Did you know that fiberglass is the key ingredient in creating the steel frame of engineering plastics?
Engineering plastics are high-strength plastics used in industrial applications, characterized by high strength, high rigidity, dimensional stability, and creep resistance. These properties of engineering plastics stem not only from the properties of the plastic resin but also, and perhaps more importantly, from the fiberglass component incorporated into the plastic. Glass fiber acts as the "steel and framework" of engineering plastics, analogous to the reinforcing steel in concrete. Typically, alkali-free glass fiber is used in plastic production, and it comes in long, short, and flat forms. These different forms of glass fiber exhibit different properties.
Glass fiber, commonly found in the modified plastics industry, can be classified according to its composition and form:
Classified by chemical composition
Alkali-free fiberglass (E fiberglass): Alkali content <1%, balanced insulation, strength, and water resistance, highest production volume; used in wind turbine blades, PCBs, and plastic modification.
Medium-alkali fiberglass (C fiberglass): Alkali content 6%-12%, good acid resistance, weaker insulation, low cost; used in chemical corrosion protection and asphalt waterproofing.
Classification by morphology
Continuous untwisted long glass fiber: Glass fibers drawn into bundles and wound into rolls for use in textile processing and structural reinforcement;
Chopped glass fiber: Glass fiber rolls that are chopped after surface treatment; a major type of fiber used for plastic modification and reinforcement;
Flat glass fiber: A special type of glass fiber with an elliptical cross-section controlled during the drawing process; available in both long and chopped forms. It exhibits unique performance characteristics in applications.
How does fiberglass create the "steel and iron skeleton" of plastic?
The core reason why glass fiber is the perfect partner for engineering plastics lies in its ability to compensate for the performance shortcomings of pure plastic resins through a synergistic "fiber-resin" effect and cohesive force transfer.
Mechanical Strengthening: Like adding "steel bars" to plastics, tensile strength can be increased by 20% to 100%, and impact toughness can even approach the level of metals;
Deformation Resistance: It inhibits resin shrinkage, making products less prone to warping under high temperatures and stress, with shrinkage rates controlled to a minimum of 0.15%;
Cost Balancing: Compared to pure engineering plastics, fiber-reinforced materials can achieve high performance requirements at a lower cost. For example, replacing metal with long glass fiber PA in automotive parts reduces weight by 50% while lowering costs by 30%.
What are the unique properties of different types of glass fiber in plastics?
However, different forms of glass fiber bring vastly different effects to plastics. Choosing the right type can double the product's performance; choosing the wrong type may result in problems such as exposed glass fibers and easy breakage. Commonly used glass fibers mainly include long glass fibers, short glass fibers, and flat glass fibers, which differ significantly in morphology, performance, processing methods, and application scenarios.
Long glass fibers act like "solid steel bars," forming a continuous network within the resin, efficiently transferring stress. This is why their impact strength is 50% to 100% higher than that of short glass fibers.
Short glass fibers act like "crushed stone," uniformly dispersed but with limited length, suitable for applications requiring high isotropy.
Flat glass fibers, on the other hand, act like "thin steel sheets," with a thickness of 3 to 10 μm and a width of 50 to 200 μm. This allows for a contact area with the resin that is 3 to 5 times larger than that of round glass fibers, directly improving surface smoothness by one level.
Appearance Characteristics
① Flat Glass Fiber Filled PC
Due to its flat, ribbon-like structure, the contact area with PC resin is 3-5 times larger than that of round glass fiber of the same weight, resulting in a smoother transition between the fiber and resin interface. Combined with the low surface roughness achieved through a special drawing process, the surface gloss of the finished product (measured at a 60° angle) is high.
② Short Glass Fiber Filled PC
The short and uniformly dispersed fibers result in gentler light scattering. However, slight reflections still exist at the interface between the round cross-section fiber and resin, leading to a slightly lower gloss level than flat glass fiber, typically between 70 and 80. The floating fiber effect places higher demands on the molding process.
③ Long Glass Fiber Filled PC
Long fibers (6-12mm) are prone to localized aggregation during processing, and the fiber-resin interface has tiny gaps due to the "skeleton effect." Light undergoes diffuse reflection in these areas, resulting in a gloss level of only 50-60, with a slightly matte surface. This is more suitable for functional products such as engineering machinery housings.
Mechanical Properties
The longer the glass fiber in a plastic, the more bonding points between the glass fiber and the resin, resulting in better strength.
Long glass fiber plastics can be considered the undisputed "strength champions." Data shows that, for the same content, the tensile strength of long glass fiber reinforced PA is 20%~30% higher than that of short glass fiber, and the notched impact strength is 50%~60% higher, making it particularly suitable for components subjected to long-term stress, such as automotive bumpers and motor fan blades.
Short glass fiber excels in "balance." Although its strength is slightly lower, it has good isotropy, with minimal performance differences in all directions, making it suitable for precision parts such as gears and connectors.
Flat glass fiber, on the other hand, slightly improves "lateral toughness." Using flat glass fiber reinforced silicone copolymer PC in mobile phone casings improves drop resistance by 40% and avoids the defect of "exposed glass fiber."
Dimensional Stability
Long glass fibers exhibit a strong "skeleton effect" that effectively holds the resin in place, resulting in shrinkage as low as 0.15% in the flow direction. However, they show significant differences in shrinkage in the vertical direction, making large-area flat panels prone to warping.
Short glass fibers shrink more uniformly, making them suitable for small to medium-sized parts.
Flat glass fibers, with their flat structure, offer more balanced control over in-plane shrinkage, making them an ideal choice for automotive interior panels.
