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     

Predicting molding forces during sheet molding compounds (SMC) compression molding. II: Effect of SMC composition

One of the fastest‐growing applications of SMC compression molding is the manufacture of truck body panels. Because of their large size, the molding forces required are substantial and have a major influence on the molding cycle. Also, as SMC moves towards parts requiring higher strength, the fiber length and percentage by weight of fibers must increase. This will also contribute to larger molding forces. In this paper, a procedure is presented to evaluate the SMC rheological parameters needed to predict molding forces. In addition, the effect of SMC composition on the molding forces is investigated. In particular, we evaluate the effect of reinforcement type (glass versus carbon) and level, filler level and thickener level. It was found that the factors most affecting molding forces are the reinforcement length and level; and the filler level. In addition, it was discovered that for SMC thickened with magnesium oxide, the level of thickener does not affect the molding force.     

Multifunctional high density polyethylene nanocomposites produced by incorporation of exfoliated graphite nanoplatelets 1: Morphology and mechanical properties

This research explores the potential of using exfoliated graphite nanoplatelets, xGnP, as the reinforcement in high density polyethylene (HDPE). Two kinds of xGnP nanoparticles were used; xGnP‐1 has the thickness of 10 nm and a platelet diameter of 1 μm, whereas xGnP‐15 has the same thickness but the diameter is around 15 μm. HDPE/xGnP nanocomposite were fabricated first by melt blending and then followed by injection molding. The HDPE/xGnP nanocomposite's flexural strength, modulus and impact strength were evaluated and compared with composites filled with commercial reinforcements such as carbon fibers (CF), carbon black (CB) and glass fibers (GF). Polymer nanocomposites from HDPE/xGnP are equivalent in flexural stiffness and strength to HDPE composites reinforced with glass fibers and carbon black but slightly less than that of HDPE/carbon fiber composites at the same volume fraction. However, the Izod impact strength of HDPE/xGnP nanocomposites is significantly greater (∼250%) than all other reinforcements at the same volume fractions. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

SMC轻量化初步探究

为实现SMC轻量化,通过模压工艺,从原材料选型、配方设计以及工艺过程控制三个方面对轻质SMC(片状模塑料)进行了探究。首先,通过研究不同类型中空玻璃微珠(HGS)对制品比重、光亮度以及弯曲强度的影响发现,VS5500和H40适合作为轻量化SMC轻质填料,制品的设计密度和真实密度比较接近,且力学性能损失较小。其次,通过配方设计,研究了中空微珠用量、增稠剂类型以及增稠剂用量对制品比重的影响。同时研究了玻纤含量和树脂类型对制品力学性能的影响。研究结果表明,轻质SMC的设计密度不能过低,否则制品中HGS的破损比例将会增加。研究发现EK100作为增稠剂,树脂糊前期粘度可以有效控制,后期粘度快速上升,可以有效防止中空微珠相分离的发生。此外,随着玻纤含量从25%增加到30%,制品力学性能呈现增加趋势,弯曲强度从148 MPa增加到172 MPa,但随着玻纤进一步提高,弯曲强度反而出现大幅度衰减,降到140 MPa。通过研究三种不同类型树脂对制品外观和力学性能的影响,使用P18-03树脂压制的制品外观最好,其弯曲强度为172 MPa,满足汽车外饰件力学性能要求。最后,通过工艺过程控制,研究了微珠处理工艺对制品比重的影响。结果表明,烘干处理的HGS可以有效降低树脂糊的水含量,从而保证树脂糊后期粘度可以达到适合模压的窗口。     

Void formation and transport during SMC manufacturing: Effect of the glass fiber sizing

The present study investigates the origin of voids in sheet molding compounds (SMCs) sheets and their transport during the manufacturing steps. Paste mixing, impregnation, thickening, and molding have been performed with five different SMC sheets, one without fibers and the others with four different types of glass fiber bundles. The fiber surface energy and bending rigidity were quantified, together with the paste surface energy. Void content was then measured at each manufacturing step. Two main void origins in SMC sheets have been observed: (i) air entrapment during paste mixing and (ii) poor bundle impregnation. These voids may be largely removed during SMC manufacturing. The quality of impregnation and void elimination during the flow is found to depend on the bundle characteristics (rigidity and surface energy) conferred by their sizing and over sizing. POLYM. COMPOS. 27:289–298, 2006. © 2006 Society of Plastics Engineers     

