Morphology and mechanical performance of pregenerated and “in-situ” PP/vectra B composites

Polypropylene/Vectra B blends were obtained at different LCP contents and barrel temperatures by an extrusion-injection process. The wide barrel injection temperature range chosen, from 200 to 300°C, gave rise to blends in which the pregenerated extruded morphology was preserved, partially preserved, or lost. The blends processed at 260 and 300°C showed the usual morphology and properties of “in-situ” composites. The blends injected at 240°C showed the worst properties because of their partially melted and agglomerated morphology. A barrel temperature of 200°C (80°C below the melt temperature of Vectra B) was needed to maintain the pregenerated fibers. These pregenerated composites, without post-extrusion drawing, showed smaller modulus of elasticity and tensile strength than those of the “in-situ” composites, but an increased notched impact strength as a consequence of their less perfectly oriented but more homogeneous morphology.     

Viscosity‐reducing effects of two semiflexible liquid‐crystalline polyesters with different chain rigidities in a matrix of polycarbonate

Two liquid‐crystalline polyesters (LCPs) with different chain rigidities were synthesized and melt‐blended with polycarbonate (PC) at an LCP concentration of 2 wt %. The first LCP (LCP1) was based on hydroxybenzoic acid (HBA), hydroquinone (HQ), sebacic acid (SEA), and suberic acid (SUA) and contained a relatively high concentration of flexible units (SEA and SUA). The other one (LCP2) was based on HBA, hydroxynaphthoic acid, HQ, and SEA and contained a lower concentration of flexible units. LCP2 had a much lower melting point, a higher clearing temperature, and a lower shear viscosity than LCP1. The blending was carried out at 265, 280, and 300°C for both systems. The extent of the viscosity reduction induced by the addition of LCP1 depended on the compounding temperature, and the lowest viscosity was achieved with blending at 280°C. This was attributed to the large interfacial area and interactions between the flexible segments of LCP1 and PC chains at the interface. For PC/LCP2, the viscosity reduction was not significantly dependent on the compounding temperature, and when it was compounded at 280°C, its viscosity was significantly higher than that of PC/LCP1 at high shear rates, even though LCP2 had lower viscosity. A scanning electron microscopy study revealed that, with compounding at 265 and 280°C, LCP2 was poorly dispersed in the PC matrix in comparison with LCP1, and the glass‐transition‐temperature depression caused by the addition of LCP2 was relatively small. This indicated that interfacial interactions in PC/LCP2 were weaker, thereby explaining their different rheological behavior in comparison with PC/LCP1. With compounding at 300°C, the compatibility of both systems improved because of transesterification reactions, but this did not lead to a lower viscosity because of the lack of physical interfacial interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 960–969, 2004     

Effects of injection‐molding processing parameters on acetaldehyde generation and degradation of poly(ethylene terephthalate)

The acetaldehyde (AA) generation behavior of poly(ethylene terephthalate) (PET) has been investigated in terms of its relationship to changes in various processing conditions. A single‐cavity injection‐molding machine was used to prepare preforms in order to relate changes in barrel temperature, screw shear rate, back pressure, cooling time and total residence time to levels of AA generated during processing. Within the temperature range 280–300 °C, a 10 °C rise in processing temperature causes AA production to double. Shear rate increases from 20 to 40 m min^?1 result in 13–21 % increases in AA generation at temperatures from 300 to 280 °C. Increased back pressures from 0 to 200 bar result in AA concentration increases of about 1.2 ppm for each 50 bar pressure increase. The majority of this change is caused by increased polymer residence time. Longer cooling times also increase overall cycle times and result in higher levels of AA generation, at the rate of almost 7 ppm per additional minute at 290 °C processing conditions. Apparent activation energies of 167 kJ mol^?1 were calculated for samples prepared at various shear rates. These results are in agreement with literature values obtained under conditions of static mixing and indicate that shear rate and plastication do not significantly affect reaction mechanisms for AA generation. Copyright © 2005 Society of Chemical Industry     

