Effect of mineral fillers on thermal properties and flammability ofcis-1,4-polyisoprene vulcanizates

The effect of mineral fillers such as Ultrasil VN-3, Ze?O?Sil P-45, Aerosil 200, Frantex 8, Kaolin and precipitated calcium carbonate on the thermal properties sulphur vulcanizates ofcis-1,4-polyisoprene were studied by means of thermal analysis. It was found that the addition of a mineral filler did not change the nature of the thermal processes in isoprene vulcanizates essentially, but it distinctly affected the positions of the peaks recorded in the DTA curves. The mineral fillers affected the temperatures and rates of degradation and destruction of polyisoprene cross-linked with sulphur. The presence of a mineral filler brought about a decrease in the flammability ofcis-1,4-polyisoprene sulphur vulcanizates.     

Effect of carbon black on the thermal properties and flammability of cis-1,4-polyisoprene vulcanizates

The effect of carbon black with various particle sizes and specific surfaces on the thermal properties of the sulphur vulcanizates ofcis-1,4-polyisoprene was studied by means of thermal analysis. It was found that the addition of carbon black does not change the nature of the thermal processes in isoprene rubber vulcanizates essentially, but it distincly affects the positions of the peaks recorded in the DTA curves. The specific surface of carbon black affects the temperature of the first exothermic process and the temperature and rate of destruction of cross-linked polyisoprene. The presence of carbon black brings about a reduction in the flammability ofcis-1,4-polyisoprene vulcanizates. The specific surface of carbon black influences the value of the oxygen index OI.

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Zusammenfassung Mittels Thermoanalyse wurde der Einfluß von Ruß mit unterschiedlicher Partikelgröße und unterschiedlicher spezifischer Oberfläche auf die thermischen Eigenschaften von Schwefelvulkanisaten von cis-1,4-Polyisopren untersucht. Es wurde festgestellt, daß die Zugabe von Ruß die thermischen Vorgänge in Isoprengummivulkanisaten nicht wesentlich verändert, daß jedoch die Lage der in den DTA-Kurven aufgezeichneten Peaks eindeutig beeinflußt wird. Die spezifische Oberfläche von Ruß beeinflußt die Temperatur des ersten exothermen Vorganges sowie Temperatur und Geschwindigkeit von Abbau des vernetzten Polyisoprenes. Die Gegenwart von Ruß führt eine Verminderung der Entflammbarkeit voncis-1,4-Polyisopren-Vulkanisaten herbei. Die spezifische Oberfläche von Ruß beeinflußt den Wert der Sauerstoffzahl.

     

Effect of polyvinylchloride on the properties of rubber vulcanizates

Natural rubber (NR) and styrene-butadiene rubber (SBR) were compounded with polyvinylchloride (PVC). Some physico-mechanical and dielectric properties of resulting rubber vulcanizates were measured. It was found that the addition of PVC to both NR and SBR results in slight decreases in tensile strength and elongation at break but a marked increase in oil-resistance of the vulcanizates. Moreover, the addition of PVC to NR slightly increases both dielectric constant and dielectric losses while the addition of PVC to SBR loaded with 50 phr carbon black (HAF) lowers these parameters. Both rubber blends, especially NR, show a reasonable stability with ageing.     

Effect of nanosilica on thermal oxidative degradation of SBR

The effect of silica content on thermal oxidative stability of styrene–butadiene rubber (SBR)/silica composites has been studied. Morphologies of silica in SBR with different contents are investigated by scanning electron microscopy, which indicates that silica can well disperse in SBR matrix below the content of 40 %, otherwise aggregates or agglomerates will generate. Composites with around 40 % silica content show excellent mechanical properties and retention ratios after aging at 85 °C for 6 days. The values of activation energy (E _a) of pure SBR and its composites are calculated by Kissinger and Flynn–Wall–Ozawa methods based on thermogravimetric (TG) results, which suggests that composite with about 20 % silica has minimum E _a, and composite with 30–40 % silica has maximum E _a. According to TG curves, it is found that silica can suppress the formation of char leading to decline in stability to some extent. On the other side, silica also has positive effect on improving thermal stability of the matrix as filler. Thus, the SBR/silica composites with silica content of 30–40 % can possess both excellent resistance to thermal oxidative degradation and superior mechanical properties.     

