Thermoset composites offer a number of benefits in end-use products, which is why they are increasingly used to replace metal and traditional plastics. With their strength-to-weight ratio, temperature and chemical resistance, durability, and more, thermosets are being used in products like wind turbine blades, aerospace materials, watercraft, automotive, electronics, and construction materials.
Thermoset composites are formed when two or more components – typically a polymer matrix (thermoset resin) and a reinforcing fiber – are mixed with each other under ambient conditions or when induced by radiation or heat to form a highly cross-linked network. The combination of a thermoset resin and reinforcing fiber makes them stronger and leaves them hard and rigid after curing to resist high loads.
In addition to fibers, fillers and pigments are components that can also be incorporated to deliver additional beneficial properties to thermosets. Pigments are typically used for aesthetics to provide color. Fillers can be used for more functional purposes, such as providing fire-retardant properties by using aluminum trihydrate (ATH) or to enable lightweighting by using glass bubbles. Fillers such as calcium carbonate can also be used to reduce cost by replacing part of the resin.
The challenge with processing thermoset composites comes with achieving high filler loading to maximize mechanical properties, flame retardancy and cost savings without impacting or interfering with curing or maturation, as well as achieving the highest color strength at the lowest possible pigment loading.
Small But Mighty Dispersants
Dispersants are used in small quantities in thermoset formulations, but they play an oversized role in improving the processing and final properties of the thermoset. Dispersants help in evenly distributing fillers and additives within the resin matrix. This uniform distribution is crucial for achieving consistent material properties throughout the composite and to reduce viscosity and prevent agglomeration. They help improve processability by enabling faster wetting and dispersion of particulates in the resin. They also enable lightweighting and improved fire safety, productivity and cost benefits by increasing filler and/or flame-retardant content.
Calcium carbonate is a widely used filler in thermoset applications which acts as an extender in fiberglass reinforced polyester applications like sheet molding compound (SMC) and bulk molding compound (BMC). Dispersants, like Solplus™ D540, enable higher loading of calcium carbonate to function as a cost-effective extender to improve mechanical properties without impacting processing. Similarly, for improved fire retardancy, dispersants enable the increased loading of ATH.
Testing Increased Filler Loading
In testing, Solplus™ D540 demonstrates its effectiveness at enabling increased filler loading with both calcium carbonate and ATH. For the three rheology results below, all fillers were dispersed in a UPE resin. Solplus™ D540 was tested at 1% of the weight of the filler in each case. The curves clearly show the impact of the dispersant in preventing large changes in viscosity, thus allowing higher levels of filler to be incorporated.
Lubrizol’s advanced plastic dispersants under the Solplus™ Hyperdispersants brand are highly effective aids for the dispersion of fillers and pigments by eliminating flocculation, reducing viscosity and stabilizing them with time. These properties allow for increased pigment/filler loadings and increased color strength while preventing re-agglomeration of particles. Solplus™ Hyperdispersants also reduce dispersion times (which reduces energy and labor costs and improves manufacturing efficiency) and enable formulators to have more flexibility and deliver excellent performance and quality.
In addition to dispersants, Lubrizol also offers a range of other additives suitable for use in thermoset composites, including air release agents, styrene suppressants and rheology control additives.
Contact us to learn more about how Lubrizol can help improve processing in thermoset composites through a variety of hyperdispersants and additives.
