Some of the mechanical and thermal properties of wheat straw filled-PP composites

The objective of this investigation was to evaluate the mechanical, thermal stability and viscoelastic behaviors of experimental PP composites made from wheat straw and PP-g-MA coupling agent. Four levels of wheat straw, 10, 20, 25 and 30 wt % and two levels of coupling agent, 0 and 3 % wt were mixed with PP in rotary type mixer and injection molding process, respectively. Tensile characteristics and impact strength, thermal gravity and dynamic mechanical and thermal analysis of the samples were evaluated. Based on the results, it was observed that the tensile properties increased and impact strength decreased with the increase in the fiber loading from 10 % to 30 %. Further, the composites treated with PP-g-MA exhibited improved mechanical properties which confirmed efficient fiber-matrix adhesion. DMT analysis showed that the PP composites made of 30 % wheat straw containing 3 % PP-g-MA showed the highest E’ and lowest tan δ than the untreated ones. Also, the thermal stability of wheat straw was lower than PP and as filler content in the composites increased, the thermal stability decreased and the ash content increased.     

Nano-SiO2 filled rice husk/polypropylene composites: Physico-mechanical properties

In this research, reinforcing effect of hybrid filler including rice husk (RH), beech bark (BB) and nano-SiO₂, in polypropylene has been investigated. In the sample preparation, four levels of filler loading were used for waste lignocellulosic materials (55-58 wt.%) and nano-SiO₂ (0-4 wt.%). In order to increase the interphase adhesion, polypropylene grafted with maleic anhydride was added as a coupling agent to all the composites studied. The physical properties, viz. the thickness swelling and water absorption, and mechanical properties, namely, the tensile, flexural and notched Izod impact strengths, of the composites were determined. Generally, high amount of filler content in composites can lead to the reduction of interfacial adhesion between matrix polymer and filler, and it limits their applications. The results showed that while flexural properties and elongation at break were moderately improved by the increase in the amount of filler in the matrix, tensile and Izod impact strengths decreased dramatically. However, the composites had acceptable mechanical strength levels. The mechanical properties of composites filled with RH are generally greater than BB composites. The thickness swelling and water absorption of the composites increased with the increase in the filler loading, but to a negligible extent as compared with the wood-based composites and the solid woods. Nano-SiO₂ addition showed little positive effect on the mechanical properties. It can be concluded from this study that the used waste lignocellulosic materials are attractive reinforcements from the standpoint of their physico-mechanical properties.     

Effects of surface treatment of ramie fibers in a ramie/poly(lactic acid) composite

The chemical and morphological properties of ramie fibers treated by chemical surface modification were examined with Fourier transform infrared (FT-IR) spectroscopy. The mechanical and thermal decomposition properties were evaluated with respect to tensile strength, tensile modulus and thermogravimetric analysis (TGA). Surface morphological changes were investigated with scanning electron microscopy (SEM). Finally, the capabilities of composites reinforced with various chemically treated fibers were analyzed by investigating tensile and impact strengths. Additionally, the thermal mechanical properties of the composites were investigated with thermal mechanical analysis (TMA). Based on the results of these analyses, we concluded that pectin, lignin and hemicellulose were removed and thermal stability was increased with chemical treatments. The composites reinforced with ramie fiber showed better properties compared with pure PLA matrix with respect to tensile and impact strengths. The peroxide-treated fiber composite had the smallest thermal expansion.     

Si-Al hybrid effect of waterborne polyurethane hybrid sizing agent for carbon fiber/PA6 composites

The interface of fiber-reinforced composites has remained a vexing problem that limits the use of the excellent properties of carbon fiber (CF) in composite applications. In the present study, waterborne polyurethane (WPU) hybrid sizing agents were prepared to improve the performances of CFs and the interface strength of CF/PA6 composites. The structural and mechanical properties of the single-CF and CF/PA6 composites were systematic investigated. The results showed that the mechanical properties of the CF/PA6 composites were significantly improved by adding of WPU hybrid sizing agent. The tensile and flexural strengths of the WPU/SiO₂/Al₂O₃ hybrid sizing agent treated CF/PA6 composites were increased by 24.0 % and 25.7 % than those of no-sizing treated CF/PA6 composites, respectively.     

