Effects Of Low-profile Additives Research Articles

Effect of low-profile additives on the durability of adhesively bonded Sheet Moulding Compound (SMC)

The mechanical bonding properties and the failure behaviour of adhesively bonded SMC substrates were investigated under the aspect of the influence of low-profile additives on the durability of joints. For this purpose, three SMC materials with different amounts of polyvinyl acetate (PVAc) and saturated polyester were bonded with a structural and semi-structural adhesive and tested under cleavage peel test in reference condition and after thermal and hygrothermal ageing. In addition characterisations of the individual materials and their ageing effects were made. In principle, destructive testing of bonded SMC substrates showed a dependence on the used adhesive and the appearance of a type of fibre bridging. Depending on the PVAc content, different fibre tearing rates occurred. Thermal ageing led to post-crosslinking of the materials and increasing stiffness. Moreover, strong fibre tear-out appeared. Hygrothermal ageing in the SMC results in physical reversible plasticizing effects and chemical ageing by hydrolysis of the low-profile additives, presumed by performed DMTA tests. A weakened interface and disbonding failure phenomena occurred with increased PVAc content of semi-structural bonded specimens. Thus, in terms of adhesive bonding of SMC structures, a focus should be put on the type and quantity of low-profile additives used. The reduction of PVAc content led to the required quality of the joint with regard to the durability.

The effects of low-profile additives on shrinkage and mechanical properties of cultured marble materials

ABSTRACT Cultured marble is a blend of unsaturated polyester and calcium carbonate that is combined with pigments and additives to produce a wide range of colours and realistic, natural-looking patterns. This study aims to investigate process conditions (catalyst, temperature, cured time, etc …) of cultured marble at high temperatures. The optimized process conditions are obtained by thermal analysis from DSC with a temperature of 110°C and curing time of 20 min, respectively. The optimum catalyst for process conditions in a bulk moulding compound (BMC) machine is 2 phr of benzoyl peroxide (BPO). The styrene amount in UP resin is determined at 37.40% by the Gas chromatography-mass spectroscopy – headspace (GCMS-HS) technique. Anhydride maleic (MA) is found to improve outstanding mechanical properties in terms of flexural properties, the strength of impact, and the resistance of volume shrinkage of UP resin in cultured marble material.

Effect of low-profile additives on thermo-mechanical properties of glass fiber-reinforced unsaturated polyester composites

Low profile additives (LPA) are thermoplastics particles incorporated into unsaturated polyester (UP) resin in order to improve the surface finish of fiber glass/UP composites by shrinkage compensation. They are widely used in automotive applications where high-quality surface finish is required. In this article, the effect of low-profile additives on the thermo-mechanical properties of resin transfer molded fiber glass/UP panels is investigated. A combination of poly vinyl-acetate and poly methyl-methacrylate additives was tested with three concentrations (0%, 10%, and 40%). The flexural and shear properties were measured by three-point bending and short-beam tests. Thermo-mechanical and dynamic mechanical analyses were performed to measure the coefficient of thermal expansion and the glass transition temperature. The mechanical properties as well as the coefficient of thermal expansion were reduced upon addition of low-profile additives, whereas the glass transition temperature was improved with the content of low profile additives due to a better compatibility of the LPA/UP system.

Optimization of RTM processing parameters for Class A surface finish

Resin transfer moulding (RTM) has the potential to become an efficient and economical process for manufacturing large automotive composite parts. For body panels, the material and processing parameters must be optimized in order to achieve a Class A surface finish. In this work, the Taguchi method was used to investigate the effect of low profile additives, injection pressure, temperature gradient, filler content, styrene content and gel time on the surface finish of glass fibre polyester composite panels. The low profile additives (LPA) concentration, mixed in with the resin to compensate for its chemical shrinkage, was found to be the most influential parameter affecting surface roughness and waviness. More samples were subsequently moulded under the corresponding optimum processing conditions for validation and variability assessment.

