Gamma radiation effect of polymethylvinylphenylsiloxane rubbers under different temperatures

The gamma radiation effect on polymethylvinylphenylsiloxane (PMVPS) rubbers is investigated by irradiation exposure of PMVPS rubbers to a maximum dose of 200 kGy in the temperature range 28–110 °C. Compared with unirradiated PMVPS rubber, the elongation at break of irradiated PMVPS rubber decreases while its elastic modulus increases with the increase of absorbed dose or radiation temperature. DSC, ATR‐FTIR, XPS, and ¹H‐NMR indicate that slight degradation and oxidation reaction occur during the irradiation of PMVPS. Solvent swelling and gel fraction study confirms that the crosslinking density of PMVPS rubbers increases gradually with increasing absorbed dose or radiation temperature. Therefore, radiation‐induced crosslinking of PMVPS is dominant reactions for the chosen dose or temperature range. Furthermore, synergistic effect exists in the high‐temperature radiation process for PMVPS rubbers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45404.     

Polymer melting temperatures and crystallinity at different pressure applied

The present work aims at the experimental investigation of the effect of an increased thermal bonding pressure on the melting point (the so-called Clapeyron effect) of three polymers employed in nonwovens. Namely, this work quantifies the dependence of melting temperature on pressure in these polymers. The following three polymers were used in the present experiments: polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and polypropylene (PP) (all three already received in the form of nonwovens). A simple novel method of measurements of melting points of such polymers under different pressures was proposed and developed. The results revealed: (i) the melting point of PBT nonwovens increased by about 12°C when the applied pressure was increased up to 277.79 atm; (ii) the melting point of the PET nonwovens increased by about 7°C when the applied pressure increased up to 104.86 atm; (iii) the melting point of PP nonwovens increased by about 6°C when the applied pressure was increased up to 104.86 atm. The melting temperature measurements by the present method were also validated through differential scanning calorimetry measurements with the above-mentioned three polymers without applied pressure.     

Epoxy-based composite adhesives with improved lap shear strengths at high temperatures for steel-steel bonded joints

High-performance room temperature-cure epoxy structural adhesives utilizing simplified formulation are developed. The developed structural adhesive consists of diglycidyl ether of bisphenol A (DGEBA) and novolac epoxy blend as a base resin, micrometer-sized silica particles as a reinforcing filler, and triethylenetetramine as a curing agent. The developed ambient temperature-cure epoxy structural adhesive with optimized formulation exhibits outstanding properties including high glass transition temperature of 95°C, high thermal stability with degradation temperature at 5% weight loss of 364°C, exceptionally high rubbery plateau modulus of 320 MPa, good flame-retardant characteristics with limiting oxygen index of 40, and high single lap shear strength for single lap steel-steel bonded joint of 548 MPa at the temperature of 80°C. The silica-filled DGEBA/novolac epoxy composite adhesive is a potential candidate for applying as a structural adhesive for construction with long-term durability.     

The degradation behavior of high-voltage SnO2 based varistors sintered at different temperatures

In this research, for the first time, the stability of SnO₂ based varistor ceramics sintered in the range of 1250–1350 °C against DC-accelerated aging and impulse surge current tests, was systematically studied. Microstructural study of the sintered samples by XRD and FESEM indicated that the sintering temperature only affects densification and grain size, while phase composition remains intact. With the increase of sintering temperature from 1250 °C to 1350 °C, the mean grain size increased from 1.6 to 8 μm. The maximum nonlinear coefficient of 50 and the minimum leakage current density of 1.5 μA/cm² were obtained in the sample sintered at 1300 °C. The breakdown electric field decreased from 800 V/mm to 270 V/mm, when sintering temperature increased from 1250 °C to 1350 °C. The samples sintered at 1250 °C did not show stability against neither of DC-accelerated aging and impulse current tests. The varistors sintered at 1300 °C exhibited the excellent resistance to DC-accelerated aging degradation, while ceramics sintered at 1350 °C showed the best resistance to impulse current degradation.     