Effects of heat treatment on the properties of bamboo fiber/polypropylene composites

In this paper, the effects of heat treated parameters on the properties of bamboo fiber (BF) / polypropylene (PP) composites were investigated. The crystallization properties of BF/PP composites after heat treatment were characterized by differential scanning calorimetry (DSC), and the mechanical properties were measured. The results showed that the crystallinities of the heat treated composite were enhanced compared with that of the untreated. When the heat treated time was 30 mins, the crystallinities became almost unchanged. However, the crystallinity decreased after 12 h heat treatment. In addition, when the heat treated temperature was above 90 °C, the higher the temperature was, the higher the crystallinities became. Moreover, the tensile strengths of BF/PP composites increased and then decreased with increasing heat treated time, while the impact strengths had a decreasing trend. In the meanwhile, the tensile strengths increased but the impact strengths decreased as the heat temperature increased.     

Polypropylene/high-density polyethylene/carbon fiber composites: Manufacturing techniques,mechanical properties,and electromagnetic interference shielding effectiveness

This study uses polypropylene (PP)/high-density polyethylene (HDPE) polyblends (80/20 wt.%) as matrices, which are then melt-blended with inorganic carbon fibers (CF) as reinforcement to form electrically conductive PP/HDPE composites. Tensile test, flexural test, Izod impact test, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) are performed to evaluate different physical properties of samples. A surface resistance and electromagnetic interference shielding effectiveness (EMI SE) measurements are used to evaluate the electrical properties of the PP/HDPE/CF composites. Test results show that an increasing content of carbon fibers results in an 18 %, 23 %, and 60 % higher tensile strength, flexural strength, and impact strength, respectively. SEM results show that carbon fibers break as a result of applied force, thereby bearing the force and increasing the mechanical properties of composites. DSC and XRD results show that the addition of carbon fibers causes heterogeneous nucleation in PP/HDPE polyblends, thereby increasing crystallization temperature. However, the crystalline structure of PP/HDPE composites is not affected. Surface resistivity results show that 5 wt.% of carbon fibers can form a conductive network in PP/HDPE polyblends and reduce the surface resistivity from 12×10¹² ohm/sq to 4×10³ ohm/sq. EMI SE results show that, with a 20 wt.% CF and a frequency of 2-3 GHz, the average EMI SE of PP/HDPE/CF composites is between -48 and -52 dB, qualifying their use for EMI SE, which is required for standard electronic devices.     

Effect of nanoclay incorporation method on mechanical and water vapor barrier properties of starch-based films

The objective of this study was to investigate the influence of nanoclay incorporation procedure on the mechanical and water vapor barrier properties of starch/nanoclay composite films. Cassava starch films were prepared with (nanocomposite) and without nanoclay (control) in two steps: firstly the production of extruded pellets and secondly thermo-pressing. The nanocomposite films were prepared via two different methods: in D samples the nanoclay was dispersed in glycerol and subsequently incorporated into the starch; and in ND samples all ingredients were added in a single step before the extrusion. All the composite-films were prepared with cassava starch using 0.25 g of glycerol/g of starch and 0.03 g of nanoclay/g of starch. Control samples showed V_A-type crystallinity induced by the manufacturing process and the nanocomposites presented a semicrystalline and intercalated structure. The nanoclay improved the water vapor barrier properties of the starch film and this effect was more pronounced in D samples, where the water vapor permeability (K^w) was 60% lower than that of the control samples. The K^w reduction was associated with decreases in the effective diffusion coefficient (approximately 61%) and in the coefficient of solubility (approximately 22-32%). On the other hand, the incorporation of nanoclay increased the tensile strength and the rigidity of the films and this effect was more significant when the nanoclay was dispersed in glycerol. Thus, the incorporation of nanoclay into starch-based films is a promising way to manufacture films with better mechanical and water vapor barrier properties.     

Effects of nanoclay and short nylon fiber on morphology and mechanical properties of nanocomposites based on NR/SBR

Natural rubber and styrene butadiene rubber (NR/SBR) reinforced with both short nylon fibers and nanoclay (Cloisite 15A) nanocomposites were prepared in an internal and a two roll-mill mixer by a three-step mixing process. The effects of fiber loading and different loading of nanoclay (1, 3 and 5 wt. %) were studied on the microstructure and mechanical properties of the nanocomposites. The adhesion between the fiber and the matrix was improved by the addition of a dry bonding system consisting of resorcinol, hexamethylene tetramine and hydrated silica (HRH). This silicate clay layers was used in place of hydrated silica in a HRH bonding system for SBR/NR-short nylon fiber composite. Nanoclay was also used as a reinforcing filler in the matrix-short fiber hybrid composite. The cure and scorch times of the composites decreased while cure rate increased when the short fiber and nanoclay were added. The mechanical properties of the composites showed improvement in both longitudinal and transverse directions with increasing short fiber and nanoclay content. The structure of the nanocomposites was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM). X-ray diffraction results of nanocomposites indicated that the interlayer distance of silicate layers increased. The mechanical properties of nanocomposites (tensile, hardness and tear strength) are examined and the outcome of these results is discussed in this paper.     

