聚合物PVT特性测试原理及设备

基于直接加压法原理(Piston-cylinder),研制了1种聚合物PVT(温度-比容积-温度)特性测试仪。该试仪测试压力范围为0.5~100 MPa,测试温度范围为30~300℃,最大冷却速率为45℃/s。通过对聚丙烯(PP)PVT特性测试表明:测试仪在较低的冷却速率下的重复精度为0.138%;对实验测试结果进行拟合,获得修正的双域Tait状态方程参数。同时,利用该装置研究了冷却速率对于聚合物PVT特性的影响。     

聚合物PVT关系在线测试技术

提出一种新的聚合物PVT(压力-体积-温度)关系在线测试技术,利用这种技术设计制造的聚合物PVT关系在线测试设备对低密度聚乙烯(LDPE)进行了PVT关系测试,测试条件符合工业加工条件。因此,利用此技术可以建立典型商业材料的PVT数据库,作为优化相应材料的工业加工参数的基础数据。     

聚合物PVT特性测试技术及状态方程进展

对聚合物压力?体积?温度（PVT）特性和测试技术重要性进行了阐述。介绍了PVT测试技术的发展现状，其中包括2种传统测试技术：直接加压法（圆筒柱塞法）和间接加压法（封闭液法）；基于传统测试方法改进的测试技术：高冷却速率柱塞法、改进型封闭液法和基于加工成型设备的在线测试技术。并且简述了聚合物PVT状态方程的发展现状。最后，总结了PVT特性和测试技术存在的问题和今后的研究方向。     

考虑冷却及剪切工况下的聚合物PVT特性研究历程及展望

综述了聚合物PVT特性及其在注射成型加工领域的应用。介绍了PVT测量仪从传统型到改进型的发展历程,其中传统测试技术包括直接加压法和间接加压法,而改进型则考虑了成型过程中冷却和剪切工况的影响。此外,总结了国内外关于冷却速率和剪切对聚合物PVT特性影响规律的研究历程,并对今后的研究方向进行了展望。     

一种新型聚合物熔体动态密度测量方法的研究

介绍一种聚合物熔体在不同温度及压力状态下熔体密度的测量方法,该方法基于聚合物熔体PVT相互关系原理,将测量微距离的读数百分表安装在改进结构的熔体流动速率试验机上,可以测量出任意熔融温度及压力下的聚合物熔体密度。通过对测量结果进行理论分析发现,聚合物熔体密度测量值符合聚合物自由体积理论,即聚合物熔体密度随温度升高而减小,随压力增大而增大。     

聚合物PVT特性在线测试技术及在模具设计中的应用

通过自主研发的聚合物压力比容温度（PVT）特性在线测试仪获得聚合物真实成型工况下的PVT特性参数,由此得到注射材料收缩率,用于制品模具成型尺寸设计,并计算得到以离线PVT参数为依据进行设计的模具成型尺寸。采用数值模拟方法对上述两种模具尺寸设计结果得到的成型制品精度进行对比分析。结果表明,以在线PVT测试结果为基础设计的模具成型尺寸得到的制品尺寸精度与实际设计要求更加接近。     

塑料精密注射模塑成型PVT特性测控方法研究

从聚合物材料压力比容温度(PVT)关系特性规律、塑料精密注射成型控制的核心原理、聚合物材料PVT特性测试仪、注塑缺陷在线诊断及自愈调控四个方面,对聚合物材料的PVT关系特性及其重要应用进行了介绍。     

聚合物PVT关系测试技术研究进展

对聚合物PVT关系测试的重要性及应用作了阐述,总结了聚合物PVT数据8个方面的应用;对当今世界上出现的聚合物PVT关系测试技术分别从常规和改进两个方面作了详细说明,常规测试方法归结为直接法和间接法,改进测试技术包括考虑冷却速度、形变对聚合物PVT关系影响的测试技术、基于注塑机挤出机的测试技术、超声波测试技术;并对几种聚合物PVT关系测试产品作了介绍,包括德国SWQ公司的PVT-100分析仪、日本东洋精机公司的PVT测试仪、美国Gnomix公司的高压膨胀计,以及国内聚合物PVT在线测试设备。     

可降解聚乙醇酸结晶行为与性能的构效关系

聚乙醇酸（PGA）是半结晶聚酯材料，兼具生物降解性与生物相容性，在手术缝合线、组织支架等生物医用领域发挥重要作用。文章从PGA的化学结构、晶体结构、等温结晶动力学研究、非等温结晶动力学等方面详细论述PGA材料的高分子结晶热力学与动力学模型。研究表明：在加工工艺中对加工温度、压力和冷却速率等参数进行控制，可确保最终产品具有所需的性能。通过添加适当的添加剂或改变材料的分子结构可调节高分子材料的结晶度，以满足PGA在具体应用的使用要求，也为改善与拓展生物相容性PGA高分子材料的应用提供技术方案。     

超声检测在聚合物PVT关系测试中的应用

聚合物加工过程发生物态转变,测试对应的PVT数值变化对于精确控制工艺参数极其重要.概述PVT的检测方法,并研究超声波信号与聚丙烯PVT特性的相互关系.实验显示:在熔融状态超声波声速与聚丙烯比容(密度)存在线性对应关系.可通过超声波来间接测试聚合物熔体密度的变化,为精密加工提供控制的基础.     

