The thermal aging of filled polyurethane

Thermal aging and strain endurance experiments on a filled rubber were performed at several temperatures. The rubber was polyurethane (PU) made from hydroxyl-terminated polybutadiene (HTPB) with 4,4′-diphenyl methane disocyanate (MDI). The filler was sodium chloride. The mechanical properties, glass transition temperature, dynamic viscoelasticity, and chemical structures were investigated for filled and unfilled PU under an aging period at 60 and 80°C and 50% relative humidity. We found that at 60°C the chemical structures of the filled and unfilled rubbers had no changes in 30 days during aging. But moisture had some effects on the filled PU and changed its mechanical properties. At 80°C, the chemical structures of the filled and unfilled PU had changed due to the thermal oxidation of polybutadiene in aging. The deterioration was more apparent for the filled rubber than for the unfilled. The prestraining would dewet the filler from the samples and it increased the voids.     

Wood-fiber reinforcement of styrene–maleic anhydride copolymers

Styrene–maleic anhydride (SMA) copolymers containing either 7 or 14% maleic anhydride were filled with either pine flour or dry-process aspen fiber from a medium density fiberboard (MDF) plant. Material properties of the filled and unfilled SMA plastics were compared with those of aspen-fiber-filled and unfilled polystyrene (PS). The fiber-filled SMA composites were equivalent or superior to unfilled SMA in strength, stiffness, and notched Izod impact strength. Filled PS composites outperformed or matched the performance of filled SMA composites in the parameters tested. Unnotched Izod impact strength of filled polymers was generally inferior to that of the unfilled polymers. Water absorption from a 90% relative humidity exposure, a 24-h soak, and a 2-h boil showed mixed results when compared to the unfilled polymers. Dynamic mechanical analysis showed no change in glass transition temperature (T_g) after the addition of filler for either SMA or PS composites. The presence of the anhydride functionality on the polymer backbone did not appear to improve the strength of the composite. No evidence was found for chemical bond formation between the SMA and wood fiber. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1567–1573, 1998     

Effect of crosslink structures on dynamic mechanical properties of natural rubber vulcanizates under different aging conditions

The effects of crosslink structures on the dynamic mechanical properties (DMPs) of unfilled and carbon black N330‐filled natural rubber (NR) vulcanizates cured with conventional (CV), semiefficient (SEV), and efficient (EV) cure systems and having about the same total crosslink densities were investigated before and after aerobic and anaerobic aging at 100°C. The three unfilled NR vulcanizates cured with the CV, SEV, and EV systems had about the same mechanical loss factor (tan δ) values at about 0°C but showed some apparent differences in the tan δ values in the order EV > SEV > CV at relatively high temperatures of 40–80°C before aging. However, N330‐filled NR vulcanizates gave higher tan δ values than the unfilled vulcanizates and showed little effect of the crosslink types on the tan δ at different temperatures over the glass‐transition temperature (T_g) before aging. Aerobic heat aging increased the T_g and tan δ values of the vulcanizates over a wide range of temperatures from ?80 to 90°C that was mainly due to the changes in the total density and types of crosslinks. The unfilled vulcanizates cured with the CV system showed the greatest change in DMP because of their poor resistance to heat aging. Aerobic heat aging of NR vulcanizates caused a more significant change in the DMP than anaerobic heat aging because of the dominant effect of the oxidative degradation during aerobic heat aging on the main‐chain structure, crosslink structures, and DMPs of the vulcanizates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 710–718, 2001     

Comparison of the Mechanical and Thermo-Mechanical Properties of Unfilled and SiC Filled Short Glass Polyester Composites

This paper presents a comparison between particulate filled (SiC particles) and unfilled glass polyester composites on the basis of their mechanical and thermo-mechanical properties. The results show that particulate filled composites have a decreasing trend in mechanical properties when compared to the unfilled glass polyester composites. In particulate filled composites, the tensile and flexural strength of the composites decrease with the addition of 10 wt.-% SiC particles but increase with 20 wt.-% SiC particles. In the case of the unfilled glass polyester composite, the tensile and flexural strength of the composites increase with an increase in the fiber loading. However, higher values of tensile strength and flexural strength of particulate filled glass polyester were found than that of the unfilled glass polyester composite. In the case of thermo-mechanical and thermal properties, the particulate filled composites show better dynamical and thermal properties when compared to the unfilled glass polyester composites. The mechanical and thermal properties (i.e. thermal conductivity) are also calculated using FE modeling (ANSYS software) and the results from this simulation shows good agreement with the experimental results.     

