The thermal degradation of aqueous polyurethanes with catalysts of different selectivity

The thermal stability of aqueous polyurethanes has been measured by applying the thermogravimetric analysis. The aqueous polyurethanes (aqPUR) with catalysts of different selectivity have been studied by use of the dynamic method. To obtain degradations of 0.025, 0.05 and 0.10, employing the dynamic method, the heating rates of 0.5, 1, 2, 5 and 10 °C min⁻¹ have been used in the range of 30–500 °C. Using the more selective catalysts in the aqueous polyurethanes the total resulting time of the decomposition has increased at all degradation degrees and at all temperatures. This paper shows that the dynamic method based on the thermogravimetric analysis can be used to assess the thermal stability of the aqueous polyurethanes using the catalysts of different selectivity.     

Halogenation of styrene-butadiene rubber to improve its adhesion to polyurethanes

Halogenation of styrene-butadiene rubbers has been carried out using solutions containing different amounts (0.1-5 wt%) of trichloroisocyanuric acid in butan-2-one. The treated rubber surface showed increased peel strength in joints made with polyurethane adhesive. The effects of chlorination on the rubber surface were studied using scanning electron microscopy, contact angle measurements, and infrared spectroscopy. It was shown that cracks appear in the rubber surface after halogenation, a factor which favours adhesion; the larger the amount of trichloroisocyanuric acid used, the larger the number of cracks. On the other hand, chlorination of the carbon double bond (butadiene) and the formation of carboxylic acid groups seem to be the most important chemical changes in the chlorinated rubber surfaces. Chlorination increases the surface energy of the rubber, although this increase is a function of the rubber composition. In fact, for a simple rubber formulation, the polar component of the surface energy increases for the highest concentrations of chlorine on the rubber surface; but for rubber with a more complicated formulation, the same value of surface energy after chlorination was obtained, independently of the amount of trichloroisocyanuric acid added. A good correlation was found between the contact angle measurements, the infrared spectra, and the peel strength values.     

Variation of thermal stress and dimension of rubber solids upon heating

Gaining an understanding of the dimensional changes and thermal stresses of rubber materials upon heating is very important for the product safety, improved performance and optimum design of the products designed for use under elevated temperatures. The dimensional changes and thermal stresses of pre-deformed natural rubber (NR) and styrene-butadiene rubber (SBR) specimens were investigated and the developed thermal stress was measured at the same conditions as the dimensional change measurement. The dimensions of the stretched rubber specimen initially shrunk at an elevated temperature due to entropic movements, but later increased due to thermal expansion or viscoelastic response. The developed thermal stress increased with increasing pre-strain and temperature because of the entropic nature. The NR specimen showed higher thermal stresses than the SBR specimen.     

Catalytic and thermal degradation of Korean food sludge

Korean food waste sludge was degraded by using a new thermal degradation method. In this system, radish contained waste food sludge as main portion was selected as a standard material. Products of thermal degradation were mainly composed of carbonized solid, small amounts of oil and methane. Total energy production was dependent on the reaction temperature. About 25–32% of solid in the radish was converted to carbonized solid in the thermal degradation of radish at 200°C. The heating values of the carbonized solid and the liquefied heavy oil were 4000–6000 cal/g and about 8000 cal/g respectively. Various catalysts were also examined to improve the carbonized solid used as energy source. Acid clay and MontmorilloniteKSF catalysts showed the best results among the catalysts tested. From the energy balance, this thermal degradation process operated at 200°C was a net energy producer.     

Thermoanalytical and rheological characterization of automotive mineral lubricants after thermal degradation

This work aims to characterize thermal degradation process of automotive mineral lubricants, in relation to its rheological and thermoanalytical properties. Lubricants were degraded at temperatures varying from 150 to 210 °C, and times of 1–48 h. After degradation, oils were characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), rheologic measurements and thermal analysis (TG/DSC). IR and NMR spectra indicated oxidation reaction products. TG curves indicated a decrease in the temperature of decomposition start after degradation. DSC curves indicated a decrease in the peak related to hydrocarbon combustion after degradation. In general, the increase in degradation temperature led to an increase of the lubricants viscosity, besides thixotropy appearance for some samples.     

Characterisation by thermal techniques

Differential thermal analysis and thermogravimetric analysis have been used to study EUROCAT-2 OXIDE (TiO₂–V₂O₅–WO₃). It has been found that water is removed at low temperature, and SO₂ removal and surface reduction (O₂ evolution) take place at high temperature, both for a fresh and a used catalyst.     

Thermal polydimethylsiloxane degradation. Part 2. The degradation mechanisms

The products of the thermal degradation of polydimethylsiloxane (PDMS) are determined by the heating conditions, since two competing mechanisms are involved.Cyclic oligomers are formed in the low degradation temperature range and during slow heating in programmed degradation. This involves molecular splitting of oligomers from loop conformations of the PDMS chain favoured by its flexibility, and assistance on the part of empty silicon d-orbitals.Methane and oligomers are formed in the high temperature range and during fast heating. This shows that homolytic scission of Si-CH₃ also takes place and is followed by hydrogen abstraction.     

