苯乙烯-丁二烯-苯乙烯嵌段共聚物/聚(苯乙烯- 甲基丙烯酸甲酯)热塑性互穿聚合物网络

采用原子转移自由基聚合(ATRP)和分步方法,制备了以苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)为聚合物Ⅰ,聚(苯乙烯-甲基丙烯酸甲酯)[P(St—MMA)]为聚合物Ⅱ的SBS／P(St—MMA)热塑性互穿聚合物网络(TIPN)。研究了P(St—MMA)质量分数、MMA／St(摩尔比)和不同聚合方式对TIPN动态力学性能和黏结性能的影响。结果表明,采用ATRP法制备的TIPN的动态力学性能和黏结性能均优于常规自由基聚合制备的TIPN。高温区聚苯乙烯(PSt)嵌段的玻璃化转变温度明显降低,而损耗角正切tanδ2显著增加;TIPN的黏结性能也得到明显改善,拉伸剪切强度提高了3倍多。     

SBS/P(St-MMA)热塑性互穿聚合物网络结构与力学性能

采用原子转移自由基聚合(ATRP)法合成了苯乙烯一甲基丙烯酸甲酯共聚物[P(St-MMA)]。采用分步法制备了SBS／P(St-MMA)热塑性互穿聚合物网络(TIPN)。研究了P(St-MMA)质量分数、MMA／St(摩尔比,下同)和不同聚合方式对TIPN结构和力学性能的影响。结果表明：生成了具有较窄相对分子质量分布的P(St-MMA);P(St-MMA)质量分数在30％,左右时,采用ATRP法制备的SBS／P(St-MMA)TIPN拉伸强度和扯断伸长率达到最大;随MMA／St增加,TIPN拉伸强度增大,扯断伸长率不变。常规自由基聚合法制备的TIPN与ATRP法相比,前者相对分子质量高,相对分子质量分布宽,拉伸强度高,扯断伸长率随P(St-MMA)质量分数增加而下降。     

苯乙烯和甲基丙烯酸甲酯梯度共聚物的应用

将用原子转移自由基聚合及连续补加甲基丙烯酸甲酯（MMA）的方法制备的苯乙烯（St）/MMA梯度聚合物P（Pt-t-MMA）作为增容剂应用于聚氯乙烯/苯乙烯-丁二烯-苯乙烯嵌段共聚物（PVC/SBS）和PS/PMMA聚合物合金的增容和改性。扫描电镜结果表明,P（St-t-MMA）可以改善PVC/SBS和PMMA/PS合金的相容性。PVC/SBS合金中加入少量P（St-t-MMA)后,冲击强度从6.0kJ/m^2提高到12.1kJ/m^2,加工流变性能得到了改善。SBS用量也影响PVC/SBS合金的冲击强度。     

EPDM-g-MS/MS共混物的热性能及流变性能

用溶液聚合法合成的EPDM（乙烯／丙烯／二烯共聚物）与MMA（甲基丙烯酸甲酯）及St（苯乙烯）接枝共聚物（EP—DM—g—MS）与MS（苯乙烯-甲基丙烯酸甲酯共聚物）树脂共混制备MES（EPDM—g—MS增韧MS），通过热重分析研究了MES的热稳定性，通过测试MES的表观粘度、非牛顿指数和粘流活化能等流变参数，分析其流变性能。结果表明，MES具有较好的耐热性能，且随EPDM-g—MS含量及MMA／St配比的增加而提高。MES的非牛顿指数小于1，符合假塑性流体流动规律。其表观粘度随剪切速率和温度升高而降低，随EPDM-g—MS含量增加而提高。MES的粘流活化能小于MS树脂的。     

SBS/PS共混物耐疲劳性能研究

研究了熔融法制备苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)/聚苯乙烯(PS)共混物的耐疲劳性能.结果表明,随着PS含量的增加,SBS/PS共混物屈服强度增大,由韧性断裂变成脆性断裂.而断裂强度和断裂伸长率随着PS含量的增加而降低.在动态载荷作用下,SBS/PS共混物动态疲劳的最大负载和平衡负载随着PS含量的增加而增大....     