Performance of long glass fiber‐reinforced polypropylene composites at different injection temperature

Long glass fiber‐reinforced polypropylene composites were prepared using self‐designed impregnation device. Effects of the different injection temperature on mechanical properties, crystallization, thermal, and dynamic mechanical properties of long glass fiber‐reinforced polypropylene composites were discussed. The differential scanning calorimetry (DSC) results indicate that the melting peak temperature of PP/LGF composites gradually reduced, however, the crystallinity of PP/LGF composites gradually increased with increasing injection temperature. Thermo‐gravimetric analyzer (TGA) results demonstrate that with increasing injection temperature, the temperature of the PP/LGF composites melt increased, the viscosity of the PP/LGF composites melt lowered, the mold filling of the PP/LGF composites melt was easy, the shear force of glass fiber was relatively low, which made the residual length of glass fiber in products increase. Dynamic thermal mechanical analyzer (DMA) results show that the storage modulus of PP/LGF composites is the highest while the injection temperature is at 290°C, and the peak value of tan σ of PP /LGF composites at 290°C is minimal, which indicates that the mechanical properties of PP /LGF composites at 290°C is the best. What' more, the injection temperature at 290°C significantly ameliorated “glass fiber rich skin” of products of glass fiber‐reinforced composites. J. VINYL ADDIT. TECHNOL., 24:233–238, 2018. © 2016 Society of Plastics Engineers     

Polyurethane‐infiltrated carbon foams: A coupling of thermal and mechanical properties

The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003     

Processing characteristics of poly(ethylene terephthalate): hydrolytic and thermal degradation

The effects of poly(ethylene terephthalate) (PET) resin moisture content and temperature exposure have been investigated in terms of material changes resulting from the injection moulding process. Two resins with initial carboxyl contents of 10 µeq/g PET and 20 µeq/g PET have been analysed. Preforms processed at different resin moisture contents and processing temperatures of 280, 290 and 300 °C were evaluated in terms of carboxyl end‐group concentration using a titration method. Intrinsic viscosities of the performs were also measured by solution viscosity. Mathematical models describing the relationships of carboxyl end‐group concentration and intrinsic viscosity to the processing conditions were generated from the experimental data. Carboxyl end‐groups formed were compared for both resins and shown to be dependent on initial carboxyl content in the resin. Reducing the initial carboxyl content in the resin has been shown to increase its hydrolytic stability. The hydrolytic effect on the overall molecular weight drop was separated from the thermal/thermal‐oxidative degradation and shown to be dependent on both the processing temperature and the resin moisture content. © 2002 Society of Chemical Industry     

Mechanical performance of ternary in situ polycarbonate/poly(acrylonitrile‐butadiene‐styrene)/liquid crystalline polymer composites

Ternary in situ polycarbonate (PC)/poly(acrylonitrile‐butadiene‐styrene) (ABS)/liquid crystalline polymer(LCP) composites were prepared by injection molding. The LCP used was a versatile Vectra A950, and the matrix of composite specimens was PC/ABS 60/40 by weight. Maleic anhydride (MA) copolymer and solid epoxy resin (bisphenol type‐A) were used as compatibilizers for these composites. The tensile, dynamic mechanical, impact, morphology, and thermal properties of the composites were studied. Tensile tests showed that the tensile strength of the PC/ABS/LCP composite in the longitudinal direction increased markedly with increasing LCP content. However, it decreased slowly with increasing LCP content in the transverse direction. The modulus of this composite in the longitudinal direction appeared to increase considerably with increasing LCP content, whereas the incorporation of LCP into PC/ABS blends had little effect on the modulus in the transverse direction. The impact tests revealed that the Izod impact strength of the composites in both longitudinal and transverse direction decreased with increasing LCP content up to 15 wt %; thereafter it increased slowly with increasing LCP. Dynamic mechanical analyses (DMA) and thermogravimetric measurements showed that the heat resistance and heat stability of the composites tended to increase with increasing LCP content. Scanning electron microscopy observation and DMA measurement indicated that the additions of epoxy and MA copolymer to PC/ABS matrix appeared to enhance the compatibility between the PC and ABS, and between the matrix and LCP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2274–2282, 1999     