Effect of temperature and time on mechanical and electrical properties of HDPE/glass fiber composites

In recent years, composites based on glass fiber reinforced polymer have been widely used in order to meet increasing durability and safety regulations, particularly in the power cable, automotive and plane industry. In this paper, mechanical and electrical properties of high density polyethylene (HDPE) and HDPE containing glass fiber polymer composites were investigated and compared at different temperatures. Composite materials were prepared with the hot pressing method. Tensile strength, % elongation and the modulus of elasticity (or Young’s modulus) were determined for each sample at different temperatures. In addition to this, at different temperatures τ _σ and τ _E have mechanical and electrical lifetime respectively, corresponding to mechanical tension (σ) and electrical strength (E), and this was investigated for each sample. As compared to the mechanical and electrical properties of neat HDPE, HDPE/0.5 % glass fiber composites have been found to have better mechanical and electrical durability.     

Assessment of the mechanical properties of nanoclays enhanced low Tg epoxy resins

The mechanical properties of the nanocomposites are dependent, not only of the clays content but, also, of the resin type and manufacturing process. In this context, the present study intends to develop a systematic study involving a low glass transition temperature (T_g) and low permeability epoxy resin (SR 1500 and the hardener SD 2503) with a commercially Nanomer I30 E nanoclays. Two dispersion processes were compared (direct (DM) and indirect method (IDM)) in terms of mechanical properties, as well as the influence of nanoclay content and hydro aging effect. It was possible to observe that the composites obtained by the indirect method present lower mechanical properties than the neat resin because there is residual acetone. For DM composites the tensile strength, fracture toughness and the specific energy absorbed by impact decreases with the reinforcement content, caused by particle agglomerates. Elastic modulus, at 25 °C, increases significantly and T_g increases slightly with the addition of nanoclays. Hydro aging promotes a progressive decreasing of the tensile strength and fracture toughness, with the clay content, reaching about 15 % and 7 %, respectively, for 6 wt% of nanoclays. On the other hand, a small increasing on specific energy absorbed was observed.     

Electrospun poly(ɛ-caprolactone)/nanoclay nanofibrous mats for tissue engineering

Nanofibrous mats of poly (?-caprolactone)/nanoclay nanocomposites were fabricated using electrospinning method. Effects of nanoclay content of the nanocomposite on final nanofiber structures were investigated and characterized by scanning electron microscope (SEM) and differential scanning calorimetry (DSC) analysis. The results showed that the presence of the nanoclay promoted the creation of fibrous structure in comparison with solely poly (?-caprolactone). Furthermore, increase in nanoclay content led to the formation of more uniform nanofiber structures and caused a decrease in the mean nanofiber diameter. DSC results showed that the addition of nanoclay reduced the crystallinity of the nanocomposite in compared with pristine PCL. Studies of the mechanical properties, wettability and degradability showed that the presence of nanoclay improved tensile modulus, tensile strength, wettability and biodegradability of the nanocomposites. To evaluate the effect of nanoclay on the cell adhesion and bioactivity of the poly (?-caprolactone)/nanoclay nanocomposites, fibroblasts cells were seeded on the mats. The results showed that the prepared nanocomposite could be a potential candidate for tissue engineering.     

Effect of the low and radio frequency oxygen plasma treatment of jute fiber on mechanical properties of jute fiber/polyester composite

We investigated the surface modification of jute fiber by oxygen plasma treatments. Jute fibers were treated in different plasma reactors (radio frequency “RF” and low frequency “LF” plasma reactors) using O₂ for different plasma powers to increase the interface adhesion between jute fiber and polyester matrix. The influence of various plasma reactors on mechanical properties of jute fiber-reinforced polyester composites was reported. Tensile, flexure, short beam shear tests were used to determine the mechanical properties of the composites. The interlaminar shear strength increased from 11.5 MPa for the untreated jute fiber/polyester composite to 19.8 and 26.3 MPa for LF and RF oxygen plasma treated jute fiber/polyester composites, respectively. O₂ plasma treatment also improved the tensile and flexural strengths of jute fiber/ polyester composites for both plasma systems. It is clear that O₂ plasma treatment of jute fibers by using RF plasma system instead of using LF plasma system brings about greater improvement on the mechanical properties of jute/polyester composites.     

