Enhanced mechanical and thermal properties of carbon fiber composites with polyamide and thermoplastic polyurethane blends

In this article, we demonstrated the preparation of carbon-fiber-reinforced composites using a polyamide 6 (PA6)/thermoplastic polyurethane (TPU) blend, in which the addition of TPU resulted in superior mechanical performances and increased thermal stability. According to various characterization techniques, these results are attributed to an enhanced adhesion and a homogeneous dispersion of long-carbon-fibers (LCFs) with TPU sizing in blended polymer matrix. Above all, dynamic-mechanical thermal analysis (DMTA) measurements clearly show that the dynamic storage modulus (E') of the blend composites is increased by threefold with temperature ranges below and above the glass transition temperature. The presence of LCFs in TPU systems induces effective fiber orientation, exhibiting simultaneous improvements in the tensile strength, flexural strength, and thermal stability.     

Polylactic acid/carbon fiber composites: Effects of functionalized elastomers on mechanical properties,thermal behavior,surface compatibility,and electrical characteristics

In this study, the maleic anhydride grafted styrene-ethylene-butylene-styrene block copolymer (SEBS-g-MA) is used as the compatilizer for polylactic acid (PLA)/carbon fiber (CF) composites. The effects of SEBS-g-MA on the mechanical properties, thermal behavior, interfacial compatibility, and electrical characteristics of composites are then evaluated. The mechanical property tests indicate that when the amount of compatilizer increases, the tensile properties and flexural property of the composites decrease while their impact strength increases. The SEM results show that the compatilizer can decrease the interstices between PLA and CF, and thereby augments their interfacial compatibility. The differential scanning calorimetry (DSC) results confirm that the compatilizer results in a greater crystallization temperature and a greater crystallinity of the composites. The electrical characteristic results indicate that neither PLA nor SEBS-g-MA is not interfered with the conductive network that is constructed by CF, which is exemplified by an average electromagnetic shielding effect of above ?30 dB. This study confirms that SEBS-g-MA can improve interfacial compatibility and toughness, as well as attain good electrical characteristics of PLA/CF composites.     

Electrical properties of novel polyolefin based thermoplastic elastomer and graphene nanocomposites

Numerous efforts to prepare useful graphene-based nanocomposites have been made and important improvements achieved. In our studies, novel structured polyolefin-based thermoplastic elastomer, poly(ethylene-ter-1-hexene-ter-divinylbenzene) (PEHV) was designed and synthesized. And high quality graphene was manufactured via the exfoliation of graphite. PEHV/graphene nanocomposites were fabricated using solution casting method as the amount of graphene added. The morphologies of nanocomposites were observed using scanning electron microscopy. And density, mechanical properties and electrical properties were also measured. Electrical properties and mechanical properties were improved with the increase of graphene added in nanocomposites. It is expected that PEHV/graphene nanocomposites could be applied to lightweight EMI shielding materials.     

Poly(ethylene 2,6-naphthalate)/MWNT nanocomposites prepared by in situ polymerization: Rheological and mechanical properties

Poly(ethylene 2,6-naphthalate)/multi-walled carbon nanotube (PEN/MWNT) nanocomposites are prepared by in situ condensation polymerization in the presence of various acid-treated MWNT (a-MWNT) contents and their morphology, rheological and mechanical properties are investigated as a function of the a-MWNT content. SEM image of a plasma-etched nanocomposite exhibits that a-MWNTs are dispersed well in the PEN matrix by forming an interconnected network structure. Accordingly, rheological properties such as complex viscosities and shear moduli of PEN/a-MWNT nanocomposites at the terminal region of low frequency are much higher than those of pure PEN. Glass transition temperatures of nanocomposites also increase with the increment of the a-MWNT content, which stems from the reduced chain mobility due to the specific interaction between a-MWNTs and PEN matrix. Dynamic and tensile mechanical properties of nanocomposites are also higher than those of pure PEN and they increase with the increment of the a-MWNT content. The highly improved mechanical properties of PEN/a-MWNT nanocomposites are explained to originate from the interconnected network structure of a-MWNTs in PEN matrix as well as the strong interfacial adhesion between a-MWNTs and PEN matrix.     