Thermal degradation and ageing behavior of microcomposites of natural rubber,carboxylated styrene butadiene rubber latices,and their blends

The effect of microfillers on the thermal stability of natural rubber (NR), carboxylated styrene butadiene rubber (XSBR) latices, and their 70/30 NR/XSBR blend were studied using thermogravimetric method. Microcomposites of XSBR and their blend were found to be thermally more stable than unfilled samples. The activation energy needed for the degradation of polymer chain was calculated from Coats‐Redfern plot. Activation energy needed for the thermal degradation of filled samples was higher than unfilled system. It indicated the improved thermal stability of the filled samples. The ageing resistance of the micro‐filled samples was evaluated from the mechanical properties of aged samples. The thermal ageing was carried out by keeping the samples in hot air oven for 7 days at 70°C. The mechanical properties such as tensile strength, modulus at 300% elongation, and strain at break were computed. As compared to unfilled samples, micron‐sized fillers reinforced systems exhibited higher ageing resistance. Finally, an investigation was made on the influence of ion‐beam irradiation on microcomposites of NR, XSBR latices, and their 70/30 blend systems using ²⁸Si⁸⁺ performed at 100 MeV. The surface changes of the samples after irradiation were analyzed using X‐ray photoelectron spectroscopy. The results of XPS measurements revealed that the host elements were redistributed without any change in binding energies of C_1s, O_1s, and Si_2p. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of hygrothermal ageing on the monotonic and cyclic loading of glass fiber reinforced polyamide

The properties of short glass fiber reinforced thermoplastic based on polyamide 6 in humid environment are studied. Conditioning was conducted at 90°C. The combined action of water and heat (90°C) affects progressively the mechanical properties. When the injection molded samples were subjected to moisture, decrease in tensile strength and elastic modulus was observed whatever in distilled water or in salt solution. However, there is an enhancement of elongation at break with increasing exposure to humidity. After immersion in water, the fatigue life time is drastically reduced. Scanning electron microscope (SEM) was used in order to examine the fractured samples feature. Results show that water diffuses into the polymer leading to a reduction of the interfacial stress transmissibility. The major contributor of the stiffness loss is the adhesion loss between the fibers and the polymer. POLYM. COMPOS., 35:501–508, 2014. © 2013 Society of Plastics Engineers     

Electron beam modification of filled fluorocarbon rubber

The effect of electron beam irradiation on the properties of carbon black‐, silica‐, and clay‐filled fluorocarbon rubber has been studied over a range of radiation doses, loadings, and nature of the fillers. Compared to the unfilled irradiated rubber, the tensile strength and modulus improve with a decrease in the particle size of the carbon black filler. Similar improvement in these properties is observed with an increase in both the radiation dose and the amount of the filler upto a certain level. The dynamic mechanical analysis reveal an increased glass transition temperature (T_g), a reduced value of the mechanical loss factor at T_g. and an enhanced dynamic storage modulus for the filled samples. The results are explained with the help of sol‐gel analysis and volume fraction of rubber. It is observed that higher reinforcement in the case of the filled vulcanizate is obtained by electron beam modification, as compared to that using the conventional curing system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2016–2025, 2000     

Assessment of crosslink network and network defects of unfilled and filled ethylene‐propylene‐diene terpolymer using solid state nuclear magnetic relaxation spectroscopy

Reinforced rubbers are complex compared to unfilled systems. There are differences in the mechanisms affecting network molecular structure as well as properties of the rubber materials. In this article investigation of crosslink network and untied network defects on a molecular level of unfilled and carbon black filled ethylene‐propylene‐diene terpolymer was carried out using proton solid‐state double‐quantum NMR spectroscopy. The results show that the filled system demonstrates lower cure efficiency in conjunction with more noncoupled network defects than the unfilled one. In addition, the filled system yields the greater spatial heterogeneity because of the localization of the free radicals at the rubber–filler boundary. These strongly influence the mechanical properties of the filled rubber. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44224.     