Cure shrinkage characterization and modeling of a polyester resin containing low profile additives

Resin Transfer Moulding (RTM) has great potential as an efficient and economical process for fabricating large and complicated composite structural components. The low capital investment cost required and process versatility in component integration and assembly make RTM very attractive for high volume automotive applications. One of the challenges facing the automotive field is the resulting surface finish of manufactured components. The shrinkage associated with the curing of thermoset resins contributes to the poor surface quality. Low profile additives (LPA) are added to the resin to compensate for the cure shrinkage; however their effects on the thermal, rheological and morphological properties of polyester resins are not well understood. In this paper, the effect of LPA on cure kinetics, cure shrinkage and viscosity of a polyester resin is studied through differential scanning calorimetry (DSC) and special rheological techniques. Models are developed to predict cure shrinkage, LPA expansion, cure kinetics and viscosity variations of the resin as a function of processing temperature. Finally, morphological changes in the resin with and without LPA, during isothermal cure, are studied with hot stage optical microscopy. The results show that the LPA content in the range tested had no significant effect on the cure kinetics. However, higher LPA content reduced cure rate and cure shrinkage. A minimum of 10% LPA was required to compensate for cure shrinkage. Shrinkage behavior of all formulations was similar until a degree-of-cure of 0.5. However, resin formulations with higher LPA content showed expansion at later stages during curing.

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. I. Miscibility, curing behavior, and glass‐transition temperatures

AbstractThe effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride), with different chemical structures and MWs on the miscibility, cured‐sample morphology, curing kinetics, and glass‐transition temperatures for styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems were investigated by group contribution methods, scanning electron microscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis, respectively. Before curing at room temperature, the degree of phase separation for the ST/UP/LPA systems was generally explainable by the calculated polarity difference per unit volume between the UP resin and LPA. During curing at 110°C, the compatibility of the ST/UP/LPA systems, as revealed by cured‐sample morphology, was judged from the relative magnitude of the DSC peak reaction rate and the broadness of the peak. On the basis of Takayanagi's mechanical models, the effects of LPA on the final cure conversion and the glass‐transition temperature in the major continuous phase of ST‐crosslinked polyester for the ST/UP/LPA systems was also examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3369–3387, 2004

The Effect of Low Profile Additives on Unsaturated Polyester Resins During Curing at Low/Medium Temperature: Shrinkage Behavior Study

The Effect of Low Profile Additives on Unsaturated Polyester Resins During Curing at Low/Medium Temperature: Shrinkage Behavior Study

Effects of poly(vinyl acetate) and poly(methyl methacrylate) low‐profile additives on the curing of unsaturated polyester resins. I. Curing kinetics by DSC and FTIR

AbstractThe effects of two low‐profile additives (LPA), poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) on the curing kinetics during the cure of unsaturated polyester (UP) resins at 110°C were investigated by using a differential scanning calorimeter (DSC) and a Fourier transform infrared spectrometer (FTIR). The effects of temperature, molar ratio of styrene to polyester CC bonds, and LPA content on phase characteristics of the static ternary systems of styrene–UP–PVAc and styrene–UP–PMMA prior to reaction were presented. Depending on the molar ratio of styrene to polyester CC bonds, a small shoulder or a kinetic‐controlled plateau in the initial portion of the DSC rate profile was observed for the LPA‐containing sample. This was due to the facilitation of intramicrogel crosslinking reactions since LPA could enhance phase separation and thus favor the formation of clearly identified microgel particles. FTIR results showed that adding LPA could enhance the relative conversion of polyester CC bonds to styrene throughout the reaction. Finally, by use of a microgel‐based kinetic model and static phase characteristics of styrene–UP–LPA systems at 25°C, the effects of LPA on reaction kinetics regarding intramicrogel and intermicrogel crosslinking reactions, relative conversion of styrene to polyester CC bonds, and the final conversio have been explained. © 1995 John Wiley & Sons, Inc.