PPS/PA1010合金的制备及其力学性能研究

选用丙烯酸接枝聚丙烯（PP-g-AA）和自制的甲基丙烯酸缩水甘油酯（GMA）嵌段共聚苯乙烯（St）接枝聚丙烯[PP—g-（GMA—CO—St）]为增容剂,采用双螺杆挤出机熔融挤出法制备了PPS／PA1010／PP—g—AA合金和PPS／PA1010／PP-g-（GMA—CO-St）合金,并分别对两种合金的力学性能进行了研究。结果表明,在保持合金其它力学性能不下降的情况下,随着PP—g—AA含量的增加,共混合金的冲击强度先提高后降低,当PP-g—AA含量为7份时,冲击强度比原合金提高了86．7％,比纯PPS提高了39．3％;而随着PP—g-（GMA—CO—St）含量的增加,冲击强度也有明显提高。     

PP/PVC/PP-g-(St-co-MMA)的形态结构

以苯乙烯一甲基丙烯酸甲酯共聚物接枝聚丙烯[PP—g-（St—co—MMA）]为相容剂，利用扫描电子显微镜（SEM）和x射线能谱仪（EDS）对PP／PVC／PP—g-（St—co-MMA）的形态结构进行了研究。由x射线能谱微区分析得到了共混物中氯元素面分布图，对氯元素面分布进行了粒径统计。结果表明，在PP／PVC中加入PP-g-（St—co—MMA）相容剂，共混物亚微观相形态结构发生了变化。PP—g-（St—co—MMA）能够明显降低PP／PVC共混物中PVC分散相的分散尺寸，提高共混物两相之间的相容性。改变相容剂的用量和共混物的组成，都对体系的形态结构产生影响。     

SBS/PS共混物力学性能及老化行为研究

通过熔融共混法制备苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)/聚苯乙烯(PS)共混物,研究共混物的力学性能、熔体流动速率、耐热性能及耐老化性能。结果表明,随着PS质量分数由0增加到40%,SBS/PS共混物拉伸屈服强度由4.71 MPa增至12.11 MPa;SBS/PS的冲击强度呈现下降趋势;SBS/PS共混物的熔体流动速率由0.60g/10min下降至0.14g/10min,SBS/PS共混物的维卡软化点由53.8℃升到72.1℃。热氧、光氧、人工气候老化试验发现,随着PS用量的增加,SBS/PS共混物的耐热氧、耐光氧及耐老化能力增强。     

接枝改性SBS对PS/SBS/CaCO_3复合材料形态和力学性能的影响

采用马来酸酐(MAH)和苯乙烯(St)作为接枝单体,通过溶液聚合法合成接枝极性基团的苯乙烯-丁二烯-苯乙烯三嵌段共聚物(SBS),然后与聚苯乙烯(PS)基体、碳酸钙(CaCO_3)粒子复合,用傅立叶红外光谱仪表征接枝处理前后SBS表面化学结构的变化;并研究了SBS改性对复合材料微观结构和力学性能的影响.结果表明:双单体溶液聚合法成功地将极性基团接枝在SBS链上;填充SBS-g-MAH后,促进CaCO_3在PS基体中的分散、改善PS-CaCO_3粒子间界面粘接,起到良好的增容作用;SBS-g-MAH和CaCO_3粒子对PS基体具有协同增强增韧作用,同时能提高复合材料的拉伸强度和冲击强度.     

EPDM-g-MS对MS树脂的增韧作用

用溶液聚合法合成三元乙丙橡胶（EPDM）与甲基丙烯酸甲酯（MMA）及苯乙烯（St）接枝共聚物（EPDM-g-Ms），用其与MMA／St共聚物（Ms树脂）共混制备高抗冲塑料（MES），研究了EPDM-g-MS对MS树脂的增韧作用，用扫描电子显微镜（SEM）和透射电子显微镜（TEM）对MES的微观相结构进行了分析。结果表明：EPDM-g-MS的接枝率、接枝链的极性及EPDM在MES中的含量是影响其对MS树脂增韧效果的主要因素。增加EPDM-g-MS的接枝率、增强其接枝链的极性及增加其用量均可提高MES的缺口冲击强度。MES相结构的TEM分析和冲击断面形态的SEM分析表明，随着EPDM在MES中的含量的增加，EPDM-g-MS分散相的粒径增大，粒面距离缩短，导致IVIES的增韧机理由空穴化向轻度剪切屈服转变，IVIES的缺口冲击强度随之而提高。     

