Vinyl molding compounds: Formulation and performance evaluation

Today's vinyl molding compounds are successfully meeting the combined challenges of physical properties, appearance, processability, and cost requirements in a variety of specialty injection molding applications such as appliance parts, business equipment, and electrical enclosures. One of the major reasons why vinyl materials are so versatile is that the poly(vinyl chloride) resins on which they are based can be easily modified with a wide variety of additives to tailor the particular performance features of the compounds to their intended applications. Determination of an appropriate combination of PVC resin and additives to produce an effective and cost-competitive compound, however, is not a simple process. Important considerations in formulating a vinyl molding compound and evaluating its performance are discussed here.     

Injection molding PVC

Injection molding rigid PVC is no longer the chore it once was. Advances in resin properties, additive systems, and molding equipment have allowed injection molders to take advantage of PVC's favorable economic, weatherability, flame retardant, and chemical resistant properties. As a result, injection molding of PVC is entering a new era. With the proper equipment and formulations, today's PVC molder is graduating from pipe fittings to ever more profitable, yet demanding, parts and applications.     

氯乙烯-丙烯酸丁酯共聚树脂的性能优化及应用

通过调整生产工艺或聚合配方,对氯乙烯-丙烯酸丁酯共聚树脂(以下简称氯丙树脂)中丙烯酸丁酯的含量及分布,氯丙树脂的分子质量及其分布、颗粒特性、热稳定性进行了优化;比较了优化后的氯丙树脂与普通PVC树脂的加工性能和力学性能,并将其应用于PVC型材和注塑管件的生产。结果表明:①氯丙树脂中丙烯酸丁酯的质量分数以5%～10%为宜;②通过调整生产工艺或聚合配方,可制得丙烯酸丁酯分布均匀、分子质量分布集中、粒度分布集中、热稳定性优良的氯丙树脂;③氯丙树脂可提高PVC树脂的加工性能和力学性能,可部分替代ACR或CPE等助剂;④经氯丙树脂改性生产的PVC型材和注塑管件性能合格,可简化注塑生产工艺,提高碳酸钙的用量,从而降低产品成本。     

Effect of injection molding parameters on properties of cross-linked low-density polyethylene/ethylene vinyl acetate/organoclay nanocomposite foams

Injection molding of foam articles has always attracted much interest because of elimination of sink mark, good dimensional stability and reduced production cost. In this study, the nanocomposite samples based on low-density polyethylene/ethylene vinyl acetate/organo montmorillonite were processed into foams by injection molding method. Nanocomposites were prepared by co-rotating a twin-screw extruder. The experimental design was based on Box?CBehnken method and parameters such as injection rate, mold temperature and nanolayered silica content were examined in relation to physico-mechanical properties of foams using response surface methodology. Three levels of injection rate (30, 60 and 90?mm/s), nanoclay content (0, 3 and 6?phr) and mold temperature (160, 175 and 190?°C) were chosen. The mathematical model and response surface graphs were employed to illustrate the relationship between the variable parameters and foam properties. The results revealed that the cell size and cell density as the main characteristics of the foams were affected by all parameters. Cell density of samples was affected by mold temperature, injection rate and nanoclay content. At high level of nanocontent the increase of injection rate was accompanied by decreases in density. Tensile strength and specific compression modulus of samples passed through a maximum versus mold temperature due to competition between cross-linking reaction and cell growth. At high mold temperature and injection rate, the cell rupture occurred because of low viscosity of the compounds at these conditions.     

Flow and cure phenomena in liquid composite molding

Liquid molding processes including resin transfer molding (RTM) and structural reaction injection molding (SRIM) continue to attract attention due to their potential for high volume manufacture. This paper examines and compares the pressuare and temperature histories observed in mold cavities during impregnation, heating, and polymerization for both RTM and SRIM using polyester, vinyl ester, and polyurethane resins in combination with continuous strand mats. Experimental results are related to thermal, chemical and rheological effects. Factors which influence materials behavior and process control and the implications for mold design are discussed.     