Air entrapment in sheet molding compounds (SMC)

Entrapped air can commonly lead to large delaminations in thick walled sheet molding compound (SMC) products. In this work different sources of air entrapment in SMC are investigated. The critical process is shown to be the impregnation of the fibers. If no surface active additives are used, large volumes of air may be entrapped in this process, unless the viscosity of the compound is very low. In this situation of poor wetting, the viscosity of the compound during fiber impregnation will critically determine the interlaminar, tensile strength of the product. However, if surface active additives are used, the air escapes entrapment even at relatively high viscosities. The lowering of the viscosity, which is a side effect of the additives, has practically no importance under these conditions of good wetting. Large numbers of small air bubbles are also entrapped during the mixing of the components, but it is shown that these bubbles have very little effect on the mechanical properties of the finished part.     

成型助剂对高效氨复合吸附剂强度稳定性的影响

对CaCl2/SiO2体系高效氨复合吸附剂的成型开展研究。从提高成型吸附剂初始强度和改善成型吸附剂孔结构两方面进行实验,考察了不同助剂对吸附剂强度稳定性的影响。结果表明,在成型过程中,通过加入助剂玻璃纤维明显提高了吸附剂初始强度,当玻璃纤维添加量为CaCl2/SiO2体系质量7%时,吸附剂初始强度提高了75%,但吸附剂强度稳定性表现差。通过向粘结剂CMC-Na中引入助剂Al(NO3)3交联成型的吸附剂具有更好的孔结构,对于一定的CaCl2/SiO2体系,当Al(NO3)3与CMC-Na质量比为0.6时,吸附剂多孔性能达到最优,吸附剂强度稳定性得到明显提升,且氨吸附量提高,吸附性能稳定。     

The effects of molding conditions on the surface composition of sheet molding compound

An improved internal reflection infrared spectroscopy (ATR) technique (1) has been found to be effective for measuring the relative concentrations of polyester and polystyrene (resin) and calcium carbonate filler on sheet molding compound (SMC) surfaces. The technique has been used to determine the effect of molding conditions on the surface compositions of three commercial SMC materials. The surface compositions of two of the materials, of the same formulation but obtained from different sources, were the same and were unaffected by molding conditions. The surface of the third material (or a different formulation) was found to have substantially less resin than the first two materials. The surface composition of the third material varied with molding conditions, the greatest uniformity being obtained with high molding temperatures and pressures. This study has shown that the ATR technique is suitable for determining the relative surface compositions of SMC formulations. This method will be used to correlate the SMC surface composition to SMC properties, such as surface appearance, paintability, and adhesive bond durability.     

An evaluation of the curing characteristics of thermosetting epoxy carbon fiber sheet molding compounds and validation through computer simulations and molding trials

Sheet molding compounds (SMC) are ready-to-mold thermoset composite materials reinforced with discontinuous fibers, usually compression molded. Finite element (FE) based compression molding tools can be employed to optimize this process; FE tools require to define material models using raw material data measured through different characterization techniques. In this study, the cure kinetics of an epoxy-based carbon fiber SMC has been characterized by means of differential scanning calorimetry (DSC) and moving die rheometer (MDR) techniques. Based on these datasets, Claxton-Liska and Kamal-Souror models have been set and the compression molding of a validation plate was performed, both experimentally and virtually. The results indicate that, even if both characterization techniques are valid for SMC curing characterization, MDR technique enables the characterization of the material at real molding temperatures and the model based on MDR leads to more accurate results.     

Preferred orientation of chopped fibers in polymer-based composites processed by selective laser sintering and fused deposition modeling: Effects on mechanical properties

The orientation of reinforcing fibers in polymer-based composites greatly affects their mechanical features. It is known that different orientations of continuous fibers in the stacked layers of a laminate play a crucial role in providing an isotropic mechanical behavior, while the alignment of chopped fibers in injection molding of composites results in a degree of anisotropy. Recent additive manufacturing techniques have offered a way of controlling the fiber orientation. This article aims to investigate the effect of fiber orientation on the mechanical properties of polyamide/carbon fiber composites processed by fused deposition modeling and selective laser sintering. Tensile samples which had different fibers and layer interface with respect to the sample axis (and therefore to the tensile load) were produced. Tensile tests were performed at different strain rates; the tensile properties and the fracture surface morphology were correlated with the processing method and the sample microstructure. The best strength and stiffness were observed when the fibers and the layer interfaces were parallel to the sample axis.     