Geopolymer reinforced with E‐glass leno weaves

This study explores the viability of fiberglass‐geopolymer composites as an intermediate temperature structural ceramic composite. E‐glass fibers are cheap, readily available, resistant to heat, electricity and chemical attack. Geopolymers are refractory and can be processed at room temperature. However, pure geopolymers have low tensile strength and fracture toughness, as is typical of ceramics. In this work, tensile and flexure properties of metakaolin‐based sodium and potassium geopolymers reinforced with E‐glass leno weaves were measured and the data was analyzed by Weibull statistics. The average tensile and flexural strengths for sodium geopolymer reinforced with E‐glass leno weaves were 39.3 ± 7.2 MPa and 25.6 ± 4.8 MPa, respectively. For potassium geopolymer reinforced with E‐glass leno weaves, the average tensile and flexural strengths were 40.7 ± 9.9 MPa and 15.9 ± 4.0 MPa, respectively. The composites were heat treated for one hour at two temperatures, 300°C and 550°C and their flexure properties were studied at room temperatures. The average flexural strengths for sodium geopolymer reinforced with E‐glass leno weaves were reduced to 6.6 ± 1.0 MPa after heat treatment at 300°C, and 1.2 ± 0.3 MPa after heat treatment at 550°C, respectively. For potassium geopolymer reinforced with E‐glass leno weaves, the average flexural strengths were 6.1 ± 1.5 MPa and 1.3 ± 0.3 MPa after heat treatment at 300°C and 550°C, respectively. SEM and EDS were performed to observe the fiber‐matrix interface. XRD was done to check if the geopolymer was amorphous as expected.     

PTCR characteristics of polycarbonate/nickel‐coated graphite‐based conducting polymeric composites in presence of poly(caprolactone)

The effect of poly(caprolactone) (PCL) on the positive temperature coefficient of resistivity characteristics of polycarbonate (PC)/nickel (Ni)‐coated graphite (40 wt%) composites was investigated. The PTC trip temperature of PC/Ni‐coated graphite composites appeared at 155°C. On addition of PCL to PC/Ni‐coated graphite composites, the PTC trip temperature reduced to 125°C, well below the T_g of the PC (∼147°C), as well as the PC/PCL (∼136°C) blend. It is noteworthy that the observed PTC effect for PC/PCL (8 wt%)/Ni‐coated graphite (40 wt%) composites is highly reproducible during many heating cycles. The coefficient of thermal expansion (CTE) of PC was increased in presence of PCL. Thus, the mismatch in CTE of the PC and Ni‐coated graphite at a temperature well below the T_g of PC was enough to disrupt the continuous network structure that increased the resistivity of the composites. Storage modulus of PC/PCL/Ni‐coated graphite composites was higher than PC/Ni‐coated graphite composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Influence of compatibilizers and processing temperature on microcellular injection‐molded polypropylene/(waste tire powder) composites

Nowadays the economic recycling of waste tires has become a global challenge. The use of waste tire powder as a dispersed elastomeric phase in a polypropylene (PP) matrix offers an interesting opportunity for recycling of waste tire rubber. Compatibilized PP/(waste tire powder) composites are microcellularly processed to create a new class of materials with unique properties. Recent studies have demonstrated the feasibility of developing microcellular structures in PP/waste ground rubber tire (WGRT) composites. Microcellular PP/WGRT composites are prepared by an injection‐molding process using a chemical blowing agent. In this study, cell sizes, cell density, void fraction, and mechanical properties of the composite foams were measured, as well as the shear viscosity of the unfoamed composites. The influence of various compatibilizers and processing temperatures on cell morphology and the mechanical properties of injection‐molded PP/WGRT composites were investigated. It was seen that the addition of maleic anhydride‐grafted styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) increased the shear viscosity of the composites. The void fraction and cell density of the PP/WGRT composites increased with addition of compatibilizers, whereas the average cell sizes decreased. A processing temperature range of 180–195°C gave finer microcellular structure and regular cell distribution. The SEBS‐g‐MA enhanced the elongation properties and acted as an effective compatibilizer in this particular system. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Effects of the processing temperature on the nanostructure and mechanical properties of PCTG‐based nanocomposites