Structural performance of vinyl ester resin compression molded high strength composites

During the past few years the automotive industry has shown increasing interest in evaluating reinforced plastic composites (R/PC) for structural parts. The selection of R/PC systems is limited by economics and performance criteria; such as the ability to withstand temperature extremes, fatigue or other specific criteria depending upon the part. High Strength Molding Compound (HSMC) appears to be a promising R/PC technology. These performance requirements have lead to the development of HSMC based on vinyl ester or polyester resins for compression molding of automotive structural parts. This paper discusses static and dynamic physical properties as they relate to formulation and environmental variables for compression molded vinyl ester resin high strength composites. Static property data on tensile and flexural strength and modulus; coefficient of thermal expansion and Poisson's ratio for vinyl ester resin systems with 1 in. randomly chopped glass fiber levels from 37 to 72 weight percent at temperatures from −20 to 302°F are presented.     

仿真研究聚丙烯流变性能对气辅注塑的影响

应用计算机仿真手段研究了不同聚丙烯在充模速度相同条件下的压力及锁模力变化规律。结果表明，气辅注癃民传统注塑相比，所需压力，锁模力均有显著降低，且聚合物熔体流动速率越小，气体注射后产生的压力降赵大，表明在生产中应尽可能选用高ＭＦＲ树脂以利于气辅注塑工艺。     

An economical way of using carbon fibers in sheet molding compound compression molding for automotive applications

The automotive industry is extremely cost sensitive. This is one of the main reasons why sheet molding compound (SMC) compression molding is the most popular fiber‐reinforced polymeric composites manufacturing method in this industry. SMC compression molding economics are better suited for the automotive industry than processes such as resin transfer molding or any of its variations. For automotive SMC molders to take advantage of the added stiffness provided by carbon fibers, as an alternative to the widely used glass fibers, the manufacturing process needs to be simplified as much as possible. In actual manufacturing of SMC it is not easy to combine glass fibers with carbon fibers; it will be a lot more convenient to combine SMC plies only with carbon fibers together with SMC plies with only glass fibers. This will also allow molders that will normally use only glass fibers‐based SMC to secure carbon fiber SMC from a separate supplier and use it only where it makes economic sense. The main purpose of this study is to investigate the relative improvement in physical properties that can be achieved by substituting glass fibers by carbon fibers in a per ply basis. POLYM. COMPOS. 27:718–722, 2006. © 2006 Society of Plastics Engineers     

Properties of rapid prototype injection mold tooling materials

Epoxy acrylate‐based sterolithography resins have been used successfully as tools for injection molding. Molds made out of these resins fail at distinct times: during the first injection of plastic; during the first part first ejection; during either injection or ejection, but after a certain number of parts have been produced, which can be compared to a fatigue process. This paper presents corelations between measured properties of stereolithography molds and injection molding processing conditions so as to understand and predict mold failure. The study focuses on two stereolithography resins (SL 7510 and SL 7510) and one epoxy‐based composite material used for the high speed machining of prototype molds (Renboard). Rapid tooling materials are studied in fatigue, tensile, and fracture at injection molding operating temperatures and at room temperature. Finally, a method to address failure of molds is proposed using the theory of fracture.     

Understanding the functions of acrylic processing aids in rigid PVC injection molding

Poly(vinyl chloride) (PVC) compound use is growing in specialty injection molding applications such as appliances, business equipment, and electrical enclosures. A key factor in determining the appearance and physical properties of the molded parts is the processability of the PVC compounds, which can be improved through the use of acrylic processing aids. Processing aids promote PVC fusion, modify the melt rheology, and/or provide lubrication. Some processing aid products are designed to serve one of these functions while others provide a combination of functions. Each of these functions and its major benefits in rigid PVC injection molding are described. Some guidelines for selecting appropriate processing aid products for applications are provided.     

玻纤增强酚醛注塑料的制备技术和性能

研究了玻纤增强酚醛注塑料制备过程中基质树脂的选择、固化作用与交联结构的控制及玻纤分散技术,考察了不同基质树脂制备的酚醛注塑料的固化成型结构形态和固化流变特性.进一步采用热固性与热塑性酚醛树脂相复配的基质树脂体系,经配方和制备工艺的优化,制备了高填充量玻纤增强酚醛注塑料.该注塑料具有良好的注塑成型性能,注塑制品具有高强度, 冲击强度达到4.3 kJ•m^-2,弯曲强度137.4 MPa,同时热变形温度为 245 ℃,阻燃性通过美国UL 94 V-0级认证,并具有优良的尺寸稳定性、电绝缘性能和低成本优势.     

