常压动态保压注塑自增强高密度聚乙烯的结构与性能

研究了常压动态保压注塑自增强高密度聚乙烯的结构和力学性能的关系,自增强高密度聚乙烯的抗张强度和杨氏模量分别从原来的23MPa和1.0GPa提高到93MPa和5.0GPa。DSC、TEM和X射线衍射研究结果表明:力学性能的显著改善主要归因于串晶的产生、高分子链沿流动方向的轴取向和结构更加完善的球晶的生成。和高压保压法相比,本法具有现实的工业应用前景。     

Synergic Enhancement of High-density Polyethylene through Ultrahigh Molecular Weight Polyethylene and Multi-flow Vibration Injection Molding: A Facile Fabrication with Potential Industrial Prospects

General-purpose plastics with high strength and toughness have been in great demand for structural engineering applications. To achieve the reinforcement and broaden the application scope of high-density polyethylene(HDPE), multi-flow vibration injection molding(MFVIM) and ultrahigh molecular weight polyethylene(UHMWPE) are synergistically employed in this work. Herein, the MFVIM has better shear layer control ability and higher fabrication advantage for complex parts than other analogous novel injection molding technologies reported.The reinforcing effect of various filling times and UHMWPE contents as well as the corresponding microstructure evolution are investigated.When 5 wt% UHMWPE is added, MFVIM process with six flow times thickens the shear layer to the whole thickness. The tensile strength and modulus increase to 2.14 and 1.39 times, respectively, compared to neat HDPE on the premise of remaining 70% impact strength. Structural characterizations indicate that the enhancement is attributed to the improvement of shish-kebab content and lamellae compactness, as well as related to the corresponding size distributions of undissolved UHMWPE particles. This novel injection molding technology with great industrial prospects provides a facile and effective strategy to broaden the engineering applications of HDPE materials. Besides, excessive UHMWPE may impair the synergistic enhancement effect, which is also reasonably explained.     

Foamed crosslinked LDPE/PP blends made by hot mold injection molding

Foamed and crosslinked blends of LDPE and i-PP were investigated. The specimens were made by hot mold injection molding process at the temperature of the mold of 210°C. Azodicarbonamide as foaming agent and 2,5-dimethyl-2,5-di(tert.-butylperoxy)hexane as crosslinked agent were used. The chemical changes as a result of the crosslinking were determined by gel content. Thermal behavior of the blends was studied by DSC. The difference of influence of crosslinking agent on chemical changes of both polymers was established. An improvement of the mechanical properties due to crosslinking between PE and PP on their interface was observed. The interaction on the PE/PP interface was confirmed by phase transition parameters determined on the basis of DSC-curves.     

双环戊二烯反应注塑

作为一种新型工程材料,近年来聚双环戊二烯(polydicyclopentadiene, PDCPD)的研究备受关注。PDCPD多采用反应注塑成型工艺,需要在反应前有足够的储存稳定期以保证物料的混合和注模。本文介绍了不同催化体系的优缺点,着重阐述了极具应用前景的新兴Grubbs潜伏型催化剂最新进展,包括热触发型、化学触发型和光触发型等,并对其结构、性能及反应机理进行了详细分析。同时,围绕配体结构对催化特性的影响,对如何提高催化剂的潜伏性且保持其催化活性进行了对比和剖析。其中,螯合结构和O、S、N等杂原子基团的引入,提高了催化剂的潜伏性,但催化活性会有一定程度的下降。此外,还评述了聚双环戊二烯改性方面的相关研究,并对聚双环戊二烯产业发展的趋势进行了展望。     

几种采用熔体注射成型实现聚合物自增强的方法

对当前常用的几种注射自增强方法进行了归纳和总结介绍了高压注射法、拉伸流动法和剪切控制法等几种实现单向自增强的方法以及注射压制二步法、摆动注射法、旋转注射法和剪切控制法等实现双向自增强的方法。     

The Facility and Process Technics of Polyethylene Rotational Molding

1. Introduction Rotational molding is the process by which hollow plastic parts are formed. It mainly processes the product which Injection molding and Blow molding can not process medium-sized, large-sized and super large-sized plastic parts. The technics may turn out a tub, dustbin, stock tank, sailboat. The research institute of Lanzhou introduces a suit of RS-16 Rotational Molding Machine from Germany Reinhadt Co. on 1990. It mainly put up experiment and smallscale production. RS-16 rotational molding machine is a single arm and di-axial equipment. It is consisting of a gas heated sintering oven, cooling chamber, mouldcarrying carriage and a controlling unit.     

