Thermal aging of impact-modified polycarbonate

Glassy polymers undergo relatively rapid physical aging just below their glass transition temperatures that can lead to embrittlement of normally tough materials like polycarbonate (PC). One approach for solving the embrittlement problem is to incorporate an impact modifier that can cause toughening when the matrix loses its inherent ductility due to physical aging. The effects of thermal aging below the glass transition temperature of polycarbonate on selected properties of blends of PC with various core-shell impact modifiers have been studied. Observed changes in mechanical properties are related to rubber content, free volume, fracture morphology, discoloration, enthalpy relaxation, glass transition temperature, intrinsic viscosity, and dynamic mechanical behavior. Blend mechanical properties are affected by chemical changes in the impact modifier that occur simultaneous with the physical aging of the PC matrix. The degradation mechanisms involved reduce the effectiveness of the modifier for toughening and also lead to a loss of molecular weight of the PC matrix. Blends containing 10% methacrylated butadiene-styrene (MBS) core-shell impact modifiers give the maximum extension of time to embrittlement at 135°C in air. More thermally stable modifiers are required for further extending the ductile mode of failure for physically aged PC blends.     

Influence of thermal aging on the electrical properties of poly(vinyl chloride)

This article reports on the study of the thermal aging of poly(vinyl chloride) (PVC) used in medium‐ and high‐voltage cables. It is shown that the thermal aging leads to the degradation of the material and to the modification of its electrical properties. The degradation is all the more important and faster as the temperature is high. This degradation is attributed to a progressive evaporation of the plasticizer at the beginning of aging and to a weight loss of stabilizer followed by a change in the color of polymer and a release of hydrochloric acid at more advanced stages of aging. It also results in a crosslinking of the material and a shrinking of samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4728–4733, 2006     

Effect of physical aging on thermal stress development in powder coatings

Thermal stress and physical aging are inherent to thennosetting systems (such as powder coatings) and may affect the coating durability leading to damage such as detachment and cracking. Both phenomena occur principally below the glass transition temperature (T_g) of the coating and affect each other. It is shown that the measurement of stress, as a function of temperature of coatings aged at different temperatures and during various times, represents a simple and interesting way to study these phenomena. The results obtained which show changes in the stress magnitude with aging are explained in terms of stress relaxation and structural recovery. The latter process is especially evident in the T_g region and can prevent the correct determination of the T_g by means of thermal stress measurements. The thermal expansion coefficient and the elastic modulus, two properties directly affecting the thermal stress magnitude were determined separately, and agree well with the proposed interpretation of experimental data. The linear dependence of thermal (compressive) stress on the logarithm of time indicates the possibility of predicting the effect of physical aging.     

Effects of thermal history on impact-modified,high-flow polycarbonate

Miles Inc. recently developed an impact-modified, high-flow polycarbonate to help meet the material requirements for thin wall applications. Melt temperature and heat aging were found to affect its impact strength, yield stress, and dynamic mechanical relaxations. The results are explained in terms of the presence of polycarbonate's high-energy intramolecular conformations formed as a result of intermolecular packing effects during molding, their rearrangement to trans-tans conformations, and the increased interlocking between neighboring chains during heat aging.     

Effect of physical aging on the impact retention and heat distortion temperature of vinyl products

Physical properties of polymers change with time. Exposure of amorphous polymers to high temperature will reduce their free volume, which in turn increases their heat distortion temperature and decreases their impact strength. Heat distortion additives, such as poly(α-methylstyrene-styrene-acrylonitrile) (AMSAN), enhance the glass transition temperature of PVC and help in the impact retention of the polymer by slowing down the aging process. In this paper, physical aging of PVC is explored, effect of annealing time and temperature on the impact strength and HDT is reported, and conclusions regarding the retention of impact resistance upon aging are drawn.     

Effect of thermal aging on the electrical properties of crosslinked polyethylene

This article reports on the effect of thermal aging on the electrical properties of crosslinked polyethylene (XLPE) used in high voltage cables. It was shown that thermal aging modifies the electrical properties of the polymer. The degradation is accelerated when the temperature is increased. This degradation is due to a thermooxidation, followed by a loss of antioxidant, and a change in color of the material. At 80 and 100°C, the antioxidant is practically efficacious during the aging, whereas at 120 and 140°C, it is consumed after 1500 and 1000 h, respectively, which results in an increase in the dielectric losses and a diminution in the volume resistivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effects of physical aging on the thermal and mechanical properties of an epoxy polymer

The effects of free volume on the thermal and mechanical properties of epoxies from diglycidyl ether of bisphenol A (DGEBA) and ethylene diamine (EDA) were investigated. The degree of free volume was controlled by the different thermal history. For fully cured expoxy systems, the density and modulus of both aged and quenched specimens decreased with increasing EDA concentration. However the yield stress of quenched specimens showed a maximum at about equal stoichiometric formulation, while that of aged ones decreased with increasing EDA concentration.     

Low temperature thermal aging of ethylene vinyl alcohol copolymers

The crystallites of semicrystalline polymers formed at low temperatures are subject to partial partial melting and recrystallization resulting in a systematic increase in the size and perfection of the nascent crystallites. Differential scanning calorimetry (DSC) and x-ray studies suggest that ethylene-vinyl alcohol copolymers (EVOH), in particular, may undergo these secondary crystallization processes upon storage at temperatures far below T^m. DSC scans have been run on “as received” and quenched samples; the mole percent of vinyl alcohol in the copolymers studied was 0, 62, 70, 72, 82 and 100 percent. Tests on secondary crystallization kinetics, performed at different temperatures, further confirm the hypothesis of an increased degree of perfection (lamellar thickening) of the bulk crystallites achieved upon long term storage at temperature between T^g and T^m.     