The thermal degradation of polystyrene nanocomposite

Nanocomposite formation brings about an enhancement of many properties for a polymer, including enhanced fire retardancy. This study was carried out to determine if the presence of clay causes changes in the degradation pathway of polystyrene. In the case of virgin PS, the degradation pathway is chain scission followed by β-scission (depolymerization), producing styrene monomer, dimer and trimer, through an intra-chain reaction. As the clay loading is increased, the evolved products produced through inter-chain reactions become significant. Due to the barrier effect of the clay layers, the radicals have more opportunity to undergo radical transfer, producing tertiary radicals, and then radical recombination reactions, producing head-to-head structures, and hydrogen abstraction from the condensed phase also occurs. In the presence of clay, the color of solid residues darkens as the clay content increases. It is thought that this color change is caused by the formation of conjugated double bonds in the presence of clay.     

Critical current degradation and delamination crack observation of epoxy-coated REBCO superconducting tapes after thermal cycles in liquid nitrogen

The delamination and critical current (I_c) degradation caused by thermal stress after epoxy impregnation are threats for the application of REBa₂Cu₃O_7-x(REBCO, RE = Rare earth) superconducting magnets. In this work, two types of REBCO tapes were coated by Stycast 2850FT with controlled coating geometries. Critical currents of coated samples after thermal cycles in liquid nitrogen were measured. I_c degradation was found in coated samples with a free no-coating edge, when the surface coating layer was thicker than 1000 μm. It was also found that additional edge coating can help to suppress the I_c degradation. Samples with degraded I_c after thermal cycles showed an obvious delamination phenomenon. The morphology and location of delamination cracks were carefully observed by using focused Ion beam, scanning electron microscope, and transmission electron microscope. Delamination cracks propagated within the REBCO layer and stopped at reaching the Silver/REBCO interface. Simulations by finite element method suggest that delamination cracks are generated by the stress accumulation within the REBCO layer, which could be reduced by a full epoxy coating on both tape surface and edges.     

Kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black

The kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black was investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 5°C/min. The rate parameters were evaluated by the method of Freeman–Carroll. The results show that the thermal degradation of conductive silicone rubber begins at about 350°C and ends at about 600°C. The thermal degradation is multistage, in which zero‐order reactions are principal. The kinetics of the thermal degradation of conductive silicone rubber has relevance to its loading of conductive carbon black. The activation energies are temperature‐sensitive and their sensitivity to temperature becomes weak as temperature increases. In addition, the conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber without any fillers. Also, conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber filled with the same amount of silica. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1548–1554, 2003     

Kinetic model of thermal degradation of polymers for nonisothermal process

A new kinetic model was developed to describe the thermal degradation behavior of polymers. The model was applied to predict the degradation of poly(methyl methacrylate) (PMMA) blended with propyl ester phosphazene (FR). The results showed that the thermal degradation mechanism of pure PMMA was dominated by zero- and first-order reactions. For PMMA blended with FR, the thermal degradation mechanism was dominated by first- and second-order reactions due to the formation of anhydride from the ester groups of PMMA. In addition, the major thermal degradation temperature of blends was greater than pure PMMA. By using our model, the activation energy of the thermal degradation PMMA was calculated to be 180 kJ/mol; this activation energy increased as FR was added to PMMA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1855–1868, 1997     

Kinetic modeling of thermal cracking reactions

This paper provides a kinetics model for thermal cracking of various oils over time frames which correspond to the long term storage at temperatures up to those experienced in an in situ combustion process. The model describes detailed kinetic mechanisms and concentration changes of individual species during the thermal cracking reactions. Also the modeling results are compared with the experimental data to verify their validity.     

聚对苯二甲酸丁二醇酯共聚己二酸丁二醇酯热降解动力学研究

为了研究对比聚对苯二甲酸丁二醇酯共聚己二酸丁二醇酯(PBAT)、聚己二酸丁二醇酯(PBA)以及聚对苯二甲酸丁二醇酯(PBT)的热稳定性,采用热失重(TG)分析法研究了三种树脂的热降解行为.使用Kinssinger法、Flynn-Wall-Ozawa法以及Coats-Redern法对三种树脂的热降解表观活化能以及反应机理...     

Microwave Drying Kinetics of a Thin-Layer Liquorice Root

Liquorice root (LR) (Glycyrrize glabra) is known as a sweetener and medicine plant. Drying kinetics of LR with initial moisture content of 49.5% (wet basis (w.b)) were experimentally investigated in a microwave drying system. The drying experiments were carried out at different drying temperatures (40, 45, 50, and 55°C) and microwave power levels (250, 500 and 750 W). Several models from literature were selected to fit the experimental data. The fit quality of models was evaluated using the coefficient of determination (R²), sum square error (SSE), and root mean square error (RMSE). A new model has been proposed for LR drying in the microwave drying. This new model best describes the experimental data for LRs. The activation energy was calculated to be 46.807 kJ/mol and effective diffusivity ranged from 2.9 × 10^?9 to 5.41 × 10^?9 m²/s, depending on drying temperatures at constant microwave power level.     

