含MDI型TPU热降解探讨

提高TPU的耐热性和热稳定性仍然是一个挑战性的课题，因此了解TPU热老化的进程相当重要。研究表明，软段结构的热氧化在TPU的化学老化过程中起了很重要的角色。研究了MDI型的聚酯、聚醚两种类型TPU的热降解，并且采用多种仪器进行分析，结果显示了聚酯和聚醚不同的降解行为。同时还研究了硬段结构对热降解的影响，在老化过程中，MDI的亚甲基结构转换成了苯酮结构，说明硬段结构在TPU的热老化过程中也起了一个很重要的角色。     

脂肪族聚醚型聚氨酯弹性体热降解机理及热稳定性

采用酯交换缩聚法,以聚四氢呋喃醚二醇（PTMEG）和1,6-六亚甲基二氨基甲酸甲酯（HDU）为原料,以1,4-丁二醇（BDO）为扩链剂,以二丁基氧化锡为催化剂制备脂肪族聚醚型聚氨酯（PU）弹性体。用TGA和FTIR考察聚氨酯弹性体的热降解机理及原料组成对聚氨酯热降解过程的影响。结果表明：聚氨酯弹性体的热降解过程包括两个阶段,分别为硬段（氨基甲酸酯）和软段（聚醚多元醇）的降解,其中硬段（氨基甲酸酯）的降解主要降解产物为碳化二亚胺、CO₂、四氢呋喃及水,软段（聚醚多元醇）的降解主要产物为四氢呋喃和水。随着硬段含量的降低,聚氨酯弹性体初始热降解温度由282℃上升至327℃,聚氨酯弹性体的热稳定性升高。     

核电用EPDM热老化行为研究

通过常规恒温老化箱和热分析仪方法研究了核电常用EPDM的长时和非等温热老化行为.结果表明,EPDM的压缩永久变形和硬度随着老化时间的延长而增大,且热老化程度由外及内逐渐减缓,存在高分子链的氧化、交联与断键等老化特征.短时热分析动力学表明,EPDM的热失重起始反应温度高达200℃,在268℃附近会出现添加剂的优先分解,热...     

热氧老化对氮气气氛下聚碳酸酯热稳定性的影响

采用热空气加速聚碳酸酯(PC)老化的方式进行不同时间下的老化实验,然后在氮气气氛下进行热失重分析,并用Coats-Redfern法和Freeman-Carroll法进行热分解动力学分析。结果表明:老化初期,PC起始分解温度、半失重温度和最大失重温度以及热降解活化能均呈下降趋势;PC的热稳定性下降,主要发生断链和端基脱落;老化后期,PC的起始分解温度、半失重温度和最大失重温度以及热降解活化能又均增大,因PC的交联可使其热稳定性有所提高。     

基于塑料凸轮用尼龙66老化研究及使用寿命预测

采用加速热老化方法,研究了塑料凸轮尼龙66(PA66)的热老化状态和老化机理,通过热重分析(TGA)方法建立了热寿命方程,进行了寿命预测。结果表明:硬度随老化时间的增加逐渐变大,在相同老化时间下,温度越高,硬度值越大;随着老化时间的增加,材料的最大分解温度和失重5%时温度逐渐下降,在相同老化时间下,热老化温度越高,材料的最大分解温度和失重5%时温度降得越快;红外光谱分析表明,随着老化时间的增加,特征峰会发生改变,羧基、羟基和羰基指数随温度升高有增大的趋势;采用TGA热重测试方法,以失重5%时的温度预测材料的使用寿命,得到在30℃、35℃、40℃温度下的使用寿命时间分别为19.81年、12.77年和8.35年。     

