Isothermal crystallization of iPP in model glass-fiber composites

Isothermal crystallization of iPP in model glass-fiber composites is studied by DSC, and the basic energetic parameters of crystallization are determined. Unsized untreated and thermally treated glass fibers are used in model composites to determine the role of the surface on nucleation and crystallization processes. Thermally treated glass fibers are found to exhibit a predominant nucleating effect as compared to unsized untreated ones, and the crystallization proceeds faster, resulting in lower values for the half-time of crystallization (10–120 s). The energy of formation of a nuclei of critical dimensions at a given T_c is also lower, and it decreases as the content of the fibers in the composite increases. The surface free energy of folding, σ_e = 140 × 10⁻³ J/m², was determined for iPP in the composite containing 50% glass fibers, while for pure iPP, σ_e = 170 × 10⁻³J/m² was found. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 381–389, 1998     

硫氮玻璃的析晶性能与结构分析

通过对二元（Ｇｅ－Ｓ）和三元（Ａｓ－Ｇｅ－Ｓｅ）系统硫系基玻璃和引入Ｓｉ３Ｎ４的硫氮玻璃试样析晶性能的比较,对硫氮玻璃的析晶行为与其结构之间的关系进行了较深入的探讨。试验结果表明,随着Ｓｉ３Ｎ４的引入,硫系玻璃的析晶温度得以提高或伴随析晶放热峰的消失。这表明氮原子的引入加强了硫系基玻璃微观结构的连缀度,使硫氮玻璃的析昌能力有所下降。此外还在经过析晶热处理的硫氮玻璃试样的ＸＲＤ中发现两个新衍射峰,且     

DSC analysis of crystallization and melting behavior of polypropylene in model composites with glass and poly(ethylene terephthalate) fibers

Isothermal and nonisothermal crystallization of maleic anhydride grafted polypropylene (PP), which is used for the production of split warp knit composite preforms,¹ are analyzed in model composites to determine the influence of reinforcement glass fibers (GF) and poly(ethylene terephthalate) (PET) binding yarns on the crystallization kinetics. Basic energetic parameters of crystallization are determined, and the melting behavior of PP in model composites is analyzed. The crystallization of PP carried out in nonisothermal and isothermal regimes is facilitated in the presence of GF, and the additional effects of PET fibers are also shown. Better conditions for nucleation, resulting in lower energy for formation of a stable nucleus and lower critical dimensions, are proposed as a reason for this. The crystal structure of PP in model composites exhibits lower lamellae thickness and is less disposed to recrystallization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 239–246, 1999     

The crystallization and rheological behaviors of in situ microfibrillar isotactic polypropylene/polyamide 66 composites with a selective β-nucleating agent distribution

In situ microfibrillar composites (MFCs) with isotactic polypropylene (iPP) as matrix and β-nucleating agents filled polyamide 66 (β-PA66) as dispersed microfibrils were fabricated through multistage stretching extrusion technology. The simultaneous effects of β-nucleating agents, shear-flow and microfibrils on the crystallization and rheological behaviors of iPP were explored. Crystallization analysis demonstrated that the counteraction of shear flow and β-nucleating agents resulted in the absence of β-crystal in the as-extruded MFCs. When the MFCs were annealed at 210°C for 10 min, the flow field was erased accompanied with the migration of β-nucleating agents from PA66 phase to surface, which in turn inducing the formation of β crystal in the recrystallized samples. Shear rheological investigations suggested that the β-NAs at interface mechanically integrated the PA66 and iPP phase thus improving the interfacial adhesion. These findings provided a potential way to solve the interfacial problems of MFCs.     

Modeling the Ultimate Tensile Strength of Unidirectional Glass-Matrix Composites

The ultimate tensile strengths of a unidirectional glass-matrix composite were measured as a function of fiber volume fraction. The results were compared with predictions, using a refined solution of the stress field generated by an axisymmetric damage model, which incorporated the effect of stress concentration in the fiber caused by the presence of a matrix crack both before and after deflection at the fiber/matrix interface. Two possible locations for the fiber failure were considered: (1) at a transverse matrix crack, near a bonded fiber/coating interface and (2) at the tip of a debond, at the fiber/coating interface. At low fiber volume fractions, the measured ultimate tensile strength matched the prediction calculated, assuming no crack deflection. For higher volume fractions, the predictions calculated for a debonded crack matched the observed values. The model results were relatively insensitive to debond length and interfacial shear stress for the range of values in this study. In comparison, the global load-sharing model, which does not account for the stress singularity at the fiber/matrix interface, was found to overpredict the values of the ultimate tensile strength for all fiber volume fractions. An important contribution of the present work was to introduce the use of fiber volume fraction as a parameter for testing theoretical predictions of the mode of fiber failure.     

