Weldline integrity of reinforced plastics: Effect of filler shape

Abstract

The paper is a preliminary report on glass fiber and glass flake orientation in the weldline zone of injection molded reinforced polypropylene. Two types of weldlines were studied using simple shape molds: one where two melt streams meet head‐on and become immobilized, the other where the weldline formation is followed by additional flow. In the weldlines of the first type, which are characteristic of current standard molds used to test weldline strength, the anisometric particles are almost perfectly oriented perpendicular to flow. As a result, the weldlines of this type tend to be weak and brittle. In the second case when the weldline is formed by merging of melt streams separated by an insert, particle orientation in the weldline area remains different from other areas of the sample for long distances from the insert. It is shown that in molds where the weldline formation is followed by laterally expanding flow the change of particle orientation is faster than for unidirectional flow.

Application of Statistic Estimation to Weldline Strength of Injectionmolded Thermoplastic Composites

“…This result matches with the data published by other researchers using different composite materials (PP [9][10][11][12][13], Noryl [12], PS, PBT, PET [13]). The weakness of Application of Statistic Estimation to Weldline Strength of Composites the weld area is mainly attributed to the lack of fiber flow across the weldline, which makes the material in the weldline region act as if it is not reinforced.…”

Polymer micro and nanocomposites: Structure, interactions, properties

“…Fountain flow in the mold leads to the orientation of particles parallel with the melt front resulting in decreased weld line strength [118,119]. The phenomenon is demonstrated by Fig.…”

Particulate Fillers in Thermoplastics

“…The orientation of anisotropic filler particles has an especially pronounced effect on the strength of injection molded parts containing weld lines. Fountain flow in the mold leads to the orientation of particles parallel with the melt front resulting in decreased weld line strength [164][165][166]. Increasing particle size and filler content result in a decrease of the weld line strength [164,167], which can be improved by changing particle characteristics (size, treatment, aspect ratio) [164] and mold construction [165].…”