Loading rate effects on mechanical properties of polymer composites at ultralow temperatures

E‐glass fibers of 55, 60, and 65 weight percentages were reinforced with epoxy matrix to prepare the laminated composites. They were exposed to ?40, ?60, and ?80°C temperatures for different times. The 3‐piont bend test was conducted on the conditioned samples at those temperatures. Mechanical test was carried out at 2 mm/min and 500 mm/min crosshead speeds. The main emphasis of the investigation was to evaluate the roles of percentage matrix phase and interfacial areas on the interlaminar shear failure mechanism of glass/epoxy composites at ultralow temperatures for different loading speeds. The mechanical performances of the laminated specimens at low temperatures were compared with room temperature property. The loading rate sensitivity of the polymer composites appeared to be inconsistent and contradictory at some points of conditioning time and as well as at a temperature of conditioning. This Phenomenon may be attributed to low‐temperature hardening, matrix cracking, misfit strain due to differential thermal coefficient of the constituent phases, and also to enhanced mechanical keying factor by compressive residual stresses at low temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2289–2292, 2006     

Thermal and photochemical degradation of PPO/HIPS blends

In general, polymer blends show a degradation behavior different from a simple combination of the individual components, making any forecast difficult without experiments. Interactions between polymers can sensibilize or stabilize the blend against degradation. In this work, the thermal and photooxidative degradation of blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) and high impact polystyrene (HIPS) have been studied under accelerated conditions. The extent of degradation was accompanied by infrared spectroscopy (FTIR) and Raman spectroscopy (FT‐Raman) and impact resistance and strain–stress testing followed its influence on the macroscopic properties of the blends. The results showed that HIPS and the blend containing 60 wt % of PPO are more susceptible to thermal and photochemical degradation, while the blends containing 40 and 50 wt % of PPO are more stable. Infrared and Raman spectroscopic analyses showed that the degradation of HIPS and its blends is caused not only by degradation of the polybutadiene phase. Effects of interactions, such as exchange of energy in excited state between the PPO and PS components of the polymeric matrix may also be responsible for the degradation and loss of mechanical properties of the PPO/HIPS blends. The chemical degradation directly affects the mechanical properties of the samples with photodegradation being more harmful than the thermal degradation at 75°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Mechanical and electrical properties of 3Y-TZP/TiSi2 composites sintered at different temperatures

Various amounts of TiSi₂ (30, 40, and 50 wt.%) were added to 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) to fabricate 3Y-TZP/TiSi₂ composites by vacuum sintering. The effects of the TiSi₂ added amount, as well as the sintering temperature on the microstructure, mechanical, and electrical characteristics of the 3Y-TZP/TiSi₂ composites were examined. The sintered samples consisted of three phases: tetragonal (t-ZrO₂), TiSi₂, and reaction product Ti₅Si₃. The maximum bending strength and relative density of the composites, reaching 501.20 MPa and 98.59% respectively, were achieved at a TiSi₂ content of 30 wt.% and sintering temperature of 1500°C. The resistivity of 3Y-TZP/TiSi₂ composites showed a nonlinear decrease with increasing TiSi₂ content. These results indicated that 3Y-TZP/TiSi₂ composites had a typical percolation threshold phenomenon due to the different TiSi₂ content and a conductivity model of 3Y-TZP/TiSi₂ composites at room temperature was founded on the generalized effective medium equation. The resistivity of the composites could optionally adjust between 10² and 10⁻⁴Ω·cm with 30–50 wt.% TiSi₂ under room temperature. Overall, the 3Y-TZP/TiSi₂ composites show great potential for applications in the heat-not-burn tobacco field.     

Effects of medium phases on the thermal degradation of hydrogenated nitrile rubber O‐rings under compression

The degradation of hydrogenated nitrile rubber O‐rings under exposure to either air or hydraulic oil under compression were investigated at elevated temperatures. The physical and chemical changes of the samples aged for various durations were studied by measuring the weight, compression set, tensile strength, elongation at break, crosslinking density, fracture morphology, and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy. The results indicate that the weight decreased with exposure time and temperature and that weight loss was greater in oil. Crosslinking and chain scission both occurred during the aging process. The significant changes in the mechanical properties indicate that more severe degradation occurs in air. The fracture morphologies results show that the fracture surfaces aged in oil become rougher and have more defects. The ATR–FTIR results demonstrate that the hydroxyl groups were formed in air and oil, while carboxyl groups were only generated in air. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45864.     