The influence of the processing temperature on both the dispersion level and the mechanical properties of the amorphous copolyester (PCTG)/organoclay (Cloisite® 20A) nanocomposite (NC) is studied in this article. At high processing temperatures, no change in the chemical nature of the matrix was observed, but its molecular weight decreased. Widely dispersed structures were observed by wide angle X‐ray diffraction (WAXD) and transmission electron microscopy whatever the processing temperature might be. Dispersion was greatest for the samples processed at 200°C due to the highest viscosity of these samples and decreased at higher processing temperatures (T_p). These different dispersion levels led to a large modulus increase (71%) after processing at 200°C and to lower ones (about 50%) after processing at 230 and 260°C. The ductility of the NCs decreased at lower processing temperatures. The decrease was attributed to the greater stiffness of the matrix, and was not significant enough to modify the ductile nature of the NCs, which showed clear yield points even at the lowest processing temperature (200°C). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The rheological behavior and dynamic mechanical properties of syndiotactic 1,2‐polybutadiene

The rheological behavior and the dynamic mechanical properties of syndiotactic 1,2‐polybutadiene (sPB) were investigated by a rotational rheometer (MCR‐300) and a dynamic mechanical analyzer (DMA‐242C). Rheological behavior of sPB‐830, a sPB with crystalline degree of 20.1% and syndiotactic content of 65.1%, showed that storage modulus (G′) and loss modulus (G″) decreased, and the zero shear viscosity (η₀) decreased slightly with increasing temperature when measuring temperatures were lower than 160°C. However, G′ and G″ increased at the end region of relaxation curves with increasing temperature and η₀ increased with increasing temperature as the measuring temperatures were higher than 160°C. Furthermore, critical crosslinked reaction temperature was detected at about 160°C for sPB‐830. The crosslinked reaction was not detected when test temperature was lower than 150°C for measuring the dynamic mechanical properties of sample. The relationship between processing temperature and crosslinked reaction was proposed for the sPB‐830 sample. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

High residual mechanical properties at elevated temperatures of bamboo/glass reinforced‐polybenzoxazine hybrid composite

We successfully added bamboo and glass fibers into bisphenol A‐aniline based benzoxazine (BA‐a) resin by hot‐pressing method. In order to improve the interfacial adhesion between bamboo fibers and the matrix, bamboo fibers were pretreated in 6 wt% NaOH solutions for 12 h. The results showed alkali‐treatment had a positive effect on mechanical properties of the composites at both room and elevated temperatures (60°C, 110°C, 160°C, and 210°C). Due to the incorporation of glass fibers, the bamboo/glass reinforced‐polybenzoxazine hybrid composites exhibited highest strength and modulus among all samples and had high residual mechanical properties at elevated temperatures (residual mechanical properties refers to the ratio of strength and modulus of the composites at elevated temperatures to that measured at room temperature). The fractured surface morphologies of the composites were observed by scanning electron microscope. The results showed with the increase of temperature, the debonding and fiber pull‐out became apparent, and the matrix softening could be clearly observed at 210°C. In addition, thermal and thermomechanical properties of neat benzoxazine and the composites were also investigated through thermogravimetric analysis and dynamic mechanical analyzer, respectively. POLYM. ENG. SCI., 59:1818–1829, 2019. © 2019 Society of Plastics Engineers     

Polypropylene nanocomposites with oxo‐degradable pro‐oxidant: Mechanical,thermal, rheological,and photo‐degradation performance