Control of Nano-Scale Structuring and Reinforcement in Rotational Molding of Polyethylene

Polyethylene (PE) resins used for Rotational Molding have usually particle sizes less than 0.8 mm and used as powders or micro-pellets. During heating in a rotating mould, these particles get fused and merge into one piece. A disadvantage of the rotomolding process is long cycle times that affect the production rate and increase thermal degradation of the polymer. One of the problems in rotomolding is bubbles of gasses trapped during sintering of the PE powders which reduce mechanical strength of the article produced. We propose to use reacting mixtures of PEG with citric acid as Processing Additive (PA) to rotomolding grades of PE. Silica fume and vinyl-silanes can be other ingredients of the additive package. The PA accelerates sintering of the PE particulates and greatly reduces number of bubbles in the melt but at high concentrations it impedes flow of the particles. Powders are characterized by low flowability while micro-pellets have too high flowability for rotomolding. To improve the rotomolding process we propose to fabricate micro-pellets by extrusion of PE resins comprising the PA at reduced temperatures and pelletizing in open air. The same PA reduces extrusion pressure and suppresses flow instabilities during pelletizing as well as adjusts flowability of micro-pellets to optimum, accelerates sintering of the PE particulates and removes bubbles from the PE melt. Mechanisms of the observed improvements are discussed.     

Enhanced Bone Defect Repair by Polymeric Substitute Fillers of MultiArm Polyethylene Glycol‐Crosslinked Hyaluronic Acid Hydrogels

Bone regeneration is still one of the greatest challenges for the treatment of bone defects since no current clinical approach has been proven effective. To develop an alternative biodegradable bone graft material, multiarm polyethylene glycol (PEG) crosslinked hyaluronic acid (HA) hydrogels are synthesized and applied to promote osteogenesis of mesenchymal stem cells (MSCs) with the ultimate goal for bone defect repair. The multiarm PEG‐HA hydrogels provide a significant improvement of alkaline phosphatase (ALP) activity and calcium mineralization of the in vitro encapsulated MSCs under osteogenic condition after 3, 7, and 28 days. In addition, the multiarm PEG‐HA hydrogels also facilitate healing of the cranial bone defects more effectively in a Sprague Dawley rat model after 10 weeks of implantation based on histological evaluations and microcomputed tomography analysis. These promising results set the stage for the development of innovative biodegradable hydrogels to provide a more effective and versatile treatment option for bone regeneration.     

二次注射成型聚丙烯中剪切诱导连接界面的形态演变

研究了剪切作用对二次注射成型聚丙烯连接界面形态演变的影响.利用偏光显微镜研究了连接界面距离浇口不同区域和不同位置的形态差异,探索了连接界面形态的演变规律,通过改变注射压力和注射速度对其加以验证,并通过DSC分析证实了形态结构的差异.研究表明:剪切作用对连接界面形态的影响显著,在高剪切作用下分子链沿流动方向取向程度高,不利于其规整排列并沿垂直界面方向生成横晶;可以通过注射压力和注射速度来控制连接界面的剪切作用,从而得到具有完善横晶结构的连接界面形态.     

Effect of Atomic Oxygen on the Surface Morphology of Polyethylene

The chemical species created in a low-pressure electrical discharge in oxygen attack the polymer at the surface, converting it to gaseous products. This process is interesting because: 1) the chemical changes on the resulting surface facilitate the formation of strong adhesive bonds and provide sites for the chemical attachment of other molecules, 2) significant morphological features lying below the surface may be revealed, 3) polymer can be cleanly removed from surfaces which are resistant to oxidation, and 4) dielectric breakdown frequently is preceded by the attack on the polymer of chemical species created in a corona discharge. Atomic oxygen is an important chemical species created in such a discharge. It reacts with organic substances rapidly at room temperature, but lives long enough in the low-pressure gas that it can be separated from many other reactive species created in the discharge. “Titration” with NO₂ provides a straightforward chemiluminescent means for determining the concentration of atomic oxygen to which the sample is exposed. This paper characterizes the attack of atomic oxygen, perhaps in the presence of long lived but less reactive species such as excited O₂molecules, on polymer surfaces, using electron microscopic observations of known morphological features of polyethylene to observe the changes produced by atomic oxygen. Lamellar polyethylene crystals were attacked both at the edges and the fold surfaces. Layers many microns thick were removed from spherulitic samples and replicas obtained from the surfaces thus exposed. Thick samples were thinned to the point at which they were transparent to an electron beam and interior morphological features were directly observed.     