Fibro‐porous poliglecaprone/polycaprolactone conduits: synergistic effect of composition and in vitro degradation on mechanical properties

Blends of poliglecaprone (PGC) and polycaprolactone (PCL) of varying compositions were electrospun into tubular conduits and their mechanical, morphological, thermal and in vitro degradation properties were evaluated under simulated physiological conditions. Generally, mechanical strength, modulus and hydrophilic nature were enhanced by the addition of PGC to PCL. An in vitro degradation study in phosphate‐buffered saline (pH 7.3) was carried out for up to 1 month to understand the hydrolytic degradation effect on the mechanical properties in both the longitudinal and circumferential directions. Pure PCL and 4:1 PCL/PGC blend scaffolds exhibited considerable elastic stiffening after a 1 month in vitro degradation. Fourier transform infrared spectroscopic and DSC techniques were used to understand the degradation behavior and the changes in structure and crystallinity of the polymeric blends. A 3:1 PCL/PGC blend was concluded to be a judicious blend composition for tubular grafts based on overall results on the mechanical properties and performance after a 1 month in vitro degradation study. © 2014 Society of Chemical Industry     

Toughening effect of CPE on ASA/SAN binary blends at different temperatures

The effect of chlorinated polyethylene (CPE) on the impact toughness of acrylonitrile–styrene–acrylic (ASA) terpolymer/styrene–acrylonitrile copolymer (SAN) binary blends (25/75, w/w) was systematically investigated at three different temperatures (?30 °C, 0 °C, and 23 °C). With the addition of 60 phr CPE, the impact strength increased by 11 times at 23 °C and 10 times at 0 °C. However, the toughening effect was not obvious when the testing temperature was ?30 °C. Since the glass‐transition temperature (T_g) of CPE was about ?18.3 °C as measured with dynamic mechanical analysis tests, the polymeric chains of CPE have been “frozen out” at ?30 °C. As a result, CPE evidently cannot improve the toughness of the blend system. The morphology of impact‐fractured surfaces observed by scanning electron microscopy also confirmed the effect of CPE on the impact toughness of ASA/SAN binary blends. The heat distortion temperature remained almost unchanged, indicating that the improvement in toughness did not sacrifice heat resistance. Furthermore, other mechanical properties were evaluated, and the possible interactions among components of the blends were also analyzed by Fourier transform infrared spectra. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43353.     

Effects of acid treatment at different temperatures on the surface dielectric properties of low‐density polyethylene

The surface dielectric properties of acid‐etched low‐density polyethylene (LDPE) were analysed in the frequency range from 20 Hz to 200 kHz. Samples were treated with various acids for a period of one hour, at temperatures ranging from 20 to 70 °C. After the treatment, the samples were analysed with Fourier transform infrared spectroscopy, revealing chemical and crystallinity changes on the surface, as a direct result of the treatment. The sample surfaces were analysed using atomic force microscopy. The micrographs show that the acid treatment increases the roughness of the samples. Compared to untreated LDPE, the etched samples may exhibit significantly different conductance values at low frequencies. It is also observed that an increase in the acid treatment temperature can result in lower values of conductance and susceptance compared to untreated samples. LDPE films with low value of surface AC conductivity after acid treatment are potentially useful substrates for high‐speed electro‐sensing applications. The presented results indicate that a suitable choice of acid treatment of LDPE can effect surface polarization while preserving low values of surface AC conductivity of the polymer. © 2014 Society of Chemical Industry     

Ionizing radiation as adjuvant for the abiotic degradation of plastic bags containing pro-oxidant additives

The effects of ionizing radiation in promoting the abiotic degradation mechanisms in oxo-degradable plastic bags were studied. Commercial plastic bags, containing pro-oxidant additives, were irradiated with gamma photons and accelerated electrons at doses of 5 and 10 kGy. Then, the irradiated bags were exposed to abiotic degradation, either thermal aging or accelerated weathering. Mechanical and microstructural characterizations were performed to follow the degradation. Plastic bags containing additives did not show important changes in their structure after ionizing radiation and thermal aging. Meanwhile, accelerated weathering combined with gamma photons irradiation produce fragmentation of all the samples after 120 h of degradation. It was concluded that the combination of ionizing radiation and accelerated weathering allows the breakage of polyethylene chains trough accelerating the activation of pro-oxidant additive. Additionally, polyethylene molecules are degraded with pre-treatment of ionizing radiation even if they do not contain the pro-oxidant additive.     

