Polyimide incorporated cyanate ester/epoxy copolymers for high-temperature molding compounds

The rapid development of high-power devices has driven the requirement for high-temperature stable epoxy molding compounds. In this work, a designed polymer blend system consisting of cyanate ester/epoxy copolymers modified by polyimide (CE/EP-PI) has been studied. Polyimide used in this study has shown excellent dispersity in the cyanate ester and epoxy copolymer network (CE/EP), exhibiting homogeneous phase with a denser polymer network structure. With this polymer blend structure, CE/EP-PI system was proved to have a glass transition temperature as high as ~270 °C, increased modulus, and largely enhanced fracture toughness up to 2.06 MPa m^1/2. CE/EP-PI resins showed outstanding long-term stability at high temperature with low mass loss and increased fracture toughness after aging at 200 °C. This work provides a novel insight into the development of molding compounds based on polymer blends system with excellent high-temperature properties. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2412–2421     

Analytical review of some relevant methods and devices for the determination of the specific volume on thermoplastic polymers under processing conditions

This article reviews some of the most representative methods and devices to measure the specific volume in polymeric materials found in literature. Each method is described and a comparison between the experimental conditions and typical injection molding processing conditions is discussed. In general, the main difficulty with specific volume measurements is determination of the temperature distribution through sample thickness, particularly when achieving typical processing conditions is intended. Therefore, the necessity of developing a new device which allows direct measurements of pressure and temperature at various positions along the sample thickness in order to calculate the cooling condition was identified.     

Soft lithography microfabrication of functionalized thermoplastics by solvent casting

A soft lithographic method is described for casting functional thermoplastic devices with microscale features without the need for specialized tools or equipment. In the thermoplastic soft lithography process, termed solvent casting, low temperature supersaturated solutions of thermoplastic are poured over solvent permeable PDMS molds which allow omnidirectional solvent removal as they template functional microstructures into the thermoplastic layers. Rapid gelation of supersaturated solutions enables the deposition of multiple patterned layers of varying composition, with self‐adhesion of the solvent‐laden thermoplastic ensuring intimate bonding between adjacent layers. This latter feature is further used in this work to realize sealed thermoplastic microfluidic devices with high fidelity replication of microchannel features with negligible channel deformation. The incorporation of functional dopants into patterned thermoplastic layers allows the fabrication of thermoplastic devices with embedded fluorescent sensors and integrated conductive elements. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1315–1323     

Influence of pineapple leaf fiber and it's surface treatment on molecular orientation in,and mechanical properties of,injection molded nylon composites

The objective of his work is to show that pineapple leaf fiber (PALF) can be used successfully to reinforce a high melting polymer such as nylon. One of the most important barriers to the utilization of lignocellulosic materials in polymer matrix composites is their limited temperature resistance. As a consequence, they are mostly used to reinforce low melting temperature polymers such as polyethylene and polypropylene as well as polystyrene. However, this work reveals that PALF can be used to reinforce nylon. This is because of its very low lignin content. Nylon 6/66 composites containing a fixed amount of 20 wt % PALF in the form of short and fine fibers were prepared with a laboratory twin screw extruder and then injection molded. The mechanical properties of three types of PALF, i.e. untreated, alkaline- and silane-treated, were studied. Significant improvements in modulus and heat distortion temperature were obtained. The crystalline structure and orientation in the injected composites were investigated with synchrotron wide angle x-ray scattering (WAXS). It was found that both PALF and nylon crystallites oriented well along the flow direction and this is the key factor for the improvements observed.     

基于全矢量显式算法注射填充软件的研究与开发

基于前人模拟注射填充的显式算法,提出了一种新的全矢量化运算显式算法。对于各类注射填充的模拟,此算法避免了压力场的全局求解,矩阵操作仅在单元一级进行,通过反馈修正,在各时间增量步使已填充的区域满足不可压缩条件。由于避免了所有的全局耦合求解,计算代价与节点的自由度近似成正比,可实现填充模拟过程的高效运算。由于矢量化算法是完全脱耦的,容易实现并行计算。基于这种新算法,应用有限元法进行了注射填充仿真软件的初步开发。其填充模拟结果与商业软件MOLDFLOW的三维模拟结果比较,证实了该软件的有效性。     

Calculation of residual stresses in injection molded products

Both flow- and thermally-induced residual stresses which arise during the injection molding of amorphous thermoplastic polymers are calculated in the filling and post-filling stage. To achieve this, a compressible version of the Leonov model is employed. Two techniques to calculate flow-induced residual stresses are investigated. First, a direct approach is developed where the pressure problem is formulated using the viscoelastic material model. Second, generalized Newtonian material behavior is assumed in formulating the pressure problem, and the resulting flow kinematics is used to calculate normal stresses employing the compressible Leonov model. The latter technique gives comparable results, while reducing the computational cost significantly.     

