A Primer on Glass Fiber Reinforcements

Bundle tex is a term used for products like multi-end rovings, continuous filament mat and chopped strand mat. These products are composed of a series of very low tex bundles of glass designed to stay in their discrete bundles rather than filamentize and completely disperse. Staying in these bundles improves strength and tear resistance. A completely dispersed product, such as a veil, improves surface appearance. Smaller bundle tex offers less “print through.” Higher bundle tex provides better strength and tear resistance. Chemistry Applied to Glass Reinforcements After determining the product form that fits the applicable molding process, the next step is to ensure that the proper chemistry has been applied to the reinforcement so that it will bond with the resin. Two important concepts related to chemistry are sizing and binder. These terms are not interchangeable. In the glass reinforcements industry, the term sizing is used in a slightly different way than in the traditional textile industry. Sizing is a microscopic layer of chemicals applied to every single glass filament as it exits the furnace. The sizing system is arguably the most important choice after selecting the product form. Sizing applied to the fiber:

• Protects it during the reinforcement manufacturing process
• Protects it during the fabrication process
• Provides the preferred interface with the appropriate organic or inorganic matrix (most often resin)

All glass reinforcements have sizing to prevent the fibers from self-destruction. The sizing is the interface between the glass and the resin. It facilitates bonding of the two so that load can be transferred and shared in the composite structure. Commonly used resin matrices are unsaturated polyester, vinyl ester, epoxy, polyurethane and phenolic resin.