Aging of polyamide 11. Part 3: Multiscale model predicting the mechanical properties after hydrolytic degradation

A holistic general multiscale model of polymer degradation has been applied to predict the mechanical properties of polyamide 11 after the hydrolytic ageing. Results for elastic modulus, tensile strength, and embrittlement threshold have been compared with experimental aging in deoxygenated water at 120°C. For all studied properties the modeled trend is close to the experimental test results confirming hydrolysis induced chain scission and chemicrystalization as the two main mechanisms of property change. This suggests that the multiscale modeling methodology can provide a valuable alternative to accelerated aging tests. The model also indicated that the crystalline phase does play a role in the plastic deformation. Moreover, the mechanical equilibrium between effects of macromolecule degradation and an increased degree of crystallinity has been described. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42792.     

The effect of graphene flake size on the properties of graphene-based polymer composite films

In this work, the role of graphene flake size on the properties of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) composites was studied. Graphene flakes were added to PVDF-HFP using a solution mixing and molding process. By increasing graphene particle size and its concentration in the composites, higher electrical conductivity, in-plane thermal conductivity, and elastic modulus were achieved. Maximum tensile strength was obtained for the composites with average graphene flake size of 2, 5, and 7 μm at graphene concentrations of 10 wt%, 5 wt%, and 20 wt%, respectively. Thick flexible composite films (0.2–0.4 mm) with ultra-high in-plane electrical conductivity (~4500 S/m), in-plane thermal conductivity (~26 W/m/K), and tensile strength (~50 MPa) were obtained for the samples containing the graphene flakes with a larger average particle size of 7 μm. To our knowledge, the first two values are larger than any other values reported in the literature for PVDF-based composites.     

Simulated evaluation of the degradation of hydrophobically associative polymers in the formation

In this work, indoor physical simulation experiments were used to examine the effects of shear, thermal, chemical, and microbial degradation on the properties of the hydrophobic associative polymer AP-P4. It was discovered that the viscosity of the polymer solution generally decreased as the shear time was extended. The larger the shear strength, the lower the solution viscosity. Fitting of the nonlinear equation of solution viscosity with shear time, η = 12,988 t^−1.08. When thermal degradation started, the solution viscosity first started to rise, however, this phase was just a short one. The viscosity of the solution gradually started to decrease as the thermal degradation period grew. In addition, the trends of properties like hydrokinetic radius, hydrophobic connectivity, and hydrolysis essentially followed the same patterns as those of solution viscosity. At the beginning of the degradation process, the viscosity retention of the polymer solution without oxygen is significantly higher than that of the aerobic environment. However, the difference between the two becomes smaller as the degradation time increases. In addition, the AP-P4 had good temperature resistance and aging resistance capabilities when iron ions were present. Finally, it was discovered that AP-P4 had a strong antibacterial effect, which decreased the viscosity brought on by microbial action.     

Studies on a terephthalic acid and dihydroxydiphenyl sulfone liquid crystalline copolymer and its composites with different thermoplastics

A liquid crystalline polymer (LCP) was synthesized by an interfacial polycondensation reaction at room temperature from terephthaloyl chloride and p,p′-dihydroxydiphenyl sulfone. The LCP synthesized was so stable and molecularly rigid that it did not show any phase transition until it degraded at about 320°C. Composites of the LCP with polycarbonate (PC), polystyrene (PS), and sulfonated polystyrene (SPS) were formed by compression molding at a temperature at which the thermoplastic matrix was in the melt state. They were thermally analyzed by differential scanning calorimetry. Tensile specimens were cut from the compression-molded plates, and mechanical tests were performed. The morphology of the material systems was studied by performing scanning electron microscopy analysis on cryogenically fractured specimens. For LCP/PS and LCP/SPS systems, a sharp two-phase morphology was formed, which suggested poor interfacial adhesion. The tensile strength of both systems decreased with LCP addition. The LCP/PC system also revealed a two-phase morphology; however, the interfaces between the LCP domains and the PC matrix were not so well defined, showing better interfacial adhesion than the two previous systems studied. Stronger bonding between the LCP and PC resulted in a significant improvement in the mechanical behavior of PC by LCP addition. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 645–652, 1997     

High‐temperature tensile behavior at different crosshead speeds during loading of glass fiber‐reinforced polymer composites