The objective of the study was to generate degradable polypropylene nanocomposites by incorporation of pro‐oxidant and different fillers like silica, silicate, and thermally reduced graphene. Graphene‐based composites exhibited higher crystallinity attributed to better dispersion and high aspect ratio platelets. Graphene composites with 2.5% additive content significantly enhanced the peak degradation temperature to 464°C as compared to 448°C for pure polymer. The processing conditions used for the nanocomposite generation were optimum as a uniform distribution of filler particles (or platelets) was observed in the PP matrix. The tensile modulus of the graphene composite with 2.5% additive content was 80% higher than pure PP, as compared to 60 and 30% for silicate and silica composites, respectively. Similarly, the storage modulus of the graphene nanocomposite with 1% additive content had 30% increment at 40°C as compared to pure PP. PP‐additive blends as well as PP nanocomposites with silica and silicate were observed to attain 100% degree of embrittlement within 6 months of UV exposure at 30°C. Graphene composites, though, had delayed photo‐degradation due to UV absorption by the platelets and high aspect ratio platelets acting as oxygen barrier for PP matrix, but the pro‐oxidant was successful in attaining controlled degradation. POLYM. ENG. SCI., 56:1229–1239, 2016. © 2016 Society of Plastics Engineers     

Mechanical behavior of SiC joints brazed using an active Ag‐Cu‐In‐Ti braze at elevated temperatures

The behavior of SiC ceramic joints brazed with commercially available Incusil ABA (Ag‐32.25Cu‐12.5In‐1.25Ti, in wt.%) was characterized especially with respect to the mechanical performance at temperatures up to 550°C using four‐point bending and torsional shear tests. The failure mechanisms with changing temperature were investigated with the aid of fractography. Additionally, the microstructure of brazed specimens was characterized in detail by high resolution scanning electron microscopy. The test geometry and setup for the high temperature torsional shear test is presented. The change in mechanical behavior of the joints as a function of temperature is shown and discussed. The brazed joints interestingly showed that flexural bending strength was maintained with only a small decrease up to 300°C. Above 300°C, the bending strength decreased much faster. For the first time, this joint system was characterized in torsional shear test at temperatures up to 550°C to achieve the intrinsic shear strength values. Very strong joints were achieved, resulting in failure through the ceramic base materials up to (torsional shear) testing temperatures of 400°C. The results indicate that SiC joints brazed with Incusil ABA exhibit excellent mechanical performance for applications up to 300°C.     

Thermal and dynamic mechanical properties of organic–inorganic hybrid composites of itaconate‐containing poly(butylene succinate) and methacrylate‐substituted polysilsesquioxane

Itaconate‐unit‐containing poly(butylene succinate) (PBSI) was synthesized by the reaction of 1,4‐butanediol, succinic acid, and itaconic acid in a molar ratio of 2.0 : 1.0 : 1.0, and the obtained PBSI was reacted with methacryl‐group‐substituted polysilsesquioxane (ME‐PSQ) in the presence of benzoyl peroxide (BPO) at 130°C to produce PBSI/ME‐PSQ hybrid composites. The thermal and dynamic mechanical properties of the PBSI/ME‐PSQ hybrid composites were investigated in comparison with those of PBSI cured at 130°C in the presence of BPO. As a result, the hybrid composites showed a much higher thermal degradation temperature and storage modulus in the rubbery state than the cured PBSI (C‐PBSI). The thermal degradation temperature and storage modulus of the hybrid composites increased with increasing ME‐PSQ content. The glass‐transition temperature, measured by dynamic mechanical analysis of the hybrid composites, somewhat increased with increasing ME‐PSQ content. However, the glass‐transition temperatures of all the hybrid composites were lower than that of C‐PBSI. Although the IR absorption peak related to C?C groups was not detected for C‐PBSI, some olefinic absorption peaks remained for all the hybrid composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetics of isothermal and non‐isothermal crystallization of poly(butylene terephthalate)/ liquid crystalline polymer blends