模压及其增强材料发展动向

综合分析了模压技术及模压材料的国内外发展情况,文中认为,SMC、BMC用玻璃纤维正向环保型方向发展,热塑性复合材料模压成型已成为当今发展热点之一,适合高强度、大型制件成型的高压树脂传递模塑(RTM)正逐步应用于汽车制造等产业。     

Characterization of composite tiles fabricated from poly(ethylene terephthalate) and micromarble particles reinforced by glass fiber mats

Polyester composite tiles (PCT) are synthesized from PET and fabricated by compression molding using micromarble clusters as filler. Three batches of marble clusters with different size distributions are used to assess the effect of particle size on mechanical properties. In addition, tiles are cured at 40, 60, 80, 100, and 120°C to characterize the dependence of mechanical properties on cure temperature. Tiles prepared using finer marble grades yield consistently higher flexural strength and stiffness values regardless of the cure temperature. The cure temperature does not seem to have an appreciable effect on mechanical properties except for 120°C cure. Samples cured at 120°C registered a sharp drop in mechanical properties. Dynamic mechanical analysis indicates improved material damping when coarse grade marble dust is used. Prospects of improving mechanical properties are explored by reinforcing PC tiles with randomly oriented, discontinuous glass fibers. This is achieved by placing a single layer of glass fiber mat on the top and bottom tile surface. Presence of fiber mats leads to the formation of a graded particle size distribution across the mat thickness when the coarse grade marble dust is used. This distribution resulted in significant improvements in flexural strength, stiffness, and overall toughness of the tiles by enhancing the interfacial region between the glass mats and the PC tile. The mechanism of improvement is elaborated by studying the crack propagation and fracture morphology. POLYM. COMPOS., 33:1921–1932, 2012. © 2012 Society of Plastics Engineers     

Variability in static strengths of sheet molding compounds (SMC)

In this paper, the variability in static strengths of six glass fiber-reinforced sheet molding compounds (SMC) is reported. This variability was shown not to be caused by macroscopic variations in fiber, resin, filler, or void content nor gross fiber anisotropy. Weibull statistics were used to accurately characterize this variability, Random flaw models with the flaws being distributed in the volume, surface, or edge were shown not to predict the observed static strength variability in SMC.     

Injection molding higher performance reinforced plastic composites

Conventional screw plasticizing injection molding machines (IMM) have been used to mold over 50 wt% of all reinforced plastics (RP) composite processed (1–9). Principal reinforcement used is E-glass of short glass fibers (SGF) with thermoplastics (TP) such as nylon (PA) and polypropylene (PP) (each over 25 wt% of total). Fiber lengths are usually limited to being milled to 1 mm (0.04 in); average length in molded parts are 0.3 mm (0.01 in) to 0.5mm (0.02 in); Long glass fibers (LGF) would be more desirable in obtaining better performances such as higher strength, stiffness, creep resistance, fatigue resistance and improvements in dimensional stability and thermal properties. However, fibers will degrade in length during conventional molding resulting in less efficient use of reinforcements. LGFs can start at 10 mm (0.4 in) and after IM can be in the order of at least 5 mm (0.2 in); longer fibers are also used. Special fiber impregnation techniques will permit successfully molding LGFs (1–21).     

FTIR and SEM analysis of polyester‐ and epoxy‐based composites manufactured by VARTM process

Polyester‐ and epoxy‐based composites containing glass and carbon fibers were manufactured using a vacuum‐assisted resin transfer molding (VARTM) process. Fourier transform infrared (FTIR) spectroscopy analyses were conducted to determine the interaction between fibers and matrix material. The results indicate that strong interaction was observed between carbon fiber and epoxy resin. However, weak interactions between remaining fiber‐matrix occur. Scanning electron microscopy (SEM) analysis was also performed to take some information about strength of interaction between fibers and matrix material. From SEM micrographs, it is concluded that the findings in SEM analysis support to that obtained in FTIR analysis. Another aim of the present work was to investigate the influence of matrix on composite properties. Hence, the strengths of composites having same reinforcement but different matrix systems in axial tension and transverse tension were compared. Short beam shear test has been conducted to characterize the interfacial strength in the composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphology and mechanical properties of unidirectional sisal– epoxy composites