Preparation and thermal properties of polyphenylene sulfide/organic montmorillonite composites

Cetyl trimethyl ammonium bromide (CTAB) was used for the intercalation modification of nano-montmorillonite (MMT). The spectra of Fourier transform infrared spectrometer (FTIR) and X-ray diffraction (XRD) suggested that CTAB had intercalated into the layers of MMT. And the interlayer spacing of MMT increased from 1.198 to 3.616 nm. The thermogravimetric analysis (TGA) curves of organic montmorillonite (OMMT) showed three-step degradation. The scanning electron microscope (SEM) photographs showed that surface morphology of MMT remained unchanged. Then polyphenylene sulfide (PPS)/organic montmorillonite (OMMT) composites were prepared by melt blending. And composites were treated at 180 °C for 24 h. The results of SEM showed that OMMT had good dispersion behavior and adhesion with PPS. The results of differential scanning calorimetry (DSC) showed the addition of OMMT resulted in heterogeneous nucleation crystallization of PPS. The results of TGA showed there was a good improvement of the thermal stability of PPS. The FTIR and color measurement analysis showed the addition of OMMT could improve the thermal oxidation stability.     

Rheological and thermal properties of acrylonitrile-acrylamide copolymers: Influence of polymerization temperature

An attempt was made to correlate the polymerization temperature and rheological and thermal properties of acrylonitrile (AN)-acrylamide (AM) copolymers. The copolymers were synthesized at different polymerization temperature. The copolymer structure was characterized by gel permeation chromatography (GPC) and Infrared spectrum (IR). The rheological and thermal properties were investigated by a viscometer and differential scanning calorimeter-thermogrametric (DSCTG) analysis, respectively. When the polymerization temperature increased from 41 °C to 65 °C, the molecular weight ([`(M)] <sub>w</sub> )(\overline M _w ) of copolymers decreased from 1,090,000 to 250,000, while its conversion increased from 18% to 63%, and the polymer composition changed slightly. To meet the requirements of carbon fibers, the rheological and thermal properties of products were also investigated. It was found that the relationship between viscosity and [`(M)] _w\overline M _w was nonlinear and the viscosity index (n) decreased from 3.13 to 2.69, when the solution temperature increased from 30 °C to 65 °C. This suggests the dependence of viscosity upon [`(M)] _w\overline M _w is higher at lower solution temperature. According to the result of activation energy, the sensivity of viscosity to solution temperature is higher for AN-AM copolymers synthesized at higher polymerization temperature. The result of thermal analysis shows that the copolymers obtained at higher polymerization temperature are easier to cyclization evidenced from lower initiation temperature. The weight loss behavior changed irregularly with polymerization temperature due to irregular change of liberation heat.     

Morphological and thermal properties of maize fiber composites

Maize stalk has become one of the major sources of fibers from the agricultural residues. Use of these fibers as a reinforcement in the polymer is described in this paper. The present work is focused on establishing the properties such as physical, chemical, morphological structure and thermal properties of maize stalk fiber using different characterization techniques. Simple hand layup method was followed for processing the composite material. Chemical treatments of fibers were carried out to study the interaction of fibers with the matrix. The results revealed that maize fibers can also be used as a traditional fiber as reinforcement in a natural fiber reinforced composite materials.     

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.     

The evaluation of the thermal and mechanical properties of aramid/semi-carbon fibers hybrid composites

In this research work, aramid and semi-carbon fibers (SCFs) were hybridized in the form of interlayer or layer by layer into epoxy matrix by hand lay-up method. Afterward, the effect of hybridization on the thermal and mechanical properties of epoxy composites was characterized by thermal analysis; horizontal burning; tensile and bending tests. Based on the results of the mechanical tests, increasing SCFs to aramid fibers ratio decreased tensile strength, elastic and flexural modulus. But with increasing this ratio to 53 % failure strain reduced, whereas in the ratios of more than 53 %, the failure strain enhanced. The results of thermal analysis curves indicated that there are three stage mass loss at the temperature ranges of 100-220, 270-470 and 500-620 °C. It was also found that with increasing the SCFs to aramid fibers ratio decreased the third-stage of the mass loss. The results of horizontal burning showed that increasing the SCFs to aramid fibers ratio decreased the rate of burning.     

Moisture absorption effect on thermal, dynamic mechanical and mechanical properties of injection-molded short glass-fiber/polyamide 6,6 composites

Polymer composites of polyamide 6,6 reinforced with short glass fiber were prepared by injection molding, conditioned under dry, 50 % relative humidity and wet. Investigations by DSC, DMA and tensile tests were conducted. FLD study showed that more fiber degradation occurred during processing of the composites with higher fiber loading. DSC analysis revealed that the incorporation of glass fiber and moisture into the PA 6,6 matrix resulted in a remarkable decrease in the degree of crystallinity. DMA results revealed the glass transition temperatures were sensitive to moisture absorption and their values moved to a lower temperature upon exposure to moisture. Incorporation of glass fiber into the polyamide 6,6 gave rise to a significant improvement in tensile modulus and tensile strength, while tensile strain was reduced. Exposure to different environments from dry to wet conditions resulted in a decrease in the strength and modulus, while tensile strains decreased.     

