Thermal behavior of vinyl ester resin matrix composites reinforced with alkali‐treated jute fibers

The thermal behavior of vinyl ester resin matrix composites reinforced with jute fibers treated for 2, 4, 6, and 8 h with 5% NaOH was studied with Thermo‐gravimetric analysis and differential scanning calorimetry. The moisture desorption peak shifted to a higher temperature, from 37 to 58.3°C, for all the treated‐fiber composites because of improved wetting of the fibers by the resin and stronger bonding at the interface. The degradation temperature of the vinyl ester resin in the composites was lowered to 410.3°C from that of the neat resin, 418.8°C. The X‐ray diffraction studies showed increased crystallinity of the treated fibers, which affected the enthalpy of the α‐cellulose and hemicellulose degradation. The hemicellulose degradation temperature remained the same (299.7°C) in all the treated‐fiber composites, but the enthalpy associated with the hemicellulose degradation showed an increasing trend in the treated composites with a small increase in the weight loss. This could be attributed to the increased hydrogen bonding between the more accessible ? OH groups of the hemicellulose in the noncrystalline region of the jute fiber and the resin. The degradation temperature of α‐cellulose was lowered from 364.2 to 356.8°C in the treated composites. The enthalpy of α‐cellulose degradation showed a decreasing trend with a lowering of the weight loss. The crystalline regions of the fiber, consisting of closely packed α‐cellulose chains, were bonded with the resin mainly on the surface through hydrogen bonds and became more resistant to thermal degradation; this reduced the weight loss. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 123–129, 2004     

Thermal and nondestructive analysis of high density polyethylene filled with milled salago fiber

Fillers are utilized for different purposes. In plastic industry, fillers are mainly used to extend the bulk of the compound; however, they can also improve physical properties, materials processing, and reduce cycle time of plastics. In this article, high-density polyethylene was filled with untreated and 5% alkaline-treated salago fiber, and thereafter the thermal and nondestructive properties of the composites were investigated. It was found that the chemical treatment of fiber increased the thermal stability and the mean coefficient value of linear thermal expansion of the treated composites as compared to the untreated ones. Moreover, the increase of fiber content in composites increased the crystallinity level while decreased the thermal capacity and melting temperature of the composites. The zinc, calcium, and phosphorus contents were found to be within the industry-acceptable range for elemental contents in polyolefins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47873.     

Thermal and mechanical properties of PES/PTFE composites and nanocomposites

Polyethersulphone/polytetrafluoroethylene (PES/PTFE) nanocomposites and composites were prepared by precipitation of PES into a PTFE latex‐containing nanoparticles. Different samples were obtained by varying the relative ratio between PES and PTFE. The complex crystallization process, discussed within the fractionated crystallization frame, allowed to identify and quantify different dispersion degree of the PTFE nanoparticles within the PES matrix. The different samples were thus divided into nanocomposite and composites. The effect of crystalline PTFE domains on the mobility of PES was investigated and discussed. The dynamic‐mechanical behavior was explained in terms of the particle aggregation state. The mechanical properties of the PES/PTFE composites were found to depend on both the dispersion and the concentration of the PTFE nanoparticles. In the glassy state the stiffness of the materials was found to increase with the dispersion degree, resulting higher for the nanocomposite with respect to composites. On the contrary, in the rubbery state the modulus was found proportional to the PTFE nanoparticles concentration, resulting higher in the composites with respect to the nanocomposite. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3624–3633, 2013     

Energy consumption during dewatering process affected by carboxyl on coal surface

The energy consumption during dewatering and carboxyl concentrations on the surfaces of six different coals were examined. Three stages of dewatering were investigated based on the energy consumption. The water in the spaces between coal particles and large pores, water in progressively smaller capillaries and pores, water clusters around the functional groups, and water directly absorbed by oxygen functional groups were subsequently removed with increasing energy consumption. The moisture present in three forms was significantly affected by carboxyl concentrations. In the first and second stages, the energy consumption at the same residual moisture content was closely related to the carboxyl concentrations. Even at the same ratio of moisture content to carboxyl concentration, energy consumption increased with an increase in carboxyl concentration on coal surface in the second stage.     