热塑性聚氨酯弹性体/氢氧化铝纳米复合材料的热性能分析

以TPU为基体,纳米氢氧化铝(ATH)作为主要改性剂,采用溶液-凝胶法制备ATH/聚醚分散体系,原位聚合法制备TPU/ATH纳米复合材料,并对复合材料的热性能进行分析。DSC分析表明,纳米ATH的添加没有改变TPU微相分离结构,但使TPU软段的玻璃化温度和硬段的分解温度有所提高,说明纳米ATH既存在于聚氨酯大分子软段区又存在于硬段区;TGA-DTA分析表明,纳米ATH改性后的TPU耐热性有所提高,分解温程拓宽约20℃。     

硅烷自然交联聚乙烯热降解研究

对一种一步法硅烷自然交联聚乙烯材料(SCPE419)在自然交联过程中不同时段的热降解行为进行了研究,采用Kissinger动力学处理方法研究其热降解动力学。结果表明:随着自然交联时间的延长,最大热降解速率温度和表观活化能呈逐渐升高的趋势,初始降解温度先降低后升高。该结果说明交联聚乙烯材料中残余少量的引发剂会造成初始降解温度降低,随着网状分子结构的逐渐形成,热稳定性逐渐提高。     

有机硅橡胶热氧老化动力学的评价方法

采用热氧加速老化法,探索了自制的有机硅橡胶在温度变化过程中的各种物理及化学变化的过程,并对其降解过程和使用寿命进行了评估。通过对硅橡胶不同老化时间的热重分析(TGA)测试,得到失重量-温度的曲线及其微熵曲线。利用动态热力分析(DMA)温度扫描的方法,研究了自制的有机硅橡胶在150、175和200℃三个不同温度下不同老化时间的动态热力学性质。研究结果表明:随着老化时间的增加,老化过程由解扣式降解为主导转变为重排式降解为主导。松弛时间τ与温度有关,因此改变温度就可以改变链段运动的松弛时间τ;通过改变温度,可有效地对有机硅橡胶的老化动力学进行评估。选择储能模量作为特性指标,利用Arrhenius速率常数外推模型二步法对该材料进行了使用寿命的评估,得到有机硅橡胶在常温(23℃)的使用寿命约为12年。     

PC／PA1010共混物的热行为

利用热失重、微分热失重和显示扫描量热法研究了聚碳酸酯／尼龙１０１０共混物的热行为和解降解过程。结果表明：共混物在６００℃以下分两步降解，降解温度随尼龙１０１０用量增加有下降趋势；共混物的熔点随尼龙１０１０用量增加而升高。     

核电用聚四氟乙烯密封件老化状态研究及使用寿命预测

选用核电用聚四氟乙烯（PTFE）材料,在不同温度下（315、300、285 ℃）进行高温加速老化试验。通过傅里叶变换红外光谱仪（FTIR）、扫描电子显微镜（SEM）、热失重分析仪（TG）对材料的微观结构、热性能进行了表征分析,然后采用热老化和热失重法建立了2种老化寿命预测模型。结果表明,随着老化时间的延长,PTFE的FTIR谱图出现了明显的红移,表面出现了明显的孔洞,材料的热稳定性和力学性能变差;寿命预测模型显示热失重法与热老化法推算出的寿命预测结果基本一致,并且随着使用温度的增加,误差进一步缩小,这表明热失重法对PTFE材料使用寿命的推算是可靠的,这种简单易行的方法非常适用于PTFE材料。     

Effects of aggregation structure on rheological properties of thermoplastic polyurethanes

The effects of the molecular aggregation structure on the rheological properties of thermoplastic polyurethane (TPU) were investigated. The TPU was composed of poly{(tetramethylene adipate)-co-(hexamethylene adipate)} glycol as the soft segments, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segments. The TPU sheets prepared by injection molding were annealed at various temperatures from 23 to 120 °C to vary the molecular aggregation structure. Glass transition temperature of the soft segment and melting points of the hard segment domains of the TPUs decreased and increased, respectively, with increasing annealing temperature. The results of DSC, solid-state NMR spectroscopy and dynamic viscoelastic measurements revealed that the degree of micro-phase separation of the TPUs becomes stronger with increasing annealing temperature due to the progress of formation of well-organized hard segment domains. The dynamic temperature sweep experiments for molten TPUs revealed that the temperature at critical gel point, which is defined as the temperature at which the dynamic storage modulus coincides with the loss storage modulus, in the cooling process increased with the progress of aggregation of the hard segments in the TPUs observed in the solid state. The uniaxial elongational viscosity measurements showed that TPUs exhibited an obvious strain hardening behavior with strain rate owing to residual hard segment domains at an operating temperature. It was revealed that the formation of well-organized hard segment domains had a profound effect on the rheological properties of TPUs, in particular on their elongational viscosity.     