The use of master curves to describe the simultaneous effect of cooling rate and pressure on polymer crystallization

In a previous work a master‐curve approach was applied to experimental density data to explain isotactic polypropylene (iPP) behaviour under pressure and high cooling rates. Suitable samples were prepared by solidification from the melt under various cooling rate and pressure conditions with the help of a special apparatus based on a modified injection moulding machine. The approach here reported is more general than the case study previously shown, and is suitable to be applied to several materials and for different measures related to crystalline content. The proposed simple model is able to predict successfully the final polymer properties (density, micro‐hardness, crystallinity) by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions. For this purpose three semi‐crystalline polymers were studied [iPP, polyamide‐6 (PA6) and poly(ethyleneterephthalate) (PET)], which exhibited remarkably different behaviour when crystallized under pressure and high cooling rates Copyright © 2003 Society of Chemical Industry     

Burning Rate Characterization of GAP/HMX Energetic Composite Materials

The burning rate of the energetic materials composed of glycidyl azide polymer (GAP) and HMX particles was characterized in order to elucidate the heat release process during burning. Since GAP is an energetic polymer and burns by itself, the addition of HMX increases the flame temperature and alters the burning rate characteristics. Experimental observations indicate that the gas phase structure consists of a two‐staged gas phase reaction: the burning rate is controlled by the first‐stage reaction zone and the final flame is formed at the second‐stage reaction zone. The heat flux transferred back from the first‐stage reaction zone to the burning surface increases as pressure increases and the heat released at the burning surface remains unchanged when pressure is increased.     

Bi-directional freeze casting of porous alumina ceramics: A study of the effects of different processing parameters on microstructure

Highly aligned lamellar ceramic scaffolds were produced using a bi-directional freeze casting technique. A specially designed, sloped copper mould was covered with a polymer to modulate the temperature field. Effects of different processing parameters (cooling rate, mould slope angle, ceramic solid loading and binder concentration) on lamellar orientation were systematically studied. The results showed that freezing under a dual temperature gradient produced highly aligned ceramic scaffolds. Increasing both the cooling rate and the mould slope angle increased the size of the ordered ceramic region. Using different alumina solid loadings in the initial suspension had little effect on the aligned lamellar structure. Increasing the binder concentration affected ice crystal growth in a highly aligned direction. Therefore, freeze casting using a dual temperature gradient can be used to fabricate highly aligned porous materials.     

Effects of glass‐fiber content and coolant temperature on temperature and crystallinity profiles of PP melt during cooling

This investigation studied the temperature gradients and degree of crystallinity of polypropylene melt across a circular duct during the cooling process, where the coolant used was chilled water. The effects of glass‐fiber content, varying from 0 to 44 wt %, and coolant temperature, varying from 5 to 20°C, were our main interest. The results suggested that the rate of cooling of the polymer of each position across the duct was not significantly affected by the temperature of the coolant and glass‐fiber contents, although the rate of cooling was influenced by the size of the duct. The crystallization temperature and degree of crystallinity of the polymer increased with increasing glass fiber contents and the coolant temperature. These phenomena were associated with the heat transfer between the coolant and the polymer, crystallization temperature, exothermic crystallization process, and thermal properties of the polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2087–2097, 2001     

The effect of injection molding process parameters on mechanical and fracture behavior of polycarbonate polymer

In this work, the mechanical and failure behavior of injection molded aviation standard optical grade polycarbonate (PC) was investigated through uniaxial tensile testing. The effect of different injection molding process parameters including injection velocity, packing pressure, cooling time, mold temperature, and melt temperature were determined to observe their effect on yield and postyield behavior of PC. Out of these examined parameters, the mold and melt temperature show significant effect on mechanical behavior of studied polymer. The yield and flow stresses in polymer increase with the increase in mold and melt temperature during injection molding. However, other process parameters i.e., packing pressure, injection velocity, and cooling time showed little effect on mechanical performance of the polymer. The molded specimens were annealed at different temperatures and residence time to evaluate its effect on mechanical behavior and fracture morphology. The yield stress increases gradually with the increase in annealing temperature and time. The annealing treatment also changed the failure mode of PC specimens from ductile to brittle. In addition to process parameters, the effect of increased loading rate was also undertaken which shows substantial effect on mechanical and failure behavior of PC. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44474.     