Curing kinetics and curing process of phenolic impregnated carbon ablator

Phenolic impregnated carbon ablator (PICA), which is composed of the phenolic resin (PR) and carbon fiber, is of particular interest to researchers in the aerospace field. In this work, PICA was prepared by the double‐stage isothermal heating curing. Then, the curing kinetics of boron‐modified phenolic resin (BPR) was investigated by non‐isothermal differential scanning calorimetry method in order to optimize the curing temperature of BPR. Further, the effect of the heating rate during curing process on the compressive strength of PICA was discussed in detail. The experimental data show that the curing of BPR needs more energy so that the curing temperature of BPR under different condition is higher than that of virgin PR. Notably, with the increasing heating rate during the curing process, the micro‐cracks increase and the compressive strength of PICA decreases. Once the heating rate exceeds a critical value, the micro‐cracks no longer increase and the heating rate has insignificant effect on the compressive strength. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45434.     

Synthesis and characterization of polyethylene glycol acrylate crosslinking copolymer as solid–solid phase change materials

A kind of crosslinking copolymer as solid–solid phase change material (PCM) is synthesized by copolymerization. The scope of PCM applications is often severely limited by their heat stablility and phase transition state. The solid–solid phase change materials we obtained retain basic state during phase change transitions. The crosslinking polymer is heat stable under 300° and the latent heat of crystalline and latent heat of melting is on the average of 120 J/g and 140J/g, respectively. The property of thermal stability and heat storaged is related to crosslinking density of the gel. The property of thermal stability and high latent heat may expand the scope of PCMs applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39755.     

Melt spinning of poly(vinylidene fluoride) fibers and the influence of spinning parameters on β‐phase crystallinity

The effects of melt‐spinning and cold‐drawing parameters on the formation of β‐phase crystallinity in poly(vinylidene fluoride) (PVDF) fibers and ways of increasing such crystallinity were studied. Fibers were melt‐spun with four different melt draw ratios (MDRs) and were subsequently cold‐drawn at different draw ratios (λ). The maximum λ value in cold drawing was dependent on the MDR used in melt spinning. The crystalline structure of the fibers was studied mainly with differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). The results showed that the degree of crystallinity in the fibers was determined by the MDR and that before cold drawing the crystalline structure of the fibers was predominantly in the α form. By cold drawing, α‐phase crystallites could be transformed into the β phase. It was established that, under certain conditions of melt spinning and cold drawing, PVDF fibers of up to 80% crystallinity, mainly in the β form, could be prepared. It was further proposed that fibers spun at a sufficiently high MDR consist to a large extent of extended‐chain crystals, and this greatly affects the melting point of PVDF. Thus, DSC melting‐point data were shown to be insufficient for determining the crystalline phase of PVDF. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nonisothermal crystallization behaviors of silk‐fibroin‐fiber‐reinforced poly(ϵ‐caprolactone) biocomposites

With differential scanning calorimetry measurements, the nonisothermal crystallization of biocomposites of poly(?‐caprolactone) (PCL) reinforced with silk fibroin fiber (SF) was investigated. With the gradual addition of SF, the strengthening of the heterogeneous nucleation reagent effect of SF led to the acceleration of PCL crystallization, and secondary crystallization occurred and became more remarkable with increases in the cooling rate and SF content. Moreover, with the introduction of SF and an increase in the cooling rate, the nucleation and growth mode of the PCL crystalline phase was slightly changed. Because of the confinement of the fiber network structure, the crystallite size of PCL was reduced, the crystallization exothermicity of PCL decreased, and the crystallization activation energy of PCL increased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