聚醚型水性聚氨酯热分解动力学的研究

以聚醚N-210为原料,利用丙酮法合成了水性聚氨酯,使用热重分析技术考察了聚醚型水性聚氨酯分别在氮气条件和氧气条件下的热稳定性,并采用"无模式法"研究了在不同气氛氛围下的热分解动力学,同时计算了不同热分解阶段反应的活化能Ea、指前因子A等动力学参数。结果表明:合成的聚醚型水性聚氨酯的热分解过程在氮气条件和氧气条件下均为二阶段过程,第一阶段为硬段链的分解,第二阶段为软段链的分解,同时氧气的存在促进了水性聚氨酯主链上C—C和C—O键的断裂。     

Rheology and extrusion of medical‐grade thermoplastic polyurethane

The selection of operating conditions and geometry for the processing of thermoplastic polyurethane, TPU, is a complicated task. This complication arises from the relatively high melting temperature of the crystalline hard blocks and the oxidative and thermal degradation and crosslinking that occur at temperatures that are relatively close to the melting temperature of the TPU. This article documents the rheology, extrusion, and structure development of a medical‐grade TPU. The medical application requires that the additives commonly utilized in the development of polymeric resins, i.e., stabilizers, antioxidants, and lubricant, should be minimized; the TPU of this study contains no additives. At temperatures 10–20°C lower than the melting temperature of the TPU, the morphology of the hard blocks continues to evolve to generate a reversible increase in elasticity and shear viscosity of the TPU with increasing time. At temperatures greater than the melting temperature, the TPU undergoes degradation and crosslinking reactions, which give rise to a permanent increase in the elasticity and the shear viscosity of the TPU. The ramifications of the degradation and crosslinking at temperatures greater than 200°C and morphology modification upon the continuing evolution of the hard blocks at temperatures less than 200°C on the rheology and processing were investigated.     

Kinetics of the thermal degradation of wax materials obtained from pyrolysis of mixed waste plastics

We did a kinetic analysis of the thermal degradation of wax materials obtained from pyrolysis of mixed waste plastics using the nonisothermal weight loss technique with heating rates of 10, 20, 30 and 40 °C/min. The weight loss data according to degradation temperature were analyzed by using the integral method based on Arrhenius form to obtain the kinetic parameters. To verify the effectiveness of the proposed kinetic analysis method, the experimental values were compared with those of the numerical integration results using kinetic parameters obtained in this work. It was found that the proposed kinetic analysis method gave reliable kinetic parameters of the thermal degradation of wax materials obtained from pyrolysis of mixed waste plastics.     

