Thermal degradation and flammability behavior of polypropylene/clay/carbon nanotube composite systems

This paper reports on the testing and development of a polypropylene (PP) nanocomposite systems with improved flame retardancy. The work utilizes the unique properties of sepiolite nanoclay (Sep) in combination with carbon nanotubes (CNTs) in order to develop an optimized ternary nanocomposite system. Thermogravimetric analysis (TGA) showed significant improvements to the residual char towards the later stages of the thermal ramp. The pyrolysis combustion flow calorimeter (PCFC) was employed to screen the various PP composites with respect to their potential flammability performance. The heat release capacity, which is an indicator of a materials fire hazard, did not show any reduction with the addition of nanofillers using the apparatus standard testing procedure. However, this changed by switching to a lower burn within the PCFC's furnace; this diverted oxygen to the pyrolysing sample. Using the results gained from TGA and the PCFC, the optimized ternary nanocomposite system (10 wt.% Sep + 2 wt.% CNT) was compounded on a larger scale and tested in the cone calorimeter. This showed a significant reduction of 82% in peak heat release rate in comparison to unfilled PP. Comparisons were also made between the testing of these samples in the PCFC and cone calorimeter. The main objectives were to develop a flame‐retardant PP nanocomposite ternary system as well as assessing the PCFC with traditional techniques. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermal hazard analysis of cumene hydroperoxide using calorimetry and spectroscopy

Organic peroxides have been widely used in industries and are known to be self-reactive chemicals. In this paper, thermal and infrared spectroscopic analyses were carried out to obtain a better understanding of the thermally hazardous behavior of cumene hydroperoxide (CHP) with cumene solvent. The temperature and heat flow profiles of different concentrations of CHP at scanning and isothermal conditions were measured with a small scale reaction calorimeter. Furthermore, probe type in situ infrared spectroscopic measurements were performed and the reaction mechanism will be discussed in regards to both energy release and product identification.     

水合烟酸钡的合成、±结构表征和热化学性质

选择烟酸和氢氧化钡作为反应物, 利用室温固相合成方法, 借助于球磨技术, 合成了一种新的化合物——水合烟酸钡. 利用化学分析、元素分析、FTIR和X射线粉末衍射等方法确定了它的组成和结构为Ba(Nic)2·3H2O(s). 利用精密自动绝热热量计直接测定了此化合物在78-400 K温区的摩尔热容. 在热容曲线上出现了一个明显的吸热峰, 通过对热容曲线的解析, 得到了相变过程的峰温、相变焓和相变熵分别为(327.097±1.082) K、(16.793±0.084) kJ·mol-1和(51.340±0.164) J·K-1·mol-1. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 另外, 依据Hess定律, 通过设计合理的热化学循环, 选择体积为100 mL、浓度为0.5 mol·L-1的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计分别测量固相反应的反应物和产物在所选溶剂中的溶解焓, 利用溶解焓确定固相反应的反应焓为⊿rH0m=-(84.12±0.38) kJ·mol-1. 最后, 利用固相反应的反应焓和其它反应物和产物已知的热力学数据计算出水合烟酸钡的标准摩尔生成焓为⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1.     

Thermal properties and combustion behaviors of UV‐cured phosphate triacrylate/star poly(urethane acrylate) oligomer blends

A series of UV‐curable intumescent flame retardant resins was obtained by blending phosphate triacrylate (TAEP) in certain ratios with star poly(urethane acrylate) (SPUA) oligomer. The flammability of the cured films was characterized by limited oxygen index (LOI), UL 94, and the cone calorimeter. The results showed that the cured TAEP/SPUA samples greatly expanded while burning. A distinct synergistic effect was found between TAEP and SPUA. TAEP2 sample showed the highest LOI value (41) among all resins. The cone calorimeter results showed that the peak heat release rates and carbon monoxide yield decreased to the approximate level. The degradation was monitored by thermogravimetric analysis and real‐time Fourier transform infrared spectroscopy. A degradation mechanism is suggested in which the phosphate group in TAEP first degraded to form poly(phosphoric acid)s, which further catalyzed the degradation of the material to form char with emission of carbon dioxide and nitrogen volatiles from SPUA, leading to the formation of expanding char. The morphologic structures of crusts of the formed chars were observed by scanning electron microscopy, demonstrating the synergistic effect between TAEP and SPUA. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydration behavior of C2S and C2AS nanomaterials, synthetized by sol–gel method

