 wt% of alumina or oxides mixture provides the best results. The coefficients of friction of MMCs containing nanocrystalline particulates are reduced 2–3 times compared to the base P/M material while the critical seizure pressure is enhanced 2–5 times. The wear resistance of the MMCs increases 2–4 times.     

Characterization of thermoplastic natural fibre composites made from woven hybrid yarn prepregs with different weave pattern

This paper focuses on the effect of weave structure on mechanical behaviour and moisture absorption of the PLA/hemp woven fabric composites made by compression moulding. The unidirectional woven fabric prepregs were made from PLA (warp) and PLA/hemp wrapped-spun hybrid yarn (weft) with two different weave patterns; 8-harness satin and basket. Unidirectional composites with 30 mass% hemp content were fabricated from these prepregs, and compared to winded PLA/hemp hybrid yarn laminates with same composition. The composite from the satin fabric had significantly lowest porosities and best mechanical properties compared to the composite made from the winded hybrid yarn and basket fabric. The tensile, flexural, and impact strength were 88 MPa, 113.64 MPa, and 24.24 kJ/m², respectively. The effect of weave pattern on water absorption is significant. Although the composite from hybrid yarn laminate has larger water absorption than that of the pure PLA, it exhibits lower moisture absorption than both weaves.     

Polyamide-6/vegetal fiber composite prepared by extrusion and injection molding

The interest for the use of vegetal fibers as polymers reinforcement has recently increased because of their unique environmental and technological advantages. This work evaluated the use of Curauá fibers in polyamide-6 composites aiming at glass fiber replacement. Fiber content of 20, 30 or 40 wt% and fiber lengths of 0.1 or 10 mm were studied. Fibers were treated with N₂ plasma or washed with NaOH solution, to improve their adhesion to PA-6. Samples with 20 wt% of short or long fibers, with or without pre-treatment, were compounded in two different co-rotating intermeshing twin-screw extruders. These samples were submitted to mechanical and thermal tests. In conclusion, non-dried raw materials improved fiber/matrix interfacial adhesion. Tensile and flexural properties of this composite are better than unfilled, but lower than glass fiber reinforced polyamide-6. However, its impact resistance and heat deflection temperature are similar to the glass fiber reinforced polyamide-6 and its lower density, enable it to replace this latter in specific non-critical applications.