The present study evaluates on the static tensile behavior of glass fiber reinforced polymer (GFRP) composites at 50% and 70% volume fractions of reinforcement tested at room (25 °C), 70 °C, 90 °C, and 110 °C temperatures with 1, 10, 100, 500, and 1000 mm/min crosshead speeds to investigate the impact of high temperature on the mechanical properties and different dominating failures modes. The experimental results reveal that with increase in crosshead speeds the tensile strength of the composite is increasing. The effect of crosshead speeds and temperature with changing fiber volume fractions affects the GFRP composite. Although both the composite systems are found to be crosshead speed sensitive. Crosshead speed sensitivity seems to be more unpredictable at high temperature and at high crosshead speed. Furthermore, it appears to be more unprecedented nature of fluctuation with high fiber volume fraction. The crucial parameters required during the materials designing in various structural components were evaluated and modelled with the help of Weibull constitutive model. The fractography analyses were done to identify the various dominating failure modes in the GFRP composite. There was no significant change found in the glass transition temperatures (T_g) of both the composite system when exposed to different temperature environments. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44715.     

Effect of coupling agents on the degradation of polypropylene/fly ash composites

Composites containing 50% wt fly ash (sourced from the UK and South Africa) in polypropylene homopolymer (manufacturer stabilized for general purpose use) have been prepared by using batch and continuous methods. The effect of the following coupling agents were investigated on the photo‐ and thermal‐decomposition of the composite materials: Lubrizol Solplus C800 (an unsaturated carboxylic acid), γ‐methacryloxypropyl trimethoxy silane (γ‐MPS), 1,3‐phenylene dimaleimide (BMI), and maleic anhydride‐grafted‐polypropylene (m‐PP). High melt, thermal‐, and photo‐stability was favored when the matrix was coupled to the filler surface by monomeric coupling agents that were expected to adsorb in a close packed layer on the fly ash surface. Further improvements were observed in cases where the coupling agent could also self‐polymerize. m‐PP did not lead to increased stability due to its low adsorption density on the fly ash surface. The relatively high water/acid soluble transition metal ion content of the UK sourced fly ash did not appear to affect stability under the test conditions employed in this study. The South African sourced fly ash had a higher level of quartz and mullite together with a high level of group 1 and 2 metals. The latter in particular may have led to debonding of the coupled interfacial region from the filler surface and possible adsorption of stabilizers on the pristine surface. This resulted in the South African fly ash generally possessing poorer resistance to oxidation than the UK fly ash. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39974.     

The effect of the interface structure of different surface‐modified nano‐SiO2 on the mechanical properties of nylon 66 composites

The nylon 66‐based nanocomposites containing two different surface‐modified and unmodified SiO₂ nanoparticles were prepared by melt compounding. The interface structure formed in different composite system and their influences on material mechanical properties were investigated. The results indicated that the interfacial interactions differed between composite systems. The strong interfacial adhesion helped to increase tensile strength and elastic modulus of composites; whereas, the presence of modification layer in silica surface could enhance the toughness of composites, but the improvement of final material toughness was also correlated with the density of the adhered nylon 66 chains around silica nanoparticles. In addition, the results also indicated that the addition of surface‐modified silica nanoparticles has a distinct influence on the nonisothermal crystallization behavior of the nylon 66 matrix when compared with the unmodified silica nanoparticle. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Sorption characteristic of organic liquid and its effect on the mechanical performance of a PLA‐based plastic

The objective of this article is to assess the mechanical performance of PLA‐based materials under exposure of an organic liquid. In evaluating new opportunities of PLA‐based material, it is important to understand not only the chemical resistance of the material but also the potential route for degradation, which affect the mechanical behavior of the product during its service time. Degradation of PLA material with amount of sorption should be carefully controlled in order to maintain its mechanical performance in response to various loading condition. Distribution of the absorbed liquid within the package is firstly evaluated by identifying the characteristics of the mass transport. Gravimetric analysis is employed to investigate the liquid sorption mechanism and the induced expansion over a particular period. The profile of absorbed liquid content is numerically obtained and verified with the analytic solution. The changes in mechanical performances were investigated by measuring the properties of specimens containing saturated liquid content. It is found that at low temperature, the kinetics of liquid sorption follows the Fick's law but at higher temperature, it showed a deviation from the Fickian curve. The experiment results also confirm progressive decrease of the modulus and strength by increasing of fluid content inside the material. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43250.