Plant fibers are of increasing interest for use in composite materials. They are renewable resources and waste management is easier than with glass fibers. In the present study, longitudinal stiffness and strength as well as morphology of unidirectional sisal–epoxy composites manufactured by resin transfer molding (RTM) were studied. Horseshoe‐shaped sisal fiber bundles (technical fibers) were nonuniformly distributed in the matrix. In contrast to many wood composites, lumen was not filled by polymer matrix. Technical sisal fibers showed higher effective modulus when included in the composite material than in the technical fiber test (40 GPa as compared with 24 GPa). In contrast, the effective technical fiber strength in the composites was estimated to be around 400 MPa in comparison with a measured technical fiber tensile strength of 550 MPa. Reasons for these phenomena are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2358–2365, 2002     

高光表面SMC的研究

本文主要对高光表面SMC进行了研究.采用正交实验设计法对影响SMC表面光泽度的主要影响因素LPA、MgO、CaCO3和模压温度进行了系统的探讨与分析,以SMC制品的表面光泽度和弯曲强度为参考值,得出了4因素对SMC制品表面光泽度的影响趋势曲线.综合表面光泽度和弯曲性能得到一组进一步优化的SMC配方,根据该配方所压制的SMC制品的表面光泽度可达到90,并具有较好的力学性能.     

Sheet molding compound characterization using spiral flow

Sheet molding compound (SMC) is a fiber‐reinforced polymeric composite. It is often used in automotive, marine, and industrial applications over other materials because of its high strength to density ratio, resistance to corrosion, and low cost. There is a demand in the SMC industry to be able to characterize SMC processability. This is particularly true for heavy truck body panels, one of the fastest growing applications of SMC. Because of their large size and high strength requirement, the molding forces have a major influence in the molding cycle. Also because of the long flow paths involved, the ability of the paste to carry glass needs to be properly characterized when developing new SMC materials. In this article, we demonstrate the benefits of using spiral flow as a processability tester. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Jute fiber reinforced polypropylene produced by continuous extrusion compounding,part 1: Processing and ageing properties

This article addresses the processing and ageing properties of jute fiber reinforced polypropylene (PP) composites. The composite has been manufactured by a continuous extrusion process and results in free flowing composite granules, comprising up to 50 weight percent (wt %) jute fiber in PP. These granules have similar shape and diameter as commercially available PP granules. Rheological analysis shows that viscosity of the compounds follows the same shear rate dependency as PP and is on the same level as glass‐PP compounds. The mechanical properties show very little variation and exhibit strength and stiffness values at the upper range of competing natural fiber reinforced compounds for injection molding. The mechanical performance reduces gradually upon prolonged thermal loading and immersion in water. The low water diffusion coefficient of the 50 wt % jute‐PP composites indicates that the fibers are not forming a continuous network throughout the polymer. The jute fibers exhibit a stabilizing effect against ultra violet irradiation (UV) on PP polymer and, as a consequence, the mechanical properties of jute‐PP composites hardly decrease during an accelerated UV ageing test. Bacteria, fungi, and garden mold grow easily on the compound material, but only have a limited effect on mechanical properties. The resistance to growth of bacteria on the materials surface can be increased using a biostabilizer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dynamic mechanical behavior of LCP fiber/glass fiber–reinforced LLDPE composites

Liquid crystalline polymer (LCP) fibers and glass fibers have been used to rein force linear low density polyethylene (LLDPE) by using an elastic melt extruder and the compression molding technique. The impact behavior of hybrid composites of different composition is compared and is explained on the basis of the volume frac tion of the fibers. Addition of glass fibers decreases the Izod impact strength LLDPE. The impact strength of the composites increases when glass fibers are placed by LCP fibers. Dynamic mechanical α and β relaxations are studied and effect of variation of fiber composition on these relaxations is reported in the tem perature range from −50 to 150°C at 1 Hz frequency, a relaxation shifts toward higher temperatures with addition of fibers in LLDPE. Addition of fibers increases the storage modulus of LLDPE.