PBS/剑麻复合材料制备与性能研究

利用蒸汽爆破预处理剑麻纤维(SESF)作为增强体,通过模压成型制备聚丁二酸丁二醇酯(PBS)/SESF复合材料,研究了SESF质量分数对复合材料力学性能的影响。对比了在剑麻纤维质量分数为30%的条件下,和未经预处理的2种剑麻纤维制得的复合材料的力学性能,并通过扫描电镜(SEM)对试样进行观察分析。结果表明,随着SESF质量分数的增加,复合材料的拉伸强度先增大后减小,在SESF质量分数为30%时达到最大值,比纯PBS的提高了15.5%;弯曲强度和弯曲模量均随剑麻纤维质量分数的增大而提高,其中弯曲强度在SESF质量分数为30%时的比纯PBS的提高了132.5%;断裂伸长率和冲击强度随着SESF质量分数的增加而降低。     

Effect of neutron irradiation on the structural,mechanical, and thermal properties of jute fiber

This article describes the effect of neutron irradiation on jute fiber (Corchorus olitorius). The jute fibers (4.0 tex) were irradiated by fast neutrons with an energy of 4.44 MeV at different fluences ranging from 2 × 10⁹ to 2 × 10¹³ n/cm². An important aspect of neutron irradiation is that the fast neutrons can produce dense ionization at deep levels in the materials. Structural analysis of the raw and irradiated fibers were studied by small‐angle X‐ray scattering (SAXS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy. Thermal analysis carried out on the raw and irradiated fibers showed that the thermal stability of the fibers decreased after irradiation. The mechanical properties of the jute fibers were found to decrease after irradiation. The SAXS study showed that the average periodicity transverse to the layer decreased after irradiation, which may have been due to the shrinkage of cellulosic particles constituting the fiber. The residual compressive stress developed in the fiber after irradiation resulted in a decrease in crystallite size as supported by our XRD analysis. Observation with SEM did not indicate any change produced in the surface morphology of the fiber due to irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of an alkali‐treated grass fiber by thermogravimetric and X‐ray crystallographic analysis

The thermal behavior of grass fiber was characterized by means of thermogravimetric analysis and differential scanning calorimetry analysis. The results proved that the removal of water‐soluble matter improved the thermal behavior of grass fiber over that of unleached fiber, and this was further enhanced by an alkali treatment of the grass fiber. The isothermal weight loss of the grass‐fiber specimens was analyzed at 100, 200, and 300°C for different time periods. Accelerated aging of the grass‐fiber samples was carried out to determine the effect of aging on the tensile strength. Partially delignified grass fiber showed maximum thermal stability. X‐ray diffraction analysis was also performed to verify the composition and to correlate the change in the tensile strength due to the water leaching and alkali treatment. The processing of grass fiber with NaOH and NaClO₂ reduced the amorphous fraction in the fiber sample. This may have been a result of the loss of the amorphous noncellulosic components of the fibers and the degradation of the unordered regions of the grass fiber. However, mercerization of the grass fiber revealed an increase in the amorphous fraction after a certain time exposure, confirming the decrease in the crystallinity. The morphology of the water‐leached and alkali‐treated grass fiber was studied with scanning electron microscopy © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crosslinked poly(vinyl alcohol) and starch composite films: Study of their physicomechanical,thermal, and swelling properties

Crosslinked poly(vinyl alcohol) was blended with 10, 20, 40, and 50 wt % starch by a solution‐casting process. The solution‐cast films were dried, and then their physicomechanical properties including tensile strength, tensile elongation, tensile modulus, tear strength and density, and burst strength and density were tested. Thermal analysis was performed by differential scanning calorimetry. A moisture analysis of the PVA/starch films was performed and their moisture content determined. Also investigated were the films'resistance to solubility in water, 5% acetic acid, 50% ethanol, and sunflower oil and their swelling characteristics in 50% ethanol and sunflower oil. The prepared PVA/starch blends showed significant improvement in tensile modulus and in resistance to solubility in water, 5% acetic acid, and 50% ethanol. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1127–1132, 2007     