Seawater degradable thermoplastic polyurethanes

Degradable thermoplastic polyurethane (TPU) elastomers incorporating poly(D ,L ‐lactide‐co‐glycolide) (PLGA) were synthesized and characterized. The soft segments consisted of a mixture of poly(butylene adipate) (PBA) and PLGA with PBA/PLGA ratios of 100/0, 75/25, and 50/50 wt %. Two PLGA polyesters were used. BD‐PLGA was initiated from butanediol; whereas BHMBA‐PLGA was initiated from 2,2‐bis‐(hydroxymethyl)butanoic acid. The hard segments consisted of dicyclohexylmethane‐4,4′‐diisocyanate (H₁₂MDI) and 1,4‐butanediol (BD). The hard segment content, expressed as the weight ratio of BD to polyol used in the TPU formulation, was set either at 8 or 12% (31.2 or 38.1% hard segment by weight, respectively). In all cases initial [NCO]/[OH] ratio was 1.03. The tensile modulus of the TPUs ranged from 9 to 131 MPa and ultimate strains ranged from 100 to 750%. DMA was used to probe the thermomechanical transitions of the TPUs and indicated useful application temperatures from well below zero up to 60–80°C depending on the formulation. Hydrolytic degradation of the TPUs was tested in seawater at 37°C. All of the PLGA‐containing TPUs showed enhanced degradation compared to those with only PBA as the soft segment. The latter compositions remained essentially unchanged throughout the test while the PLGA‐containing TPUs lost as much as 45% of their initial mass in 153 days. Molecular weights of TPUs containing degradable polyols were lower than those derived from 100% PBA polyol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

TODI型热塑性聚氨酯弹性体的制备与性能研究

简单介绍了TODI型热塑性聚氨酯弹性体(TPU)的合成工艺、软段种类、硬段含量、R值等对其性能的影响,并与MDI型TPU的动态力学性能作对比.结果表明,使用预聚体法工艺制备的聚ε-己内酯(PCL)型TPU具有良好性能,硬段含量和R值在一定范围内的提高可提高材料的力学性能,与MDI型TPU相比,高温下TODI型TPU储能...     

Strategy for kinetic parameter estimation—Thermal degradation of polyurethane elastomers

The kinetics of the thermal degradation of polyurethane (PU) elastomers based on poly(ether polyol) soft segments and an aromatic type of diisocyanate were investigated by thermogravimetric analysis (TGA) under a nitrogen atmosphere employing four heating rates. The corresponding kinetic parameters of the two degradation stages were estimated by minimizing the output error functional and by the Kissinger method. In evaluating the kinetic parameters of the two‐step PU thermal decomposition, a differential thermogravimetry curve was applied as an objective functional in a regression procedure. Parameter estimation was obtained by minimizing the weighted quadratic output error functional with the modified Nelder–Mead simplex search algorithm. The confidence regions in the preexponential factor‐activation energy space were established for both the first and second stages of degradation. The effect of the molecular weight of the soft segment and the content of the hard segment on the activation energy of the degradation process was constructed by response surface methodology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 764–772, 2007     

Thermal degradation of cellulose in air and nitrogen at low temperatures

Thermal analysis and kinetic studies have shown that oxidative reactions are responsible for acceleration in the rates of weight loss and depolymerization of cellulose on pyrolysis in air at temperatures below 300°C. The oxidative reactions include production of hydroperoxide, carbonyl, and carboxyl groups, which have been investigated at lower temperatures along with the rates of depolymerization and production of carbon monoxide and carbon dioxide. The experimental results are consistent with an autoxidation mechanism involving initiation, propagation, and decomposition reactions. At temperatures above 300°, the rate of pyrolysis is essentially the same in both air and nitrogen, indicating that thermal degradation is independent of the oxidative reactions.     

Dynamic mechanical and morphological studies on the compatibility of plasticized PVC/thermoplastic polyurethane blends

In this work, the compatibility of blends of plasticized poly(vinyl chloride) (p‐PVC) and thermoplastic polyurethane (TPU) was investigated using a dynamic mechanical analyzer and scanning electron microscopy. Two kinds of TPU with different ratios of hard to soft segments, i.e., TPU90 and TPU70 were compared. p‐PVC/TPU90 and p‐PVC/TPU70 blends with variable weight ratios (100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 0/100) were prepared by melt blending. PVC was plasticized with 40 phr of dioctyl phthalate. It was found that TPU with a lower hard segment (i.e., TPU70) is more compatible with plasticized PVC than TPU with a higher hard segment (i.e., TPU90) in over the composition ranges examined. It was concluded that the compatibility of plasticized PVC and TPU are dependent on the ratio of hard to soft segments in TPU. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 415–422, 1999