薄壁注塑透明聚丙烯专用料的结构与性能分析

对市场上常见的4种薄壁注塑透明聚丙烯专用料的熔融结晶性能、光学性能、分子量分布、力学性能、毛细管流变性能、热收缩性能等进行对比分析。结果表明，K4860H与其他3种透明聚丙烯专用料相比分子量分布最窄；K4860H相对于其他3种透明聚丙烯专用料具有更好的韧性和透明性；相对其他2种透明聚丙烯，K4860H和MT45S具有更高的结晶温度和更快的结晶速率，表明其具有更为优良的结晶能力；4种透明聚丙烯样品的黏度随剪切速率的变化规律相同，表明其具有相同的加工流变性能；K4860H和500B 2个方向的模塑收缩率接近，说明其具有良好的尺寸稳定性；基于以上对比分析可知K4860H主要性能指标优于对比的3种聚丙烯专用料。     

PVC degradation during injection molding: Experimental evaluation

This paper focuses on experimental observations of poly(vinyl chloride) (PVC) degradation during injection molding. Degradation of poly(vinyl chloride) has been extensively studied. These studies have been performed in quiescent systems with very little or no strain applied to the sample. However, during processing, the polymer experiences very large deformations, in particular in the case of injection molding. This work demonstrates that the large shear during injection molding causes a significant increase of degradation as compared to studies in quiescent systems. It was also observed that degradation occurs in less than 1/10 the time required for quiescent systems. Finally, the flow geometry also affects the degradation behavior during processing. Understanding the parameters leading to degradation could lead to schemes to avoid it. J. Vinyl Addit. Technol. 10:17–40, 2004. © 2004 Society of Plastics Engineers.     

Influence of Recycled ABS Added to Virgin Polymers on the Physical,Mechanical Properties and Molding Characteristics

Reuse of recycled polymers is steadily increasing. In this study, two different ABS virgin materials are considered. Then, blends of varying proportions of ABS recycled resins (0–50%), obtained from the gate and runner materials of products, was added to virgin resin to investigate the effect of various compositions of virgin ABS and recycled polymers on the physical and mechanical properties of the final blend. Three different rib and closure organization of boss of the reinforcement structures were designed and injection molded under blends of varying proportions of the ABS recycled resins to do the torsion test by Air-Torsion tools. In addition, molding characteristics were also examined. The results show that there is no obvious effect of recycled ABS percentage (by weight) on the tensile strength, elongation at yield, flexural strength, flexural modulus, and impact strength. However, the torsion strength for rib and closure organization of boss of the reinforcement structures decrease with increasing recycled ABS weight percentage. On the other hand, hardness, glass transition temperature, and melting flow index of recycled ABS increase with as the percentage (by weight) of recycled material increase. The impact strength was found to vary with the recycled ABS loading. The injection pressure decreases with increasing the content of recycled resin under some specified molding conditions.     

Microstructure and ultimate properties of injection molded amorphous engineering plastics: Poly(ether imide) and poly(2,6-dimethyl-1,4-phenylene ether)

Specimens of two engineerig plastics i.e., poly(ether imide), PEI, and poly(2,6-dimethyl- 1,4-phenylene ether), PPE, were injection molded employing a 40t Van Dorn injection molding machine and industrial practices. The mold and melt temperatures and the injection speed were varied in a limited range which furnished acceptable samples. The density, birefringence, residual stress distributions, flexure and tensile properties, and crack development of the injection molded specimens were studied. Vacuum compression molded samples were also prepared to investigate the role played by the cooling rate in shaping microstructural distributions. The results revealed significant differences in the development of microstructure of the molded specimens of the two resins, which was related to rheology and molding conditions on one hand and to development of cracks and ultimate properties on the other hand.     