Processing Effects on the Surface Composition of Glass Fiber

In this study, differences in the surface composition of commercial glass fiber have been characterized as a function of process. The two processes studied were flame attenuation, a high-temperature combustion-assisted process, and continuous filament drawing through a bushing. The techniques used to determine the surface compositions were TOF-SIMS and XPS; the presence of a very thin, boron-depleted silica-enriched layer on the flame-attenuated fibers was most significant. Thermodynamic modeling of the equilibrium vapor pressures at the surface, during fiberization, showed significant differences in the behavior of Na, B, and F species in the two processes. To further test the models, glass fibers were produced under more closely controlled conditions in a laboratory-scale flame attenuation system. These experiments verified the important effect of flame temperature and residence time in creating the surface layer.     

Characterization of biodegradable core–clad borosilicate glass fibers with round and rectangular cross-section

Here, we report on core–clad bioactive borosilicate fibers, that we have prepared both with round and rectangular cross-section profile. The exposed approach, which relies on the stacking and drawing of glass slabs, demonstrates our ability to develop bioactive-based glass fibers with tailored cross-section profiles. Tens-of-meters-long fibers were successfully drawn, although suffering from elevated losses in the case of the rectangular ones. The response of the fibers in simulated body fluid was studied for both geometries. We found that a round cladding can act as protective layer, tempering effects of the corrosion. We also noticed that rectangular fibers are more prone to degradation, the enhanced corrosion beginning from their sharp corners as they accumulated residual tensile stress during drawing. To the best of our knowledge, this is the first report on the effect of residual tensile stresses from surface tension deformations applied to the corrosion of rectangular fibers. As geometry plays a critical role on the biodegradation behavior of the fiberglass, we believe the enclosed results could lead to the design of fiber devices with tailored cross-section profile in order to tune their rate of degradation on solely based geometrical effects.     

CaO-Al2O3-SiO2系统微晶玻璃表面析晶动力学研究

采用X衍射分析（XRD）,扫描电镜分析（SEM）等测试分析手段,研究了CaO-Al2O3-SiO2（以下简称CAS）系统微晶玻璃的析晶动力学。通过块状样品的析晶趋势表征了表面析晶模式,计算了晶体生长阶段的析晶速率;采用SEM测试方法分析了玻璃颗粒中晶体长大过程。     

掺入硫硒化镉硼硅酸盐玻璃的析晶行为

在硼硅酸盐玻璃中引入少量硫(硒)化镉能获得从黄色至红色的系列颜色玻璃。这方面的工作是从三十年代开始的。到了六十年代这种玻璃以其优异的光谱特性(如光截止吸收性能)而在红外光学领域引起人们的重视。人们对这种玻璃的配方、熔制工艺及着色机理等进行了广泛的研究。近年来,许多研究者发现这种含大小为100至1000的半导体     

砷碲玻璃的析晶研究及其结构探讨

借助于各种热处理技术、DSC和XRD方法,研究了砷碲系玻璃的析晶过程。实验结果表明:砷蹄系统的玻璃转业点T_e和初始析晶温度T_(er)随砷浓度增加而升高,而析晶速率则减慢;在较低温度(T≥T_3)或析晶初期,得到的晶相基本上均为具有NaCl型结构的亚稳态晶体AsTe,而在高温或析品末期,得列的均为相图平衡相晶体。本文在实验基础上,提出一个新的砷碲玻璃的结构模型。认为砷碲玻璃的结构网络是由砷碲原子比相等的结构基团或局域单元联缀而成。它们基本上是类似于As_4S_4的As_4Te4结构或其它的复合形式。余下的砷或碲分布在其间并把它们相互连接起来。     

空心与实心玻璃纤维及其复合材料性能研究

对比研究了空心玻璃纤维与实心玻璃纤维单丝及复丝拉伸强度,建立了玻璃纤维单丝强度模型。通过缠绕工艺及模压工艺制备了空心/实心玻璃纤维复合材料(HGFRP/SGFRP)单向板,考察了HGFRP及SGFRP单向板的拉伸性能及弯曲性能。研究表明,空心玻璃纤维及实心玻璃纤维单丝拉伸强度均符合Weibull分布,空心玻璃纤维单丝及复丝的拉伸强度低于实心玻璃纤维,HGFRP的比拉伸强度和比弯曲强度略低于SGFRP,但HGFRP的比拉伸模量和比弯曲模量高于SGFRP。研究表明,空心玻璃纤维有望在新一代轻质高强材料中发挥新型异型纤维增强体的作用。