甲基乙烯基硅橡胶/凹凸棒土复合材料的紫外老化性能

以硅烷偶联剂KH 570改性凹凸棒土(AT),制备了甲基乙烯基硅橡胶(MVQ)/AT复合材料,考察了紫外辐射对MVQ/AT复合材料物理机械性能及热性能的影响,并通过扫描电子显微镜表征了复合材料的微观形貌。结果表明,随着辐照时间的延长,MVQ/AT复合材料的邵尔A硬度和拉伸强度先增大后减小,扯断伸长率先减小后增加,热稳定性先提高后下降;MVQ/AT复合材料经紫外辐照后,表面颜色加深并出现裂纹,随着辐照时间的延长,裂纹数量逐渐增加,表面变得粗糙,并且有部分填料暴露在材料表面。     

Irreversible deformation of plasticized and impact-modified poly(vinyl chloride)

Tensile mechanical properties of DOP-plasticized poly(vinyl chloride) (PVC) and methyl methacrylate-butyl acrylate copolymer (MMA-BA) or ethylene vinyl acetate-vinyl chloride copolymer (EVA-VC) modified PVC have been studied. The irreversible deformation processes have been investigated using optical microscopy. Thermal analysis and x-ray diffraction were used to investigate the structure of the PVC blends. The differences in behavior observed for the modified and plasticized PVC are discussed on the basis of their morphology.     

Influence of physical aging on medical plastics properties

Proper design of medical devices requires a thorough understanding of material properties throughout the manufacturing, distribution, and end-use conditions. Widely used amorphous polymers deserve special attention. In this article, we will focus on the physical aging phenomenon. This process affects many important properties of materials. An improved Differential Scanning Calorimetry (DSC) technique was developed to quantify the extent and the kinetics of aging. Consequences of aging were also studied with physical testing and Scanning Electron Microscopy (SEM).     

Effect of molecular structure on the thermal aging properties of flexible urethane foams

A series of flexible urethane foams was formulated from diisocyanate-terminated polyether prepolymers, using both a polyether diol and an ethylenediamine tetraglycol as extenders. The long-term compression set characteristics and the compression deflection properties of these foams were studied. The swelling effect in a solvent, the free isocyanate content, and the role of a carbon black filler on the flexible urethane foam formulation were also evaluated. It was concluded that the total amount of diisocyanate used in the formulation, rather than a variation in the type of isocyanate, has the greatest influence on molecular structure.     

Effect of initiator structure on physical and thermal properties of nylon-6

Nylon-6 is synthesised from ε-caprolactam by an anionic polymerisation method, through a two-step process using sodium metal as a catalyst and diisocyanate-caprolactam block initiator. Two different aliphatic diisocyanates are used. The effects of diisocyanate structure and concentration on percentage cryslallinity, molecular weight, density and thermal properties of nylon are discussed.     

Effect of chromium aging on the structural and thermal properties of chromium polyacrylate

The effects of aging time of Cr(III) solutions on the structural, thermal, magnetic, and morphological properties of chromium polyacrylate complexes were studied. Chromium retention was found to increase with longer aging periods. IR spectra revealed the formation of polychelate structures with noticeable changes on aging. The interaction of multivalent, polynuclear Cr(III) species with the polymer backbone resulted in a decrease in thermal stability for the complexes prepared from olated chromium solutions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 490–493, 2005     

Effect of physical aging and thermal stress on the behavior of polyester/TGIC powder coatings

Physical aging, thermal stress, dynamic mechanical characteristics and thermal expansion of powder coatings from model terephthalic acid (TPA) and isophthalic acid (IPA)-based polyesters (PEs) cross-linked with triglycidyl isocyanurate (TGIC) were studied. Enthalpy relaxation and maximum compressive thermal stress were the properties used to follow the physical aging. The better mechanical properties of TPA-based PE/TGIC powder coatings seem to be due to a combined effect of several properties, i.e., cross-link density (ν_e), thermal expansion coefficient (_F^T) and glass transition temperature (T_g). The higher the values of ν_e, (_F^T) and T_g, the tighter is the coating network, the greater is the coating ability to expand thermally and the slower the physical aging process, respectively, all factors favoring the TPA polyester-based powder coatings.     

Effect of lignin esters on improving the thermal properties of poly(vinyl chloride)

To improve the thermal stability of poly(vinyl chloride) (PVC) and the utilization of lignin (L), different L esters were added to PVC to produce the plates with enhanced thermal stabilities. The properties and structures of the L ester–PVC plates and the properties of the L esters and their mixtures with PVC were analyzed by universal mechanical testing, static thermal stability testing, thermogravimetry–Fourier transform infrared (FTIR) spectroscopy, UV–visible spectroscopy, FTIR spectroscopy, scanning electron microscopy, and differential scanning calorimetry. The results show that L improved the thermal stability of PVC, but the mechanical properties were substantially deteriorated. Proper esterification of L improved the thermal stabilities and mechanical properties of the plates. Noncyclic anhydride acetylated L–PVC plates possessed good static and dynamic thermal stabilities and mechanical properties. The PVC plates incorporated with the L esters with a degree of esterification of around 40% exhibited the best combination properties. Maleated L–PVC plates had good dynamic thermal stability and mechanical properties but poor static thermal stability. The opposite properties were found for succinylated L–PVC plates. The differences in the properties of different L ester–PVC plates were attributed to the different abilities of L esters to capture free radicals, the crosslinking reaction between L esters and PVC, and their compatibility. Different properties of the L esters indicated their different applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47176.