Considering factors on determination of microstructures of SBR vulcanizates using pyrolytic analysis

Properties of styrene-butadiene rubbers (SBRs) are depending on their microstructures (contents of 1,4-unit, 1,2-unit, and styrene), but it is hard to determine the microstructures of SBR vulcanizates. Pyrolytic method such as pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been used for microstructures of cured rubbers without pretreatment. Microstructure of SBRs can be estimated using the major pyrolysis products (butadiene, 4-vinylcyclohexene (VCH), and styrene). In this study, considering factors for determination of microstructures of SBR vulcanizates using Py-GC/MS were investigated. The principal considering factors were found to be change of the major pyrolysis products due to radicals formed in carbon backbone and sulfur by dissociation of sulfide crosslinks in SBR vulcanizates. Relative abundances of the major pyrolysis products of raw and cured SBRs were different due to rearrangements of the radicals. Influencing factors on pyrolysis behaviors of SBR vulcanizates were found to be 1,2-unit block, alternating sequence of 1,4- and 1,2-units, styrene-1,4-unit and styrene-1,2-unit sequences, and location of the radicals. Especially, the 1,2-unit block influenced on change of the VCH/butadiene ratio, while the styrene-1,2-unit sequence affected change of the styrene/(butadiene + VCH) one.     

Factors affecting electrical conductivity of carbon black-loaded rubber. II. Effect of concentration and type of carbon black on electrical conductivity of SBR

Effect of the concentration of four types of carbon black, namely, HAF, FEF, ISAF and GPF, on the electrical conductivity of SBR (1502) was studied. The anomalous behavior of conductivity [σ_min in σ(T) curves] becomes more pronounced as we approach a characteristic value of carbon concentration, F₀, at which maximum anomaly occurs; F₀ was found to depend on the type of carbon black. Moreover, the depth of the valley shape of the σ(T) curve increases with the particle size of carbon black used.     

Effect of oil and cured agent content on the structure and properties of thermoplastic vulcanizates

The effect of oil and curing agent content on the mechanical behavior of thermoplastic vulcanizates, based on a polypropylene (PP) and ethylene‐propylene‐diene copolymer (EPDM), was investigated. Mechanical properties such as Young's modulus, stress at 100% elongation and ultimate stress were investigated as a function of blends' composition and phase morphology. Experimental studies show that the Young's modulus of the vulcanizates depends on both PP/EPDM ratio and oil content in the blends; both ultimate strength and stress at 100% elongation increase with curing agent content.     

The effect of the network structure of the thermal properties ofcis-1,4-polyisoprene vulcanizates

The thermal properties ofcis-1,4-polyisoprene and its vulcanizates were investigated by means of thermal analysis and complementary methods. It was found that cross-linking generally increases the thermal stability of this elastomer, though distinct differences between peroxide and sulphur vulcanizates were observed. Polysulphide cross-links cleave readily at elevated temperature, and transform to cross-links of lower sulphidity, mainly disulphide. However, some of them are probably oxidized first to sulphoxides, and further to sulphenic or thiosulphoxylic acids. The products formed involve the ionic decomposition of the peroxides and thereby prevent the autocatalytic thermooxidative destruction ofcis-1,4-polyisoprene.

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Zusammenfassung Es wurden die thermischen Eigenschaften voncis-1,4-Polyisopren und dessen Vulkanisaten untersucht. Dabei wurden die Derivatographie und komplementäre analytische Methoden benutzt. Es wurde festgestellt, dass die Vernetzung im allgemeinen die thermische Stabilität von diesen Elastomeren erhöht, obwohl ein ausgeprägter Unterschied zwischen Peroxid- und Schwefelvulkanisaten beobachtet wurde. Die polysulfidischen Brücken wurden bei erhöhter Temperatur leicht gespalten und verwandeln sich in Brücken, die eine niedrigere Schwefelatomzahl besitzen und zwar hauptsächlich disulfidisch sind. Ein Teil der Schwefelatome wurde jedoch wahrscheínlich unter Bildung von Sulfin- und Thio-Sulfoxysäuren oxydiert. Diese Produkte verursachen ionische Zersetzung von Peroxiden und verhindern auf diese Weise die autokatalytische thermooxidative Zersetzung voncis-1,4-Polyisopren.