Effect of the fabrication process on the microstructural evolution of carbon fibers and flexural property on C/SiC composites by the NITE method

Nano-infiltration and transient eutectic phase (NITE) SiC matrix composites are designed for application in aerospace propulsion systems, particularly in fasteners and thrusters. A variety of carbon fibers with different properties have been selected as reinforcements for SiC matrix composites. Carbon fibers are known to be stable at high temperatures; however, the effects of high applied pressure at high temperatures on the fiber microstructure evolution and mechanical properties are not well-known. As a scoping study for fabricating NITE C/SiC composites, the behaviors of various carbon fibers in SiC composites. Pitch-based fibers, namely, GRANOX XN-05 and YS-90A, and a polyacrylonitrile-based fiber, namely, TORAYCA T-300B, were selected for matrix reinforcement. The 3-point bending test results indicated pseudo-ductile behaviors in the cases of YS-90A and T-300B fiber reinforcements. Fracture resistance evaluation based on the single-notch bending test indicated that the YS-90A fiber reinforced composite afforded the highest fracture resistance among the three C/SiC composites. The microstructure evolution on YS-90A and T-300B fibers was limited to near the fiber surface. Therefore, YS-90A and T-300B carbon fibers are potential candidates for reinforcement in NITE C/SiC composites.     

A method based on isothermal calorimetry to quantify the influence of moisture on the hydration rate of young cement pastes

Cement hydration needs water to proceed and if water is lost by drying, the hydration rate will decrease. This can be of importance in cases when concrete surfaces are exposed to drying so that their strength development will be retarded. We describe a method based on isothermal calorimetry to assess how the rate of cement hydration is influenced by removal of water (drying) at different times up to three days after mixing. Thin samples of cement pastes are hydrated in a calorimeter and at different times exposed to one hour drying periods. The resulting decrease in thermal power following the removal of water is quantified as a measure of the reduction in hydration rate. The mass loss is found by weighing the samples before and after a measurement, and the change in water activity of a sample during drying can be found from the slope of the thermal power during the drying period.     

Effect of carbonation on the hydro-mechanical properties of Portland cements

We evaluate experimentally the effect of carbonation on the hydro-mechanical properties of Portland cement. Samples were carbonated at 90 °C and 28 MPa under wet supercritical CO₂. Two types of carbonation features were achieved, either the samples were homogeneously carbonated or they displayed sharp carbonation fronts. Using a tri-axial apparatus, the static elastic moduli and the mechanical strength were measured at in-situ pressure conditions (28 MPa) and showed a degradation of the mechanical properties of the samples where a carbonation front prevailed. Water and gas permeabilities were measured and showed that the samples with a carbonation front exhibit a stress sensitive permeability. P and S elastic wave velocities were measured to evaluate dynamic (ultrasonic range, 1 MHz) elastic moduli. The use of an effective medium theory approach enabled us to characterize the density and distribution of cracks within the samples. This approach outlines that the samples which developed a carbonation front were damaged.     

Influence of the nature of aggregates on the behaviour of concrete subjected to elevated temperature

An experimental study is carried out on concretes composed of three different types of aggregates: semi crushed silico-calcareous, crushed calcareous and rolled siliceous. For each aggregate type, two water/cement ratios (W/C), 0.6 and 0.3 are studied. Aggregates and concrete specimens were subjected to 300, 600 and 750 °C heating–cooling cycles. We analyse the evolution of thermal, physical and mechanical properties of concrete in terms of behaviour and physical characteristic evolutions of aggregates with temperature. The study of thermal behaviour of aggregates showed the importance of initial moisture state for the flints. The crystallisation and microstructure of quartz play an important role in the thermal stability of siliceous aggregates. The residual mechanical behaviour of concrete varies depending on the aggregate and the influence of aggregates is also dependent on paste composition. This study allowed to better understand the influence of chemical and mineralogical characteristics of aggregates on the thermomechanical behaviour of concrete.     