Indentation deformation and cracking behavior of hydrated aluminoborate glasses

Aluminoborate glasses have recently been found to feature high resistance to crack initiation during indentation due to a highly flexible network structure. In cesium aluminoborate glasses, it has been found that the use of a simple post-treatment, namely aging in a humid atmosphere, can further improve this resistance. To better understand the mechanical properties of this glass family upon humid aging, we here study the effect of aging conditions on the structure and mechanical properties of Li,K,Cs-aluminoborate glasses. As expected, we find that higher humidity and longer aging time cause more pronounced permeation of atmospheric water into the glasses. Due to their denser structure and stronger modifier-oxygen bonds, the humid aging has a relatively smaller effect on the mechanical properties of Li- and K-containing glasses relative to Cs-containing glasses, with the latter achieving an ultrahigh crack resistance. We find that the humid aging leads to the formation of a hydration layer in the Cs-aluminoborate glass surface, with a thickness of around 26 μm upon aging at 23 °C with 40% relative humidity for 7 days. Moreover, a remarkable indentation behavior, that is, the observation of μm-sized shear bands inside the imprint of the Cs-glass upon aging at 60% relative humidity is reported. Taken as a whole, the work provides guidelines for how to control the humid aging rate as a function of relative humidity and temperature to form a hydration layer and thus achieve improved crack resistance in such glasses.     

Reduced indentation recovery temperature at the surface of a crosslinked epoxy coating in humid conditions

Relaxation of surface defects shows that the surface of a crosslinked epoxy system, under normal laboratory conditions, apparently has a softening transition temperature that is approximately 20°C lower than calorimetric measures of T _g in the bulk. Physical aging data here confirms that this transition does resemble a glass transition. This observation is significant for properties that are determined by the surface of a coating. When ambient humidity is such that an epoxy may absorb significant quantities of moisture, it is plasticized, reducing its T _g. When the relaxation of nanoindentations was measured in a humid environment, the value of this softening surface transition temperature was further reduced by 10°C. Thus, the surface properties of a polymer coating, such as wear, durability, friction, will depend not only on the ambient temperature, but also on whether the environment is humid. This is very important when such a coating responds to an environment that changes, e.g., natural weather.     

硫化对炭黑填充SBR体系中多重相互作用的影响

本工作综合运用MDR,RPA以及DMA等表征手段,考察了硫化对炭黑填充SBR体系中多重相互作用的影响。结果表明,炭黑聚集体的絮凝在硫化初期完成。当炭黑含量达到一定值时,炭黑对混炼胶的增强效果优于相应的硫化胶,且应变扫描对混炼胶的增强效果影响较大。Payne效应与炭黑的体积含量间存在一定的对应关系。混炼胶的玻璃化转变温度随炭黑含量的增多升高的幅度大于硫化胶。未填充体系硫化前后的玻璃化转变温度之差大于填充体系。玻璃化转变温度及结合橡胶含量均随炭黑含量的增多而线性增大。     

Accelerated aging of elastomeric composites with vulcanized ground scraps

The aim of this work is to study the effect of thermal aging on the mechanical, dynamic‐mechanical, and chemical properties of SBR (styrene‐butadiene rubber) composites filled with SBR industrial rubber scraps. Eight composites with varying proportions (10–80 phr) of the SBR ground scraps (SBR‐r) were prepared and subjected to accelerated aging in an air‐oven. The composites were evaluated, and the results were compared with a control sample (base formulation with 0 phr of SBR‐r), before and after thermal aging. The accelerated aging led to a decrease in the mechanical properties as a result of an increase in the stiffness of the material, related to an increase in the crosslink density. However, these properties were not affected by the addition of rubber scraps up to 50 phr, either before or after aging. The increase in the glass transition temperature of the composites after aging, measured using dynamic mechanical analysis, confirmed the occurrence of a postcrosslinking process. Fourier transform infrared spectroscopy and crosslink density revealed that the aging mechanism was dependent on the SBR‐r content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparative analysis of ultrasonically devulcanized unfilled SBR,NR, and EPDM rubbers