Mechanical properties,morphology and dynamic mechanical properties of LGF/TPU/SAN composites

A series of the long glass fiber reinforced thermoplastic polyurethane elastomers and poly (styrene-acrylonitrile) (LGF/TPU/SAN) composites with different contents of long glass fiber were prepared by using self-designed impregnation device. Dynamic mechanical properties of TPU/SAN matrix reinforced with 10, 20 and 30 % by weight long glass fibers have been investigated by using dynamic mechanical thermal analysis (DMA). The results indicated that the content of long glass fiber and scanning frequency had some influence on dynamic mechanical properties and glass transition of LGF/TPU/SAN composites. In addition, the Arrhenius relationship has been used to calculate the activation energy of a-transition of the LGF/TPU/SAN composites. SEM demonstrates the relatively good dispersion of the long glass fiber in the TPU/SAN matrix. In addition, Effects of the content of long glass fiber on mechanical properties of the LGF/TPU/SAN composites are investigated.     

Mechanical,thermal and interfacial properties of green composites from basalt and hybrid woven fabrics

Composites based on pure Basalt and Basalt/Jute fabrics were fabricated. The mechanical properties of the composites such as flexural modulus, tensile modulus and impact strength were measured depending upon weave, fiber contents and resin. Dynamic mechanical analysis of all composites were done. From the results it is found that pure basalt fiber combination maintains higher values in all mechanical tests. Thermo-gravimetric (TG/DTG) composites showed that thermal degradation temperatures of composites shifted to higher temperature regions compared to pure jute fabrics. Addition of basalt fiber improved the thermal stability of the composite considerably. Scanning electron microscopic images of tensile fractured composite samples illustrated that better fiber-matrix interfacial interaction occurred in hybrid composites. The thermal conductivity of composites are also investigated and thermal model is used to check their correlation.     

Effect of inorganic fillers and ammonium polyphosphate on the flammability,thermal stability,and mechanical properties of abaca-fabric/vinyl ester composites

In order to comply with the safety environment requirements, this research is being carried out for reinforcing inorganic additives to improve fire retardancy of composite. In the present study, abaca fabric/vinyl ester (AF/VE) composites were prepared by vacuum assisted resin transfer (VARTM) molding process. For improving flame retardant property of the composites, three different types of halogen free inorganic fillers, i.e. nano-clay (NC), halloysite nanotubes (HNT) and ammonium polyphosphate (APP) were used. The flammability, thermal stability and mechanical properties of composites have been investigated by Horizontal burning test, Thermogravimetric analysis (TGA), tensile, and flexural test respectively. FESEM was used to observe the morphology of the fractured surface of the tensile specimens. Taguchi method was used to optimize the process and minimize the number of experiments for fillers addition. The results showed that the flame retardancy and thermal stability increased with increasing percentage of fillers, but mechanical properties slightly decreased simultaneously.     

Chitosan-filled polypropylene composites: The effect of filler loading and organosolv lignin on mechanical,morphological and thermal properties

In this work, the effect of organosolv lignin on properties of polypropylene (PP)/chitosan composites was investigated. Mechanical and thermal properties of the composites were analyzed by means of ASTM D 638-91, ASTM D 256, thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Tensile strength and elongation at break of the PP composites decreased upon the presence of chitosan filler, but Young’s modulus improved. Impact strength was found to increase with the maximum value at 30 php of filler loading. At a similar loading, treated PP/chitosan composites were found to have higher tensile strength, elongation at break, Young’s modulus as well as impact strength than untreated composites. Furthermore, the presence of organosolv lignin imparted a plasticizing effect. Thermal properties of the treated PP/chitosan composites were better as compared with the untreated PP/chitosan composites; although the chemical treatment did not alter the thermal degradation mechanism. In addition, the obtained results were comparable to results from previous studies. This finding implied that the organosolv lignin could be a potential reagent to replace its synthetic counterpart.     