Wood particle/high‐density polyethylene composites: Thermal sensitivity and nucleating ability of wood particles

The thermal sensitivity, nucleating ability, and nonisothermal crystallization of high‐density polyethylene (HDPE) with different wood fillers during wood/HDPE melt processing were investigated with thermogravimetric analysis and differential scanning calorimetry. The results showed that the wood degraded at a lower temperature than HDPE. The thermal decomposition behavior was similar across wood species. The most remarkable dissimilarities were observed between wood and bark in the decomposition rate around a processing temperature of 300°C and in the peak temperature location for cellulose degradation. The higher degradation rate for bark was explained by the devolatilization of extractives and the degradation of lignin, which were present in higher amounts in pine bark. The nucleating ability for various wood fillers was evaluated with the crystalline weight fraction, crystal conversion, crystallization half‐time, and crystallization temperature of the HDPE matrix. The nucleation activity improved with the addition of wood particles to the HDPE matrix. However, no effect of wood species on the crystal conversion was found. For composites based on semicrystalline matrix polymers, the crystal conversion may be an important factor in determining the stiffness and fracture behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Loading rate sensitivity of liquid nitrogen conditioned glass fiber reinforced polymeric composites: An emphasis on tensile and thermal responses

Glass fiber reinforced polymeric (GFRP) composites are being accepted as potential materials for ultra‐low temperature applications. The current investigation is to evaluate effect of liquid nitrogen (LN₂) conditioning (for different intervals of time) on the loading rate sensitivity of tensile response of GFRP composites. In order to assess this, tensile tests of the unconditioned and conditioned specimens were carried out at different crosshead speeds viz. 1, 10, 100, 500, and 1000 mm/min. At 1 mm/min crosshead speed, an improvement of 3.33% and 7.3% ultimate tensile strength (UTS) value was observed in case of 0.25 and 1 h conditioned GFRP composites, respectively, as compared to unconditioned GFRP composites. Similarly, the specimens tested at 1000 mm/min show an improvement of 11.39% and 12.02% UTS for 0.25 and 1 h LN₂ conditioned GFRP composites, respectively, as compared to unconditioned GFRP composites. Effect of LN₂ conditioning on crosshead speed sensitivity of modulus and strain at break are also reported. The in‐service temperature of the GFRP composite was measured using temperature modulated differential scanning calorimetry. Furthermore, dynamic mechanical thermal analyzer was used in the temperature range (40–200 °C) to correlate the mechanical and thermomechanical response of the GFRP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45856.     

Effect of SiC whisker on benzoxazine‐epoxy‐phenolic ternary systems: Microwave curing and thermomechanical characteristics

Microwave radiation at 2.45 GHz with variable power input was investigated as a tool to facilitate the curing reaction of benzoxazine‐epoxy‐phenolic molding compound i.e., BEP893. Dielectric filler for microwave coupling was silicon carbide whisker (SiC_w). Factors such as whisker loading and input irradiation power were found to have a profound effect on the microwave heating of the BEP893 particularly on the rate of temperature rise and maximum heating temperature. The SiC_w loading of 10% by weight with the microwave irradiation condition of 300 W for 10 min renders the ultimate curing of the molding compound. Significant reduction in processing time of the microwave cured sample compared with the conventional heat cured sample i.e., 150 min at 200°C using conventional heating is the key benefit of this technique. Mechanical properties of the microwave cured and conventional heat cured samples show similar characteristics with slightly lower T_g in the microwave cured samples. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Industrially viable technique for the preparation of HDPE/fly ash composites at high loading: Thermal,mechanical, and rheological interpretations