Low temperature cure of vinyl ester resins

Vinyl ester resins are well known for their versatility as a composite matrix. With the development of a promising room temperature molding technology, vacuum-assisted resin transfer molding, e.g. Seemann Composite Resin Infusion Molding Process (SCRIMP), the processability of vinyl ester resins at low temperatures has attracted considerable attention from the composite industry. The objective of this paper is to provide a better understanding of the reaction kinetics of this resin system at low temperatures. In this study, a differential scanning calorimeter (DSC) coupled with a Fourier transform infrared (FTIR) spectrometer was employed to measure the reaction profile of a vinyl ester resin with different promoter and styrene contents. A kinetic model based on the free radical co-polymerization mechanism was developed for simulating the reaction rates and conversions of styrene vinyl and vinyl ester vinylene groups. The model parameters were determined from several FTIR experiments under isothermal conditions. This model, in conjunction with heat transfer analysis, was able to successfully predict the temperature profiles during curing in two SCRIMP molding cases based on groove type resin distribution system.     

Oxygen permeation resistance of polyethylene,polyethylene/ethylene vinyl alcohol copolymer,polyethylene/modified ethylene vinyl alcohol copolymer,and polyethylene/modified polyamide–ethylene vinyl alcohol copolymer bottles

The oxygen permeation resistance of polyethylene (PE), polyethylene/ethylene vinyl alcohol copolymer (PE/EVOH), polyethylene/modified ethylene vinyl alcohol copolymer (PE/MEVOH), and polyethylene/modified polyamide–ethylene vinyl alcohol copolymer (PE/MPAEVOH) bottles was investigated. The oxygen permeation resistance improved significantly after the blending of ethylene vinyl alcohol copolymer (EVOH) barrier resins in PE matrices during blow molding; less demarcated EVOH laminas were found on the fracture surfaces of the PE/EVOH bottles. Surprisingly, the oxygen permeation resistance of the PE/MEVOH bottles decreased significantly, although more clearly defined modified ethylene vinyl alcohol copolymer (MEVOH) laminas were found for the PE/MEVOH bottles as the compatibilizer precursor contents present in the MEVOH resins increased. In contrast, after the blending of modified polyamide (MPA) in EVOH resins, more demarcated modified polyamide–ethylene vinyl alcohol copolymer (MPAEVOH) laminar structures were observed in the PE/MPAEVOH bottles as the MPA contents present in the MPAEVOH resins increased. In fact, with proper MPAEVOH compositions, the oxygen permeation resistance of the PE/MPAEVOH bottles was even better than that of the PE/EVOH bottles. These interesting oxygen barrier and morphological properties of the PE, PE/EVOH, PE/MEVOH, and PE/MPAEVOH bottles were investigated in terms of the free volumes, barrier properties, and molecular interactions in the amorphous‐phase structures of the barrier resins present in their corresponding bottles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2528–2537, 2004     

Vinyl—a new blow molding polymer

Vinyl is used in a wide range of applications, not only in packaging but also in construction, automotive, and other areas. Vinyl (polyvinyl chloride, or PVC) has maintained a significant presence in some markets for more than 30 years. Yet vinyl is not necessarily on the downward leg of its product life cycle. New, more effective PVC blow molding compounds are being developed and introduced. These versatile new polymers are extending the life cycle of vinyl packaging into the 21st century. The long-standing success of vinyl in bottle applications is due to a number of key properties, including its chemical resistance, UV stability, low mold costs, design flexibility, low permeability, and aesthetics. In recent years, improved PVC compounds have created new growth markets for vinyl. Three important ones are hot-fill applications, personal care products, and bottled water. The potential of vinyl bottles to become a major factor in the fast-growing bottled water market is a particularly good example of the adaptability and versatility that make vinyl one of the most exciting “new” blow molding polymers.     

Epoxy Resins from 1980 to Date. Part 1

Epoxy resins are essentially prepolymers that contain on an average two or more epoxide groups per molecule. The object of the present review article is to give up-to-date information regarding the reactions of these resins with various curing agents leading to crosslinked or thermoset resins with excellent strength, toughness, and chemical resistance. The end-use consumption of epoxy resins covers a broad range of applications such as adhesives, bonding, construction materials (flooring, paving, and aggregates), composites, laminates, coating, molding, and textile finishing. Recently these resins have penetrated into the aero- and spacecraft industry. It is expected that anybody engaged in industry or academic research will find enough material in this review to start work, and need not search the literature before 1990.