Hydration behavior of dicalcium silicate (C₂S) (Cement chemistry nomenclature is used where C=CaO, S=SiO₂, A=Al₂O₃, S=SO₃) and gehlenite (C₂AS), synthesized by sol–gel method was investigated by means of isothermal heat flow calorimeter at different temperatures. These phases were obtained by crystallization processing at different temperatures from their xerogels (nano-crystalline) prepared by the sol–gel method at ambient temperature. The crystallization of C₂S begins below 600°C and it is well crystallized at 900°C. X-ray diffraction patterns reveal that β-C₂S is formed and it remains stable since after slow cooling. The crystallization of C₂AS xerogels starts with the formation of C₂S, then it reacts with alumina to form mineral C₂AS at 1100°C. The effect of hydration temperature upon the hydration reaction of C₂S obtained at 600 and 900°C and C₂AS annealed at 600 and 1100°C was investigated by means of isothermal calorimeter. An increase in the temperature of hydration brought about initial acceleration of all samples, as indicated by the increased magnitude of peak of calorimetric curves. The microstructure of the samples cured at hydrothermal condition after 1 and 7 days has been examined by means of scanning electron microscopy (SEM). Fine crystals of calcium silicate hydrate (C–S–H) were developed in C₂S samples, while C₂AS has been hydrated to form gehlenite hydrate supplemented by C–S–H.     

三聚氰胺的生成焓、热容和熵

通过多种热化学方法研究了三聚氰胺的热力学性质. 首先用氧弹式燃烧热量计测定了三聚氰胺在298.15 K 时的燃烧热, 根据燃烧热结果, 计算出三聚氰胺的标准摩尔燃烧焓和标准摩尔生成焓, 分别为: △cHΘm=(-2455.17±4.65) kJ·mol-1; △fHΘm =(-763.38±5.16) kJ·mol-1. 然后根据键焓与燃烧焓之间的关系, 估算出三聚氰胺中的C≈N(此键介于单键与双键之间)键能为458.30 kJ·mol-1, 此值介于碳氮单键键能和双键键能之间. 通过绝热热量计测定了三聚氰胺从80到385 K的低温热容. 根据热容值, 计算了此温度区间的标准摩尔生成焓, 其与温度呈线性关系. 另外, 三聚氰胺的热稳定性也用热重-差示扫描量热(TG-DSC)法进行了分析, 确定其分解的DSC曲线的峰顶温度为603.37 K.     

A high dynamic range readout unit for a calorimeter

A high dynamic range readout system, consisting of a multi-dynode readout PMT and a VA32 chip, is presented. An LED system is set up to calibrate the relative gains between the dynodes, and the ADC counts per MIPs from dynode 7 are determined under cosmic-ray calibration. A dynamic range from 0.5 MIPs to 1×10⁵ MIPs is achieved.     

A Novel Estimation Method of the Distribution of Carboxyl Groups Within Copolymer Particles Using Isothermal Titration Calorimeter

Summary: A novel quantitative method using isothermal titration calorimeter (ITC) for the estimation of the distribution of carboxyl groups within polymer particles has been proposed. The method has been employed to clarify the difference in the distribution between the particles prepared by batch emulsion copolymerization of styrene and methacrylic acid under inefficient and efficient stirring conditions. At inefficient stirring, monomer was floating as a layer on the aqueous medium, whereas at efficient stirring, the monomer phase was dispersed as droplets. Under inefficient stirring, methacrylic acid (MAA) polymerized faster than styrene (S) due to a slower diffusion rate of S than MAA into the aqueous medium, while under efficient stirring, S and MAA copolymerized at similar rates. ITC measurement showed that under inefficient stirring, the carboxyl groups were distributed mainly in the center of the particles, and their number decreased toward the surface. On the other hand, under efficient stirring, carboxyl groups were distributed homogeneously inside the particle.