Py-GC/MS研究防焦剂CTP的热裂解行为

采用裂解气相色谱/质谱联用法对防焦剂CTP的热裂解行为进行研究,并对部分热裂解产物的质谱碎裂机理进行探讨。结果表明：防焦剂CTP热裂解适宜条件为：温度　300 ℃,时间　0.2 min,方式　单纯瞬间裂解,固体样品直接进样;不同产地产品的裂解产物具有一致性,热稳定性好;裂解产物共10余个,主峰为原分子,次强峰为邻苯二甲酰亚胺。解析了NIST谱库中不包含的主要裂解产物可能的质谱裂解途径;可根据其中环己硫醇、邻苯二甲酰亚胺、二环己基二硫化物3个裂解产物共同判断防焦剂CTP的存在。     

Rubber as additives to lower thermal expansion coefficient of plastics: 1. Morphology and properties

A substantial approach was proposed to design polymer alloys with very low coefficient of linear thermal expansion (CLTE). The large reduction in CLTE is not based on an addition of low-thermal-expansion filler to suppress the bulk expansion, but on the fine control of the polymer alloy's micro-morphology so that the expansion is preferentially toward the thickness direction. In this study, rubber was used as an additive to tune the thermal expansion behavior of various plastics. Although the rubber has a high thermal expansion coefficient, it was found that, when the rubber domains are deformed into microlayers and co-continuous with the plastic matrix, the CLTE of the polymer alloy parallel to the microlayer directions could be reduced to a very low level. Various influencing factors including rubber concentration, viscosity ratio, interfacial adhesion as well as the domain size were investigated.     

Kinetics and parameters affecting degradation of purified natural rubber

Purified natural rubber (PNR) was obtained by treatment of high ammonia NR latex with proteinase enzyme for 24 h, followed by double centrifugation. The PNR was later redispersed into latex form with 0.5% (w/v) sodium dodecyl sulfate. The degradation of PNR was performed in latex form by using a combination of the radical initiator potassium persulfate (K₂S₂O₈) and propanal. The intrinsic viscosity [η] of the degraded rubber or liquid rubber that was obtained depended on various parameters such as the initiator concentration, amount of propanal, dry rubber content, reaction time, and temperature. It was found that the [η] of the rubber can be reduced from 4.31 to 0.19 for the PNR after a 25‐h reaction time using 5% dry rubber content PNR latex, 1 part per hundred rubber (phr) of K₂S₂O₈, and 32 phr of propanal at 80°C. The kinetics of the degradation reaction were investigated. The highest rate constant found was 11.33 × 10^?2 s^?1. The activation energy of the degradation reaction was 76.56 kJ mol^?1. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3546–3555, 2003     

绢云母在丁苯橡胶中的应用

以滁州绢云母为填料,将其改性后制备了改性绢云母/丁苯橡胶(SBR)复合材料,考察了复合材料物理机械性能的影响因素,并通过傅里叶变换红外谱(FTIR)表征了改性绢云母和复合材料。结果表明,在改性剂WD 81质量分数为2.0%、改性温度为90℃、改性时间为25 min以及改性绢云母用量为80份、硫化温度为150℃、硫化时间为12 min的条件下制得的改性绢云母/SBR复合材料的拉伸强度、扯断伸长率、撕裂强度和邵尔A硬度分别达到6.81 MPa、856%、28.04 k N/m和56;改性绢云母/SBR复合材料的官能团发生了加成聚合反应,改性剂起到"桥梁"作用,提高了绢云母对SBR基体的增强作用。     

热降解明胶的研究

报道了明胶热降解反应,并考察了明胶质量分数、降解时间、降解温度、明胶溶液pH值等因素对明胶热降解反应的影响规律。结果表明:热催化是明胶降解的有效方法,较合适的降解条件为明胶质量分数10%,体系pH值7.00,降解温度121℃,降解时间2 h。     

天然橡胶/顺丁橡胶/丁苯橡胶自润滑喷蜡橡胶材料的性能

在天然橡胶(NR)/顺丁橡胶(BR)/丁苯橡胶(SBR)为基体的自润滑喷蜡橡胶材料中加入芥酸酰胺,考察芥酸酰胺作为润滑剂时对NR/BR/SBR自润滑喷蜡橡胶材料的硫化特性、力学性能、门尼黏度、摩擦系数及耐老化性能的影响。结果表明,与未加芥酸酰胺的胶料相比,当芥酸酰胺用量为10份时,胶料转矩减小,焦烧时间和正硫化时间缩短,扯断伸长率从388%增加至523%,拉伸强度降低了21.36%,邵尔A硬度、压缩永久变形分别下降5.56%和8.74%,动、静摩擦系数分别减小23.46%和24.82%,门尼黏度降低20.89%,耐热氧老化性能下降。硫化胶拉伸100%停放5 min后,表面出现明显的白色润滑膜,胶料流动性变好,各组分分散得更均匀,断面更光滑。