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Photocrosslinkable polynorbornene-based block copolymers with enhanced dielectric and thermal properties

Block copolymers poly(endo-N-3,5-bis(trifluoromethyl)biphenyl-norbornene-pyrrolidine)-block-poly(exo-N-(cinnamoyloxyethyl)-7-oxanorborn-5-ene-2,3-dicarboximide) (endo-PTNP-b-exo-PCONBI) and poly(exo-N-3,5-bis(trifluoromethyl)biphenyl-norbornene-pyrrolidine)-block-poly(exo-N-(cinnamoyloxyethyl)-7-oxanorborn-5-ene-2,3-dicarboximide) (exo-PTNP-b-exo-PCONBI) were synthesized by ring-opening metathesis polymerization. The endo- or exo-PTNP served as the high dielectric functional chain, and exo-PCONBI acted as the crosslinking segment. The endo-PTNP-b-exo-PCONBI, in which endo-PTNP has a high content of trans double bond and adopts isotactic configuration, shows a dielectric constant (ε) of 15.5, whereas exo-PTNP-b-exo-PCONBI, in which exo-PTNP has 67% trans double bonds and atactic microstructure, displays relatively low ε of 7.1. The cinnamate groups in exo-PCONBI were crosslinked to form three-dimensional network by cycloaddition reaction under UV irradiation. Exposed to UV-light for 10 min, the cinnamate group in polymer films has a crosslinking conversion of 36%, as determined by UV-Vis absorption measurements. By photocrosslinking, the polymer film has an increased ε of 16.6, a dielectric loss of 0.03, an elevated glass-transition temperature of 137 °C, and an enhanced decomposition temperature of 405 °C, compared to those of polymer films without irradiation.     

Effect of ozone on creep of vulcanizates

In-service secondary creep rates of natural rubber (NR) vulcanizates at ambient temperature are known to be low. However, in tests on thin strips of NR vulcanizates in tension, secondary creep at rates of up to 120%/week were observed. From an examination of the effect of antioxidants, antiozonants, waxes, and specimen thickness it was shown that the anomalous creep was due to ozone attack on the vulcanizate, which only becomes serious in tests on thin strips in tension.     

Influence of the thermal degradation on the dielectric properties of a thermoset

The thermal degradation of an epoxy system consisting of a diglycidyl ether of bisphenol A (DGEBA, n=0) and m-xylylenediamine (m-XDA) was studied by both thermogravimetric analysis (TG) and dielectric analysis (DEA). It has been checked a deviation of the typical behaviour in the Arrhenius plot expected for this kind of systems, owing to the thermal degradation. Both, structural relaxation time and conductivity values, were represented as a function of the mass loss, that allow a relationship to be obtained between characteristic relaxation time and the degree of degradation at the beginning of the degradation process.     

Effect of sunset yellow dye on morphological,optical, dielectric,thermal and mechanical properties of KDP crystal

Herein, we describe the growth and morphology of well-defined dyed crystals of KH₂PO₄ (potassium dihydrogen orthophosphate; KDP) containing organic azo (sunset yellow; SSY) dye in the {1 0 1} & {0 0 1} pyramidal growth sectors. An understanding on selective dye inclusion in various growth sector of host crystal is proposed, which will help in designing novel tailor-made dyed photonic crystals. The structural analysis and the identification of various functional groups present in as grown KDP crystals were carried out using powder XRD, FTIR and Raman studies. Solid state transmittance spectra for dyed KDP crystals displayed three absorption peaks at 230 nm, 311 nm and 477 nm, which were blue shifted for SSY dye in KDP crystal relative to neutral aqueous solution of SSY dye. These blue shifts in the absorption maxima confirm the successful incorporation of sunset yellow dye into the pyramidal growth sectors of dyed KDP crystals. The band around 409 nm in the photoluminescence emission spectrum indicates a violet emission. SSY dye doped KDP crystals showed enhanced dielectric properties and thermal stability as compared to pure KDP crystal. The mechanical strength of the KDP crystals estimated using Vickers microhardness test was found to decrease with the increase in SSY dye doping.     

A relationship between network chain concentration and time dependence of rupture for SBR vulcanizates

The failure properties of crosslinked elastomers are influenced by variables such as the test rate, test temperature, chemical nature of the elastomers, degree of crosslinking, etc. For an elastomer with a fixed degree of crosslinkingthe time dependence of both the stress- and strain-at-break, when determined as a function of the test rate and test speed, can be correlated using a time–temperature shift such as the WLF a_T shift factor. When a similar study is carried out with a sample having a different degree of crosslinking, the time dependence of both the stress- and strain-at-break is shifted along the time scale. It is demonstrated here that the time dependence of failure obtained as a function of the degree of crosslinking can be superposed on a master curve by the use of a time shift factor whose value depends directly on the degree of crosslinking.     