交联剂的用量对淀粉-壳聚糖-聚乙烯醇-明胶共混膜的性能影响

本文研究了交联剂对淀粉/壳聚糖/聚乙烯醇/明胶共混膜的透光性、透气性、吸水性及保水性和力学性能的影响。结果表明：共混膜的性能与交联剂有较大关系。在交联剂用量在0%~5%的范围内,随着交联剂用量的增加,共混膜的扯断伸长率、吸水性和保水性随之降低,共混膜的拉伸强度、撕裂强度、透水气性和透光性先增加后减小。     

Impact of admixtures on the hydration kinetics of Portland cement

Most concrete produced today includes either chemical additions to the cement, chemical admixtures in the concrete, or both. These chemicals alter a number of properties of cementitious systems, including hydration behavior, and it has been long understood by practitioners that these systems can differ widely in response to such chemicals.In this paper the impact on hydration of several classes of chemicals is reviewed with an emphasis on the current understanding of interactions with cement chemistry. These include setting retarders, accelerators, and water reducing dispersants. The ability of the chemicals to alter the aluminate–sulfate balance of cementitious systems is discussed with a focus on the impact on silicate hydration. As a key example of this complex interaction, unusual behavior sometimes observed in systems containing high calcium fly ash is highlighted.     

The influence of water removal techniques on the composition and microstructure of hardened cement pastes

The removal of water from hardened cement paste for analysis or to arrest ongoing hydration has been reported to affect the composition of hydrated phases and microstructure. The effect that arresting the hydration of hardened cement paste by replacing the pore water with acetone before drying, and by removing the water by freeze, vacuum and oven drying has on the hardened cement paste has been investigated. Two pastes were studied, a cemented iron hydroxide floc where a high proportion of ordinary Portland cement (OPC) had been replaced by pulverised fuel ash, and a pure hydrated OPC. The results showed that none of the water removal techniques caused any major deterioration in the composition and microstructure of the hardened cement pastes studied, but the pores appeared better preserved after arresting hydration using acetone quenching. Freeze drying appeared to cause more cracking of the microstructure than the other water removal techniques.     

Effect of the variations of clinker composition on the poroelastic properties of hardened class G cement paste

The effect of the variations of clinker composition on the poroelastic properties of class G oil-well cement pastes is studied using a multiscale homogenization model. The model has been calibrated in a previous work based on the results of a laboratory study. Various compositions of class G cements from literature are used in a hydration model to evaluate the volume fractions of the microstructure constituents of hardened cement paste. The poroelastic parameters such as drained bulk modulus, Biot coefficient, and Skempton coefficient are evaluated using the homogenization model. The results show that the variations in chemical composition of class G cements have no important effect on the variations of the poroelastic properties.     

Influence of gypsum additive on the gyrolite formation process

The influence of gypsum additive on the gyrolite formation process and a sequence of intermediary compounds formation in the CaO-SiO₂·nH₂O-H₂O system was examined and explained. The synthesis has been carried out in unstirred suspensions. The molar ratios of primary mixtures were CaO/SiO₂ = 0.66. The amount of sulphate ions to be added to a raw mixture was 1-10%. The duration of isothermal curing at 200 °C was 4, 8, 16 and 72 h.It was determined that the quantity of sulphur which penetrates into the crystalline structure of gyrolite depends not only on the synthesis conditions but also on the composition of initial mixture. A larger amount of sulphate ions stimulate the formation not only of gyrolite, but also of CaSO₄. Gypsum additive has no influence on the re-crystallization temperature of C-S-H(I), Z-phase and gyrolite into wollastonite. The composition of initial mixtures is recommended to calculate according to molar ratios. In other cases, upon increasing the amount of sulphate ions, the basicity of the mixture decreases and gyrolite forms more difficult.     

Effect of fly ash on the kinetics of Portland cement hydration at different curing temperatures

This paper describes the effect of fly ash on the hydration kinetics of cement in low water to binder (w/b) fly ash-cement at different curing temperatures. The modified shrinking-core model was used to quantify the kinetic coefficients of the various hydration processes. The results show that the effect of fly ash on the hydration kinetics of cement depends on fly ash replacement ratios and curing temperatures. It was found that, at 20 °C and 35 °C, the fly ash retards the hydration of cement in the early period and accelerates the hydration of cement in the later period. Higher the fly ash replacement ratios lead to stronger effects. However, at 50 °C, the fly ash retards the hydration of the cement at later ages when it is used at high replacement ratios. This is because the pozzolanic reaction of the large volumes of fly ash is strongly accelerated from early in the aging, impeding the hydration of the cement.