The comparative study of the continuous ultrasonic devulcanization of various unfilled rubbers [natural rubber, styrene–butadiene rubber (SBR), ethylene–propylene–diene rubber (EPDM)] is carried out by means of a ultrasonic reactor. The power consumption, gel fraction, crosslink density, cure behavior, and physical properties of devulcanized rubbers were measured. The glass transition temperatures of virgin, vulcanized, and devulcanized rubbers were determined in order to characterize the difference in the mobility of rubber molecules for each rubber before and after devulcanization. Thermogravimetric analysis was also used to determine thermal stability of the various rubbers. A unique correlation between gel fraction and crosslink density indicated significant differences in the efficiency of devulcanization of various rubbers. Under certain devulcanization conditions, the mechanical properties of revulcanized SBR and EPDM rubbers were found to improve compared to those of the original rubbers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 434–441, 2003     

改性微晶纤维素的制备及其对填充丁苯橡胶性能的影响II 改性棉纤维素对填充丁苯橡胶性能的影响

研究了微晶纤维素(MCC)和改性微晶纤维素(MMCC)的用量对丁苯橡胶(SBR)硫化胶物理机械性能的影响,以及分别填充20phrMCC和MMCC的SBR复合材料的耐磨性和动态力学性能分析。结果表明,当MCC和MMCC的用量都为20phr时,硫化胶有最大的拉伸强度,分别为15.3MPa和19.0MPa;填充MMCC的SBR复合材料的磨耗体积比填充MCC的降低了41%;填充20phr的MCC和MMCC的SBR具有相似的玻璃化温度。     

反式-1,4-聚异戊二烯的结晶性对丁苯橡胶/反式-1,4-聚异戊二烯共混硫化胶动态力学性能的影响

用动态力学分析仪和差示扫描量热仪研究了丁苯橡胶(SBR)/反式-1,4-聚异戊二烯(TPI)共混硫化胶的动态力学性能和结晶性能。结果表明,SBR与TPI的两相相容性良好。随着TPI用量的增加,SBR/TPI共混硫化胶的玻璃化转变温度向低温方向移动,且损耗因子峰值逐渐降低。用炭黑填充CV体系硫化SBR/TPI共混胶的损耗因子峰值低于相应的未填充胶料;而当TPI晶体熔融后,炭黑填充胶料的损耗因子要大于未填充者。不同硫化体系硫化SBR/TPI共混胶的损耗因子峰值和玻璃化转变温度从大到小的变化依次为CV体系、EV体系和DCP体系。     

Hygrothermal aging of rubber‐modified and mineral‐filled dicyandiamide‐cured DGEBA epoxy resin. II. Dynamic mechanical thermal analysis

The effects of hydration–dehydration cycling on the dynamic mechanical response of a rubber modified, mineral‐filled epoxy resin based on the diglycidyl ether of bisphenol A cured with dicyandiamide are reported. Samples of the resin were aged in both deionized water and 5% w/w NaCl solution at 65 °C. A dynamic mechanical thermal analyzer was used to detect the changes in the mechanical spectrum of the material induced by moisture ingress. Water absorbed at weight fractions up to 4.3% caused plasticization of the polymer matrix, and the measured decrease in the glass transition temperature could be interpreted in terms of the polymer network–diluent theory. Water absorbed at levels >4.3% weight fraction resides in microcavities formed as result of the aging process and did not further affect the dynamic mechanical response of the resin. The dynamic mechanical properties of the material were independent of the previous history of exposure to humidity. In the presence of NaCl, the microcavity growth was prevented and the amount of water absorbed did not exceed 4.1% weight fraction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3477–3485, 2001     

Dynamic birefringence and dynamic mechanical studies on acrylonitrile copolymers

Dynamic birefringence and dynamic mechanical studies have been done on (i) acrylonitrile/methyl acrylate copolymer and (ii) rubber-modified copolymer, in the frequency range of 0.06–5.55 Hz (acrylonitrile/methyl acrylate copolymer only at 0.92 Hz) and temperature range of ?85 to +85°C. These studies were made on a computerized dynamic birefringence apparatus. A comparison of the dynamic birefringence and dynamic mechanical properties in the rubber-modified copolymer reveals a rubber glass transition peak, which is much more pronounced in dynamic birefringence data than in dynamic mechanical data. In addition to the glass transition of the rubber part in the rubber modified copolymer, there is a main transition of the copolymer in the vicinity of 80°C. Before the main transition there is a shoulder in the mechanical and optical loss curves. The reasons for the occurrence of the shoulder are discussed.     