Elastic flow-front fingering instability in flowing polymer solutions

An experimental investigation of the flow-front behavior of dilute and semi-dilute polymer solutions has been carried out to gain a better understanding of the underlying mechanisms leading to the occurrence of an unstable flow at the advancing flow-front during the filling of a rectangular Hele-Shaw cell. Our experimental results have revealed the existence of an elastic finger-like instability at the advancing flow-front that develops in semi-dilute solutions of high molecular weight polymers, with an onset time of approximately a few hundred milliseconds. Although at shear rates above critical, narrow finger patterns develop at the flow-front, their amplitude and number remain roughly constant throughout the flowing. At critical condition, no secondary flow was observed in the vicinity of the front region where the unstable flow develops. Transient response of the normal stress difference and the shear stress in the plate-and-plate geometry at shear rate above critical (for the elastic fingering instability in the Hele-Shaw cell) did not reveal any anomalous that could lead to the formation of such finger-like instabilities. These instabilities were observed for both the ideal elastic Boger fluids and shear thinning viscoelastic fluids.     

Bildung orientierter Randschichten in Spritzgußplatten aus Polypropylen

Zusammenfassung An 2 mm dicken unter verschiedenen Bedingungen spritzgegossenen Platten aus zwei Polypropylentypen mit unterschiedlicher Molmassenverteilung wird durch Messung der optischen Doppelbrechung die Dicke der hochorientierten Randschichten bestimmt. Durch solche Messungen an Platten, die mit und ohne Nachdruck gespritzt wurden, lassen sich die während der Füllphase von den während der Nachdruckphase entstandenen Orientierungsanteilen trennen. Möglichkeiten der theoretischen Berechnung der Randschichtdicke werden diskutiert.Hieraus ergibt sich, daß die hochorientierten Randschichten bereits während des Füllvorganges entstehen und deren Dicke vermutlich durch die Konkurrenz zwischen scherinduzierter Kristallisation und Relaxation bestimmt wird. Beim Spritzen ohne Nachdruck kann die Schmelze in der Mitte der Platte zwischen den Randschichten relaxieren und stark unterkühlt werden, bevor sie kristalliert, wie durch zusätzliche Messungen nachgewiesen wurde.

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The thickness of highly oriented skin layers is determined on 2-mm-thick plates injected under different processing conditions by birefringence measurements. Two technical polypropylene types of different molar mass distributions are used. Measurements on samples injected with and without pressure hold after filling make it possible to decide between chain orientation caused during injection and chain orientation caused by the pressure hold after filling. Different models for the calculation of the oriented layer thickness are discussed.The results reveal that the highly oriented skin layers are already formed during the filling phase and that thickness is probably determined through the opposing development of stress-induced crystallization and relaxation. Further measurements indicate that at the injection molding without pressure hold after filling, the melt can relax between the skin layers and can be strongly supercooled before it crystallizes.

Erweiterte Fassung eines Vortrages anläßlich des Hamburger Symposiums Rheologie makromolekularer Stoffe, 18.–22. 9. 1986     

注塑成型充填／后充填过程统一的可压缩流动分析

注塑成型是重要的塑料成型工艺,成型过程中熔体在模腔中的流动和传热对最终制品的性能和质量有重要的影响,因此,精确预测注塑过程的流动及传热历史,并进一步预测注塑制品的收缩、翘曲和机械性能等性能和质量指标具有重要意义。为了精确地描述成型过程中材料的流动及传热行为,本文针对注塑成型过程的工艺特点,将充填后充填过程作为一个统一的过程,考虑材料可压缩性及相变对充填和后充填过程的影响,建立了充填后充填过程的统一数学模型。采用有限元/有限差分/控制体积混合数值方法,实现了注塑成型充填后充填一体化模拟。数值模拟结果与实验结果的对比,验证了本文模型和算法。