茂金属支化聚乙烯的结构、形态与熔融行为

综述了茂金属支化聚乙烯的形态，结构和熔融行为，详细讨论了支链大小和含量以及分子量对其物理性质的影响。     

Response of Linear,Branched or Crosslinked Polyethylene Structures on the Attack of Oxygen Plasma

Linear, branched and crosslinked polyethylenes (PE) were exposed to the low-pressure oxygen plasma for 2–120 s. In the following the samples were washed with solvents to remove low-molecular weight oxidized material and to excavate the subjacent polymer structure for microscopic characterization. X-ray photoelectron spectroscopy (XPS) measurements provided information about changes in elemental composition and chemical structure of PE after plasma exposure and washing. The calculation of the concentration of tertiary C atoms using XPS data was a measure of branches and crosslinking in the polymer before and after exposure to oxygen plasma. Linear PE was most sensitive towards oxygen plasma and showed the highest concentration in tertiary C atoms after plasma exposure. On the other hand branched PE types, which possess originally more tertiary carbon atoms, have lost two-third of them after 2 s oxygen plasma exposure. Branched PE show also topological changes at their surface as detected by atomic force microscopy. Differential scanning calorimetry measurements confirmed strong changes in crystallinity and molecular orientation of linear PE already after 120 s exposure to the oxygen plasma interpreted as amorphization. These effects should be interpreted as result of crosslinking caused by the recombination of dangling bond sites.     

Investigation and Modeling of Temperature Dependence Recovery Behavior of Shape‐Memory Crosslinked Polyethylene

Shape memory was induced in crosslinked low‐density polyethylene by a heating‐stretching‐cooling cycle. The effect of crosslink content on thermal properties and temperature dependence recovery behavior was studied experimentally. The importance of stretching temperature and crosslink content on recovery behavior could be reasonably explained by the observed changes in the thermal properties which were attributed to the differences in crystalline structures and mechanism of crystal formation during the heating‐stretching‐cooling process. A mechanical model was developed to describe qualitatively and quantitatively the temperature dependence recovery behavior of the prepared shape memory crosslinked polyethylene at nonisothermal state under various conditions by driving constitutive equations using a set of model constants. These model constants were determined with the help of a set of optimization codes using a genetic algorithm method. By choosing a suitable set of model constants one can describe with high accuracy the temperature dependence recovery behavior of any shape memory polymer.

     

Photopolymers for Rapid Prototyping of Soluble Mold Materials and Molding of Cellular Biomaterials

To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers. These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials. Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials prepared by 3D-photoshaping.     

Photopolymers for Rapid Prototyping of Soluble Mold Materials and Molding of Cellular Biomaterials

Summary. To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers. These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials. Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials prepared by 3D-photoshaping.     

Construction of Pre-Deformed Shapes for Rapid Tooling in Injection Molding

The major issues in the development of injection molding technology include the progress in CAE and the developments in tool design methodology such as rapid tooling. The applicability of rapid tooling in injection molding was examined using unbalanced cooling to analyze the warpage and shrinkage. Moldflow Plastics Insight simulation software was used for the deformation calculations with different mold thermal conductivities. It can be concluded that the decreasing mold thermal conductivity will dramatically increase the volumetric shrinkage and the warpage as well. Because of these effects, it is of fundamental importance to compensate for the shrinkage and warpage, so in the paper a new design methodology is suggested for rapid tooling, which is based on the pre-deformed model.     

线性低密度聚乙烯的结构、形态与热行为研究进展

介绍了近年来包括藏金属ＬＬＤＰＥ在内的线性低密度聚乙烯的结构、形态、结晶、熔融和物理性质等方面研究工作的最新进展。     

Morphology and properties of hollow-fiber membrane made by PAN mixing with small amount of PVDF

In this paper, the morphological structure and properties such as, miscibility, tensile strength, flux and retention ratio of hollow-fiber membranes manufactured by PAN mixing with small amounts of PVDF have been studied. The hollow fiber was made from a spinning solution composed of polymer (PAN : PVDF=10 : 0, 9 : 1, 7 : 3), additive (PVP, PEG-600) and solvent (DMAC) when immersed in water. The spinnability of blend polymer and the influences of blending on spinning technology have been observed; the morphology of membranes were examined by SEM. The blend membranes possess much higher flux than PAN membrane and fairly good retention ratio especially for the membrane made by PAN : PVDF=9 : 1.