Effect of nano/micro‐mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic‐filled epoxy composite materials have been processed with various percentage additions of SiO₂, Al₂O₃ ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two‐step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron‐size Al₂O₃. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10^?5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano‐size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro‐mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Parylene-AF4: a polymer with exceptional dielectric and thermal properties

[2.2]Paracyclophanes are useful chemical vapor deposition (CVD) precursors of thin film polymers, known as Parylenes. Parylenes are ideally suited for use as conformal coatings in a wide variety of applications, such as in the automotive, medical, electronics, and semiconductor industries. Parylene coatings are inert and transparent and have excellent barrier properties. The bridge-fluorinated 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane (AF4) is the CVD precursor of Parylene-AF4 polymer, which combines a low dielectric constant with high thermal stability, low moisture absorption, and other advantageous properties. With such properties, and because its in vacuo deposition process ensures conformality to microcircuit features and superior submicron gap-filling capability, Parylene-AF4 has considerable promise as an interlayer dielectric for on-chip high-speed semiconductor device interconnection. This paper reviews the synthesis and properties of Parylene-AF4 and its paracyclophane precursor, including a discussion of the importance of the fluorinated bridges, the advantages of the dimeric precursor, and why Parylene-AF4 has the potential to meet the needs of the semiconductor industry with respect to the key properties of a potential interlayer dielectric.     

Phase and state transition effects on dielectric, mechanical, and thermal properties of polyols

The present study investigated the glass transition, crystallisation and melting behaviour of erythritol, xylitol, and glucitol (sorbitol) using dielectric analysis (DEA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Sorbitol and xylitol were plasticised by water and their glass transition temperatures decreased when water content was increased. Erythritol crystallised rapidly, and its water plasticisation behaviour could not be determined. Melting of the crystalline polyols occurred at their specific melting temperatures. Melts of erythritol and xylitol crystallised on recooling and no glass transition was apparent on reheating. Quench cooled sorbitol melt remained amorphous and showed a glass transition on reheating. Glass transition and crystallisation were apparent in the DSC thermogram and the dielectric and the dynamic mechanical spectra of mixtures of amorphous and crystalline xylitol.     

Effect of hydration on the dielectric properties of C-S-H gel

The behavior of water dynamics confined in hydrated calcium silicate hydrate (C-S-H) gel has been investigated using broadband dielectric spectroscopy (BDS; 10(-2)-10(6) Hz) in the low-temperature range (110-250 K). Different water contents in C-S-H gel were explored (from 6 to 15 wt%) where water remains amorphous for all the studied temperatures. Three relaxation processes were found by BDS (labeled 1 to 3 from the fastest to the slowest), two of them reported here for the first time. We show that a strong change in the dielectric relaxation of C-S-H gel occurs with increasing hydration, especially at a hydration level in which a monolayer of water around the basic units of cement materials is predicted by different structural models. Below this hydration level both processes 2 and 3 have an Arrhenius temperature dependence. However, at higher hydration level, a non-Arrhenius behavior temperature dependence for process 3 over the whole accessible temperature range and, a crossover from low-temperature Arrhenius to high-temperature non-Arrhenius behavior for process 2 are observed. Characteristics of these processes will be discussed in this work.     

Preparation and thermal properties of polyquinazolones: Effect of the chemical structure of bisbenzoxazinones on the thermal properties

Four kinds of polyquinazolones were synthesized from 4,4′-diaminodiphenylether and bisbenzoxazinones having different central aromatic nuclei (benzene, biphenyl, benzophenone, diphenylmethane). All the polymers were prepared by solution polycondensation at 190°C at a concentration of 15% solid in m-cresol, and were obtained with intrinsic viscosities in the range of 0.3–0.8 dL/g in 97–98% yield. Their thermal properties were studied by using dynamic thermogravimetry and isothermal weight loss. All the polymers were found to produce high char yields (55–75%) in nitrogen. Oxidative thermal stability of the polymers was dependent on the chemical structure of bisbenzoxazinone and was governed by the stability of the bonds in the quinazolone units. The following order of oxidative thermal stability of the quinazolone units was determined from this study: diphenylmethane < benzophenone < biphenyl < benzene.