Aromatic liquid transport through filled EPDM/NBR blends

The sorption and diffusion characteristics of 70/30 ethylene propylene diene monomer rubber (EPDM)/acrylonitrile butadiene rubber (NBR) blends loaded with black fillers such as ISAF (intermediate super-abrasion furnace), HAF (high abrasion furnace) and SRF (semi-reinforcing furnace) have been investigated. The penetrants used were benzene, toluene and xylene. Filled samples have been found to show a reduced solvent uptake compared to the unfilled sample for the given blend ratio. The observations have been correlated with the morphology of the systems. Blends loaded with ISAF exhibited the lowest liquid uptake among black filled systems which has been attributed to the better filler reinforcement and enhanced crosslink density of the matrix. The extent of particulate filler reinforcement has been studied by using Kraus theory. The unfilled and filled systems have been found to exhibit non-Fickian transport behaviour. The effect of fillers on the cure and mechanical properties of the blends have also been investigated. Among the black filler loaded systems used, the ISAF mix showed the highest maximum torque value. The improvement in the cure and mechanical properties has been observed to be the highest for ISAF filled samples followed by HAF and SRF filled systems, which is in compliance with the observation from the sorption studies.     

Study on structure and properties of SSBR/SiO2 co‐coagulated rubber and SSBR filled with nanosilica composites

The morphological structure, glass transition, mechanical properties, and dynamic mechanical properties of star‐shaped solution‐polymerized styrene‐butadiene rubber (SSBR) synthesized by a multifunctional organic lithium initiator and SiO₂‐SSBR composite (N‐SSBR) prepared through adding a small amount of nanosilica modified by silane coupling agent to star‐shaped SSBR synthetic solution and co‐coagulating, and their nanocomposites filled with 20 phr nanosilica were investigated, respectively. The results showed that the silica particles were well dispersed with nanosize in N‐SSBR, which glass‐transition temperature (T_g) was 2°C higher than SSBR. N‐SSBR/SiO₂ nanocomposite exhibited lower Payne effect and internal friction loss, higher mechanical properties, and its T_g was 2°C higher than SSBR/SiO₂ nanocomposite. N‐SSBR might promote the dispersion of nanosilica powder in matrix and could be applied to green tire tread materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of organoclay reinforcement on the curing characteristics and technological properties of SBR sulphur vulcanizates

Styrene‐butadiene rubber (SBR) nanocomposites with different organoclay contents (up to 15 phr) were prepared by a melt compounding procedure, followed by a compression‐molding step in which the SBR matrix was sulfur crosslinked. The vulcanizates were characterized in respect to their curing, mechanical and viscoelastic properties, and thermal stability. The optimum cure time decreased with increasing organoclay content. This effect was attributed to the ammonium modifier present in the organoclay, which takes part in the curing reaction acting like an accelerator. The results of mechanical test on the vulcanizates showed that the nanocomposites presented better mechanical properties than unfilled SBR vulcanizate, indicating the nanoreinforcement effect of clay on the mechanical properties of SBR/organoclay nanocomposites. The addition of organoclay did not significantly change the glass transition temperature. However, the heights of tan δ value at the glass transition temperature for the nanocomposites are lower than that of the unfilled SBR. This suggests a strong interaction between the organoclay and the SBR matrix as the molecular relaxation of the latter is hampered. The temperature at which 50% degradation occurs (T₅₀) and the temperature when the degradation rate is maximum (DTG_max) showed an improvement in thermal stability, probably related to the uniform dispersion of organoclay. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010