Mechanical and machinability behaviors of woven coir fiber-reinforced polyester composite

The research on coir-polyester composites initiated the interest in the development of woven coir fiber-reinforced polyester composites. The mechanical properties of woven coir-polyester composites were evaluated as per ASTM standards and the machinability behavior was studied by conducting drilling tests in this investigation. The woven coir-polyester composites exhibited the average values of tensile, flexural and impact strength of 19.9 MPa, 31.3 MPa and 49.9 kJ/m² respectively. The effect of NaOH treatment on the improvement of mechanical properties of woven coir-polyester composites were studied in this investigation. The 40 % increase of tensile strength, 42 % increase of flexural strength and 20 % increase of impact strength were achieved by treated woven coir fiber-reinforced polyester composites. The regression models for predicting thrust force, torque and tool wear in drilling of woven coir-polyester composites were developed and the effect of drilling parameters were analyzed.     

Mechanical characterization of clay reinforced polypropylene nanocomposites at high temperature

This paper focuses on the influence of temperature conditions and the clay contents on enhancement of mechanical characterization of polypropylene (PP) nanocomposites. The nanocomposites were prepared using the melt mixing technique in a co-rotating intermeshing twin screw extruder followed by injection moulding. Nanocomposites properties such as impact strength and ultimate tensile strength, yield strength, failure strain, Young’s modulus and toughness are calculated. The addition of clay to PP matrix was showed remarkable enhancement in mechanical properties at the temperature of 25 oC and 120 °C. Nearly 36 % and 160 % increase in the Young’s modulus and about 45 % and 62 % increase in the impact strength were observed at both room temperature (RT) and high temperature (HT), respectively. But, the tensile strength was not affected much. The basal spacing of clay in the composites was measured by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to assess the surface morphology of the fractured surfaces and dispersion of the nanoclay.     

Surface treatments of jute fabric: The influence of surface characteristics on jute fabrics and mechanical properties of jute/polyester composites

In this study, jute fabrics were modified by alkali, micro-emulsion silicon (MS) and fluorocarbon based agents (FA) in order to enhance the interfacial adhesion between the polyester matrix and the jute fiber. X-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to characterize fiber surfaces. The effects of various surface treatments on the mechanical and morphological of jute/polyester composites were also studied. All surface treatments were shown to improve the tensile, flexural strengths and interlaminar shear strengths of the composites. Moreover, the maximum improvement in the mechanical properties was obtained for the FA treated jute/polyester composites. SEM micrographs of the tensile fracture surface of jute/unsaturated polyester composites also exhibited improvement of interfacial and interlaminar shear strengths by the alkali, MS and FA treatments of jute fibers.     

Evaluating the Mechanical Behavior of Basalt Fibers/Epoxy Composites Containing Surface-modified CaCO<Subscript>3</Subscript> Nanoparticles

Polymer matrix composites (PMCs) owing to their outstanding properties such as high strength, low weight, high thermal stability and chemical resistance are broadly utilized in various industries. In the present work, the influence of silanized CaCO₃ (S-CaCO₃) with 3-aminopropyltrimethoxysilane (3-APTMS) coupling agent at different values (0, 1, 3 and 5 wt.% with respect to the matrix) on the mechanical behavior of basalt fibers (BF)/epoxy composites was examined. BF-reinforced composites were fabricated via hand lay-up technique. Experimental results from three-point bending and tensile tests showed that with the dispersion of 3 wt.% S-CaCO₃, flexural strength, flexural modulus, tensile strength and tensile modulus enhanced by 28 %, 35 %, 20 % and 30 %, respectively. Microscopic examinations revealed that the development of the mechanical properties of fibrous composites with the incorporation of modified CaCO₃ was related to enhancement in the load transfer between the nanocomposite matrix and BF as well as enhanced mechanical properties of the matrix part.     

