Meaning
Protective layers on reinforcement fibers act as the bridge between the inorganic glass and the organic polymer matrix. The application of glass fiber sizing occurs during the fiber drawing process to prevent the delicate filaments from abrading each other or breaking during winding. This coating contains lubricants, film formers and coupling agents that are tailored to specific resin families.
Without this chemistry, the glass would remain a separate phase within the plastic, failing to provide any meaningful structural reinforcement.
Surface Treatment
Handling characteristics of the dry fiber are determined by the composition of the aqueous mixture. Effective glass fiber sizing ensures that the roving or chopped strands can be fed into an extruder without bird-nesting or creating excessive dust. The coating also protects the glass from moisture which can weaken the filaments over time.
Different chemistries are used for polyolefins compared to high-temperature engineering plastics to ensure compatibility with the processing temperatures.
Interfacial Strength
Load transfer between the resin and the reinforcement depends entirely on the bond created by the coupling agents. Within the glass fiber sizing, organosilanes react with the glass surface while providing sites for the polymer chains to anchor. This molecular connection allows the composite to resist tensile and impact forces.
A failure in the sizing chemistry leads to fiber pull-out where the glass slides through the matrix instead of reinforcing it.
Degradation Risk
Excessive heat or chemical incompatibility can strip the protective layer from the fiber. If the glass fiber sizing burns or decomposes during the molding process, the part will exhibit poor mechanical properties and potential discoloration. Contamination of the sizing can also lead to outgassing and porosity in the molded wall.
Selecting the correct grade of glass for the specific base resin is essential to maintaining the long-term durability of the component.