Experimental study on structure and mechanical properties of hemp/PBTG composites with fiber contents and thermal exposures

Most materials used in daily life are polymeric materials based on petrochemistry. The used polymeric materials can cause land pollution and air pollution after landfill or incineration. In contrast, natural fiber reinforced (NFR) composites are more suitable for the environment, however the reliability in terms of the durability and weatherability of NFR composites is still lacking. Thus, NFR composites require the reliability involved with durability and weatherability. In this work, poly(butylene terephthalate-co-glutarate) (PBTG), with a chemical structure similar to biodegradable PBAT, was used as the matrix in the composites, and hemp fibers were used as the reinforcement. Hemp/PBTG composites were fabricated by stacking hemp-fiberwebs and PBTG films with various fiber contents and thermal exposure times. Characteristics of the composites, such as the morphological structure, chemical structure, tensile properties, compressive properties, flexural properties, and impact strength, were analyzed to obtain the effects of fiber volume fraction and thermal exposure. As a result, hemp/PBTG composites were hardened in proportion to fiber volume fractions, and the hardening behavior of the composites increased tensile strength and flexural strength. However, the hardened structure of the composites decreased the impact strength and compressive strength of the composites. On the other hand, the mechanical properties of hemp/PBTG composites with thermal exposure times, were governed significantly by the brittleness behavior of the resin and the increased crystallinity of hemp fibers. Thus, the hemp fibers contributed to the improvements on structural stability, tensile strength and flexural strength of the hemp/PBTG composites, and increased the thermal durability of the composites with various thermal exposures.     

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.     

Influence of the draw ratio on the mechanical properties and electrical conductivity of nanofilled thermoplastic polyurethane fibers

Electrically conducting textile fibers were produced by wet-spinning under various volume fractions using thermoplastic polyurethane (TPU) as a polymer and carbon black (CB), Ag-powder, multi-walled carbon nanotubes (MWCNTs), which are widely used as electrically conducting nanofillers. After applying the fiber to the heat drawing process at different draw ratios, the filler volume fraction, linear density, breaking to strength, and electrical conductivity according to each draw ratio and volume fraction. In addition, scanning electron microscopy (SEM) images were taken. The breaking to strength of the TPU fiber containing the nanofillers increased with increasing draw ratio. At a draw ratio of 2.5, the breaking to strength of the TPU fiber increased by 105 % for neat-TPU, 88 % for CB, 86 % for Ag-powder, and 127 % for MWCNT compared to the undrawn fiber. The breaking to strength of the TPU fiber containing CB decreased gradually with increasing volume fraction, and in case of Ag-powder, it decreased sharply owing to its specific gravity. The electrical conductivity of the TPU fiber containing CB and Ag-powder decreased with increasing draw ratio, but the electrical conductivity of the TPU fiber containing MWCNT increased rapidly after the addition of 1.34 vol. % or over. The moment when the aggregation of MWCNT occurred and its breaking to strength started to decrease was determined to be the percolation threshold of the electrical conductivity. The heat drawing process of the fiber-form material containing the anisotropic electrical conductivity nanofillers make the percolation threshold of the electrical conductivity and the maximum breaking to strength appear at a lower volume fraction. This is effective in the development of a breaking to strength and electrical conductivity.     

Rheological and thermal properties of masa as related to changes in corn protein during nixtamalization

Traditional nixtamalization process produces a masa (dough) with appropriate cohesiveness and adhesiveness. Masa is considered as a network of solubilized starch polymers with dispersed, uncooked and swollen starch granules, cell fragments, proteins and lipids. In this work, the influence of proteins on the masa viscoelastic behavior was studied in corn kernels under different nixtamalization conditions. Scanning electron microscopy, SDS-PAGE, differential scanning calorimetry and rheological analysis were used to characterize the corn samples. The micrographs showed that the nixtamalization modified the shape of the starch granules and protein bodies, but no changes in appearance were observed when protein was removed. SDS-PAGE showed that corn proteins polymerized during cooking. Lime promoted both calcium–protein and protein–calcium–protein interactions mainly by calcium bridges, which were difficult to disrupt and increased the protein thermo-resistance. In the absence of lime, corn proteins polymerized mainly by disulfide bond cross-linking. Thermal analysis (DSC) indicated that the gelatinization temperature increased in lime-treated samples compared to control samples. Rheological studies showed that the corn protein exhibited greater influence on gel strength by enhancing the elastic character of the samples (G′). These results suggested that polymerized corn proteins stabilized the gel structure, which in consequence influenced the viscoelastic behavior of masa.     

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.