Fiberglass Impregnating Agents: A Key Bridge Between Fiber Forming And Composite Material Interfaces (Part 2) Classification Of Impregnating Agents
In the fiberglass drawing process, sizing agents play an indispensable core role. These specialized treatment agents, coated on the surface of nascent fiberglasss, are key substances ensuring smooth fiber production, meeting subsequent processing requirements, and ultimately achieving excellent performance in composite materials.
Classification of Sizing Agents
Based on their main components, functional focus, and final application areas, fiberglass sizing agents are generally classified into three main categories:
1. Reinforcing Sizing Agents:
Core Objective: To maximize the reinforcing effect and interfacial properties of fiberglasss in composite materials (especially thermosetting and thermoplastic plastics).
Key Components: Centered on coupling agents (such as silanes), supplemented by film-forming agents (mostly reactive resins such as epoxy, polyester, and polyurethane emulsions), lubricants, antistatic agents, etc. Coupling agents are key "bridge molecules" connecting inorganic glass and organic polymers.
Characteristics: The coated precursor fibers (called "reinforcing precursor fibers") are typically stiffer and have good bundle properties. Mainly used for direct chopped strands, in SMC/BMC, winding, pultrusion, thermoplastic granulation, and other composite material forming processes. 1. Cannot be directly used in textile processing.
2. Textile-type sizing agents:
Core objective: To impart excellent textile processing properties to fiberglass filaments (such as flexibility, abrasion resistance, delamination, antistatic properties, and cohesion), enabling them to smoothly pass through textile processes such as warping, weaving, and knitting.
Key components: Starch or oil is the main film-forming agent and binder, supplemented with a large amount of lubricants (mineral oil, emulsified grease), softeners, antistatic agents, etc. Usually contains no or only a small amount of coupling agents.
Characteristics: The coated filaments (called "textile yarn") are soft, smooth, and have relatively weak cohesion. Mainly used in the production of various fiberglass fabrics (cloth, tape, sleeves, etc.), sewing threads, filter cloths, etc. The coating usually needs to be burned off (heat treatment) and reapplied with a reinforcing sizing agent (post-treatment) before the composite material is formed; otherwise, the interfacial bonding is very poor.
3. Reinforcing textile-type sizing agents:
Core objective: To balance the good textile processing properties of fiberglass filaments with their certain reinforcing interfacial properties in composite materials. This is a compromise between the first two types of sizing agents.
Key components: It contains a certain amount of coupling agent (but the proportion is usually lower than that of pure reinforcing agents), as well as film-forming agents that provide textile properties (such as modified starch or synthetic resin) and lubricants.
Characteristics: The properties of the precursor fiber are between those of reinforcing and textile types, possessing a certain degree of flexibility and weavability, while retaining a certain degree of compatibility with resins. It is mainly used to produce composite fabrics (such as some laminate base fabrics and needle-punched felt substrates) that do not have extremely high interfacial requirements and require certain textile processing steps. Some products can eliminate post-processing steps during composite molding, simplifying the process.
Summary
Sizing agents are far more than simple "lubricating coatings"; they are key materials throughout the entire life cycle of fiberglasss, from drawing and forming to post-processing and composite material applications. Their carefully designed complex multiphase structure endows fiberglass monofilaments with bundling capabilities, processing performance, and crucial interfacial bonding functions.
Precisely selecting and applying the appropriate type of sizing agent (reinforcing, textile, or reinforced textile) based on the intended use of the final product is a core process for ensuring excellent performance and high production efficiency of fiberglass and its end products. It perfectly illustrates the powerful role of surface chemistry in materials engineering.