PTFE／GF透波复合材料成型工艺与性能研究

为制备高性能聚四氟乙烯(PTFE)基透波复合材料,对玻璃布(GF)增强PTFE的成型工艺进行了研究。通过差示扫描量热法确定了PTFE/GF复合材料的烧结温度,考察了烧结时间、冷却速率、压制压力及组分配比等因素对复合材料性能的影响。结果表明,当GF质量含量为40%、压制压力为45MPa时,PTFE/GF复合材料的拉伸强度最大,可达81.2MPa,介电性能也满足透波复合材料的要求。     

异形纤维纺丝技术探讨

论述了异形纤维的纺丝技术 ,着重探讨了喷丝孔形状 ,聚合物摩尔质量、纺丝温度、熔体压力 ,喷丝板拉伸倍数 ,冷却条件与纤维异形度之间的关系。指出了不同孔形纺制的异形纤维 ,异形度相差很大 ;随着摩尔质量增加 ,异形度变大 ;温度和压力提高 ,异形度下降 ;纺丝速度影响不大 ;泵供量加大 ,冷却条件加剧 ,可使异形度上升     

Pressure and cooling rate‐induced densification of atactic polystyrene

The exact knowledge of postprocessing polymer‐specific volume is often a factor of enormous strategic importance from an industrial point of view. The subject is complicated by the fact that the specific volume of solid polymers at a constant temperature and pressure is not only a function of the current temperature and pressure, but is also a consequence of the whole formation history from the melt. In this work, specific volumes of samples solidified in different conditions are analyzed and related to their formation history. A wide range of cooling rates (from 5 × 10^?3 to 300 K/s) and solidification pressures (from 0.1 to 80 MPa) are examined. The results show a synergic effect of the cooling rate and solidification pressure: Lower cooling rates result in a much higher pressure‐induced densification with respect to higher cooling rates. A simple phenomenological model which essentially links the densification effect to the dependence of the glass transition temperature upon the cooling rate and solidification pressure is adopted to describe the experimental data. Starting from the densification effect, the effect of the pressure and cooling rate on the glass transition temperature is evaluated. Furthermore, some conclusions about the dependence of the volume relaxation time on the temperature and pressure in the glass transition range are achieved. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 184–190, 2003     

Development of stress birefringence and flow patterns during mold fillin and cooling

An experimental study was carried out to investigate the development of stress birefringence patterns of molten polymer during the mold filling and cooling operation. For this study, a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a movie film the changes in stress birefringence patterns in the mold cavity during the molding operation, using a circular polariscope. The mold was equipped with an automatic relay system which closes the shut-off valve when the pressure in the mold cavity reaches a predetermined value. The mold was also equipped with both heating and cooling devices, so that either isothermal or non-isothermal injection molding could be carried out. The mold temperature was controlled by thermistor regulated controllers. During the entire cycle of the molding operation, the mold cavity pressure was continuously recorded on a chart recorder, using a melt pressure transducer. The present study shows how molding conditions (namely, injection pressure, melt temperature, mold temperature) influence the distribution of stress birefringence patterns in a molten polymer while it is being injected into, and cooled in, a rectangular mold cavity.     

Modifying the tait equation with cooling-rate effects to predict the pressure–volume–temperature behaviors of amorphous polymers: Modeling and experiments

Cooling-rate effects play an important role in polymer processing because the materials experience rapid cooling when transferring from melt states to solid states. The traditional Tait equation has been used widely in representing the volumetric behaviors of polymers as a function of temperature and pressure, but not of cooling rate. Based on the dependence of glass-transition temperature on cooling rate (i.e., θ = dT_g/d log ∣ q ∣), the volumetric dependence on cooling rate is employed in this work to modify the traditional Tait P–V–T equation to become a time-dependent P–V–T model. The physical meanings of the traditional Tait equation parameters are interpreted and, thereby, parameters in the new model are derived according to the material constant θ. The controlled cooling-rate measurements of polymeric volumetric data have been performed in this work to verify the validity of the proposed model. Additionally, the material parameter θ, calculated from the measured data of polystyrene (PS) (Chi-Mei PG-33) in this work, equals 2.85 K, which is close to 2.86 K calculated from the Greiner-Schwarzl work. Furthermore, a comparison of the predicted results with the experimental data both in this work and from literature is discussed under different pressures and various cooling rates. The results have indicated that the proposed non-equilibrium P–V–T model closely correlates with experimental data.