This article describes an industrially viable melt blending approach for the preparation of high‐density polyethylene (HDPE)/fly ash composites having high loading of fly ash (FA) (up to 25 wt %). In this approach, solvent was used to enhance the mixing of FA in HDPE matrix. FA coated on the outer surface of HDPE granules using solvent is an economical technique for the incorporation of high loading of FA using conventional twin screw extruder. Herein, the effect of HDPE reinforced with FA on thermal, rheological, and mechanical properties has been investigated. Incorporation of FA in HDPE matrix resulted in higher storage modulus (E′), loss modulus (E″), and complex viscosity (η*) as compared to neat polymer. Tensile and flexural moduli were also found to increase (～47% and ～66%, respectively) with the addition of FA (25 wt %). However, the elongation at break of HDPE reduced as the rigid spherical FA particles do not undergo elongation. The dispersion of FA within the polymer matrix and interaction of FA with HDPE were investigated using scanning electron microscopy. Rheological and mechanical properties of the composites were also correlated with the morphology. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45995.     

Thermal properties of acrylonitrile/itaconic acid polymers in oxidative and nonoxidative atmospheres

Thermal stabilization of polyacrylonitrile (PAN) fibers is an indispensable process in the manufacture of carbon fibers. The effects of acidic comonomers on the thermal properties of PAN have attracted much attention because of their importance in the fibers spinning and heat treatment process. In this study, oxidative and nonoxidative atmospheres are adopted in differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) test to disclose the key effects of oxygen on the thermal properties of PAN/itaconic acid (IA) polymers. The DSC results under oxidative atmosphere are consistence to the reports by previous researchers: the exothermic curves of copolymers containing 0.6 wt % and 1.0 wt % IA exhibit lower initiation temperature and more broaden shapes than that of PAN homopolymer, indicating that IA facilitates both cyclization and oxidation reactions. However, copolymers containing the same content of IA shows no apparent improving effect on the thermal properties under inert atmosphere, which has not been mentioned in the published literature. TGA indicates that oxygen remarkably increases the thermal stability of AN/IA copolymers structure, and will bring high carbon yield in the eventual carbon fibers. The influential mechanisms of oxidative and nonoxidative atmospheres on thermal stabilization reactions of PAN were discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical and film formation behavior from PDMS/NaY zeolite composite membranes

In this study, polydimethylsiloxane (PDMS) and NaY zeolite doped composite membranes were prepared for the films varying from 0 to 15 NaY zeolite wt %. All the membranes were characterized by attenuated total reflectance–Fourier transform infrared (FTIR), X-ray diffraction, scanning electron microscopy, thermogravimetry/differential thermal analysis methods. The FTIR spectral results showed that there is physical interaction existing between the PDMS matrix and NaY zeolite. Additionally, film formation from the pure PDMS and PDMS/NaY composites were investigated by photon transmission technique. Activation energies corresponding to the void closure and the interdiffusion stages were calculated. The NaY zeolite added films led to the significant improvement in the mechanical properties that both the tensile strength and Young's modulus increased three times. Thermal properties of the films were also investigated and the addition of NaY zeolite into the PDMS matrix could significantly improve the thermal stability of the composite membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48549.     

Investigation of the physico‐mechanical properties of electrospun PVDF/cellulose (nano)fibers

The electro‐activity and mechanical properties of PVDF depends mainly on the β‐phase content and degree of crystallinity. In this study, cellulose fibers were used to improve these characteristics. This could be achieved because the hydroxyl groups on cellulose would force the fluorine atoms in PVDF to be in the trans‐conformation, and the cellulose particles could act as nucleation centers. Electrospinning was used to prepare the PVDF/cellulose (nano)fibrous films, and this improved the total crystallinity and the formation of β‐crystals. However, the presence and amount of cellulose in PVDF were found to have little influence on the β‐phase content and on the total crystallinity of PVDF. Improvements in the extent of crystallinity and the β‐phase content were primarily brought about by the chain‐ and crystal orientation as a result of electrospinning. The thermal stability of PVDF in the composites slightly increased with increasing cellulose content in the composites up to 1.0 wt %, while the modulus and tensile strength significantly increased up to the same filler level. The dielectric storage permittivity also increased with increasing cellulose content, but the presence of cellulose had no influence on the dynamics of the γ‐ and β‐relaxations of the PVDF. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43594.