The melting behavior and isothermal and non‐isothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/thermotropic liquid crystalline polymer (LCP), Vectra A950 (VA) blends were studied by using differential scanning calorimetry. Isothermal crystallization experiments were performed at crystallization temperatures (T_c), of 190, 195, 200 and 205°C from the melt (300°C) and analyzed based on the Avrami equation. The values of the Avrami exponent indicate that the PBT crystallization process in PBT/VA blends is governed by three‐dimensional morphology growth preceded by heterogeneous nucleation. The overall crystallization rate of PBT in the melt blends is enhanced by the presence of VA. However, the degree of PBT crystallinily remains almost the same. The analysis of the melting behavior of these blends indicates that the stability and the reorganization process of PBT crystals in blends are dependent on the blend compositions and the thermal history. The fold surface interfacial energy of PBT in blends is more modified than in pure PBT. Analysis of the crystallization data shows that crystallization occurs in Regime II across the temperature range 190°C‐205°C. A kinetic treatment based on the combination of Avrami and Ozawa equations, known as Liu's approach, describes the non‐isothermal crystallization. It is observed that at a given cooling rate the VA blending increases the overall crystallization rate of PBT.     

Processability,morphology and mechanical properties of glass fiber reinforced poly(ether sulfone) modified by a liquid crystalline copolyester

Ternary composites based on glass fiber reinforced polyethersulfone (gPES) modified by a liquid crystalline copolyester (R5) were obtained by injection molding at different nozzle temperatures and at LCP contents up to 20%. The blends showed two pure amorphous phases. The ability of R5 to improve processing was seen mainly in the increase in the MFI of the blends on 5% LCP addition, which was more than 75% and 16% with respect to that of pure gPES and PES, respectively. The best processing temperature appeared to be 330°C, as it led to the maximum skin fibrillation and provided both the best small strain and fracture mechanical properties. The blend processed at 330°C with 5% R5 showed the best balance of properties because, besides the highest relative processability increase, it led to maximum values in all mechanical properties measured. This was due to both the overall fibrillation of the skin and to its having the highest ductility.     

Evaluation of interfacial properties and microfailure mechanisms in single fiber‐reinforced epoxy composites at low temperature

In this preliminary study, micromechanical techniques were used to compare the interfacial properties of both carbon and glass fiber composites with two structurally different epoxy matrices (YD‐114 and YDF‐175) at ambient and relatively low temperatures (25°C and −10°C). Tensile modulus of elasticity for both epoxies was higher at lower temperature. Although both fibers exhibited more bimodality at lower temperature than at ambient temperature, glass fiber composites exhibited a statistically greater improvement in tensile strength. This may be attributed to differences in inherent flaws and rigidity. A decrement in stress was observed for YDF‐175 epoxy composites under cyclic loadings at both temperatures, which was attributed to lower interfacial shear strength (IFSS). In contrast to the IFSS of conventional YD‐114 epoxy composites, the IFSS of both the carbon and glass fibers/YDF‐175 epoxy composites studied was higher at the lower temperature. The microfailure pattern observed in microdroplet pullout tests was consistent with the other IFSS results. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

A gradient structure formed in injection‐molded polycarbonate in situ hybrid composites and its corresponding performances

Three polycarbonate (PC) composites that were reinforced, respectively, with liquid crystalline polymer (LCP), glass fibers, and both of them were prepared by a single injection‐molding process. The role of LCP in improving the processibility of the composites was characterized by torque measurement test. The transitions of LCP morphology in two‐ and three‐component composites were investigated by using polarizing optical microscopy and scanning electron microscopy. The micrographs showed a skin–core gradient structure in all three systems investigated, and the addition of glass fiber to the PC/LCP blend affected the morphological transition and content distribution of dispersed LCP phase through the thickness of the injection‐molded samples. These results were correlated well with the measurements of tensile mechanical properties and dynamic mechanical analysis. How to fully use the dispersed LCP phase in PC in situ hybrid composites was discussed for the thickness change of core layer and the heterogeneous distribution of more LCP in the core. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 625–634, 2004