Basic properties of grain by-products and their viability in polypropylene composites

The objective was to study the potential of grain by-products (husk) of grains such as wheat (Triticum aestivum L; German name is Weizen) and rice (Oryza sativa) as reinforcements for thermoplastics as an alternative to or in combination with wood fibres. Prior to composites preparation, the chemical components of fibres such as cellulose, hemi-cellulose, lignin, starch, protein and fat were measured and the surface chemistry and functionality of grain by-products were studied using EDX and FT-IR. Structural constituents (cellulose, starch) were found in wheat husk (W) equal 42%, in rice husk 50% and in soft wood 42%, respectively. Thermal degradation characteristics, the bulk density, water absorption and the solubility index were also investigated. Wheat husk (W) and rice husk were found thermally stable at temperatures as low as 178 °C and 208 °C, respectively. The particle morphology and particle size were investigated using microscopy. Water absorption properties of the fibres were studied to evaluate the viability of these fibres as reinforcements. Polypropylene composites were fabricated using a high speed mixer and an ensuing injection moulding process with 40 wt% fibre. The tensile and Charpy impact strength of the resulting composites were investigated. The tensile elongation at break was found to 75% for wheat husk (W) composites and 23% for rice husk composites better than soft wood composites. Rice husk composites showed 13% better Charpy impact strength than soft wood composites. Due to coupling agent, tensile strength of composites found to improve 25% for soft wood, 35% for wheat husk (W) and 45% for rice husk.     

Thermal transitions of the amorphous polymers in wheat straw

The thermal transitions of the amorphous polymers in wheat straw were investigated using dynamic mechanical thermal analysis (DMTA). The study included both natural and solvent extracted wheat straw, in moist (8-9% water content) and dry conditions, and was compared to spruce samples. Under these conditions two transitions arising from the glass transition of lignin and hemicelluloses have been identified. Key transitions attributed to softening of lignin were found at 53, 63 and 91 °C for moist samples of wheat straw, extracted straw and spruce, respectively. Transitions for hemicelluloses were determined at 2, −1 and 5 °C, respectively. Differences are likely due to different compositions of lignin and hemicelluloses from straw and spruce and structural differences between the raw materials. The high wax content in wheat straw resulted in a transition at about 40 °C which was absent in solvent extracted wheat straw samples and spruce. This specific transition was further investigated and confirmed by differential scanning calorimetry (DSC) of extracted wheat straw wax. Information about the thermal transitions is of great importance for the utilization of wheat straw in pelletizing, briquetting and fiber board manufacturing.     

Recycling of rice straw to improve wheat yield and soil fertility and reduce atmospheric pollution

Burning of rice straw is a common practice in northwest India, where rice–wheat cropping system is extensively followed. The practice results in loss of nutrients, atmospheric pollution and emission of greenhouse gases. A field experiment was conducted at Indian Agricultural Research Institute, New Delhi, India during the rabi season (November to April) of 2002–2003 to evaluate the efficacy of the various modes of rice straw recycling in soil in improving yield and soil fertility and reducing not only carbon dioxide emission but also nitrous oxide (N₂O) emission. The treatment with no rice straw incorporation and application of recommended doses of fertilizer (120, 26 and 50 kg N, P and K ha⁻¹, respectively), gave the highest yield of wheat. Treatments with the incorporation of rice straw at 5 Mg ha⁻¹ with additional amount of inorganic N (60 kg N ha⁻¹) or inoculation of microbial culture had similar grain yields to that of the treatment with no straw incorporation. The lowest yield was recorded in the plots where rice straw was incorporated in soil without additional inorganic N and with manure application. All the treatments with rice straw incorporation had larger soil organic C despite the effect on the mineralisation of soil organic matter. Emission of N₂O was more when additional N was added with rice straw and secondary when straw was added to the soil because of higher microbial activity. The study showed that burning of rice straw could be avoided without affecting yield of wheat crop by incorporating rice straw in soil with an additional dose of inorganic N or microbial inoculation. However, the reduction of N₂O emission due to avoiding burning is in part counterbalanced by an increase in emission during the subsequent wheat cultivation.     

Morphology and mechanical properties of thermo-molded bioplastics based on glycerol-plasticized wheat gliadins

Glycerol-plasticized wheat gliadin bioplastics were prepared through thermo-molding method. The effect of glycerol content on the morphology and the mechanical properties of wheat gliadin bioplastics was studied. Morphology, tensile properties (tensile strength and elongation at break), dynamic mechanical properties and rheological properties were evaluated in relation to glycerol content. Experimental results reveal that the morphology, the glass transition temperatures (T_g) of both the gliadin-rich and the glycerol-rich domains and the tensile properties are closely linked to the glycerol content. The time–temperature superposition (TTS) fails to be applied to the dynamic loss modulus G″ (all temperatures) and the dynamic storage modulus G′ (above 80 °C) of wheat gliadin bioplastics.