Regrind Fractions Nobody Writes into the Grade Specification
Undeclared regrind degrades melt stability and impact strength; verify batch history using melt flow rate delta and oxidative induction time limits.
Critical Fiber Length
Meaning
Mechanical threshold defines the minimum fiber size needed to effectively reinforce a polymer matrix. Stress moves from the plastic resin to the fiber through the interface between the two materials. The value is specific to the fiber-resin pairing and does not predict the behavior of unreinforced materials.
Load Transfer
Surface area must be large enough to support the applied load without the fiber pulling out of the plastic. For a composite to gain strength, the fiber must be longer than the critical fiber length to ensure efficient stress distribution. Short fibers often pull out of the matrix before they can contribute to the overall tensile strength.
Reinforcement Efficiency
Maximum reinforcement occurs when the majority of the fibers exceed this physical limit. If the processing method breaks the glass or carbon below the critical fiber length, the resulting part will be brittle and weak. Impact resistance also depends on the ability of the fiber to bridge cracks.
Structural Performance
Moulding conditions like high back pressure and fast injection speeds can reduce the average length of the reinforcement. Engineers measure the critical fiber length to determine the theoretical limit of a material’s performance. Chemical coupling agents improve the bond between the resin and the fiber.