Morphology-Mechanical Performance Relationship at the Micrometrical Level within Molded Polypropylene Obtained with Non-Symmetric Mold Temperature Conditioning

Abstract

The control of the structural properties of a polymeric material at the micro and nano-metrical scale is strategic to obtaining parts with high performance, durability and free from sudden failures. The characteristic skin-core morphology of injection molded samples is intimately linked to the complex shear flow, pressure and temperature evolutions experienced by the polymer chains during processing. An accurate analysis of this morphology can allow for the assessment of the quality and confidence of the process. Non-symmetric mold temperature conditions are imposed to produce complex morphologies in polypropylene parts. Morphological and micromechanical characterizations of the samples are used to quantify the effects of the processing conditions on the part performance. Asymmetric distribution of temperatures determines asymmetric distribution of both morphology and mechanical properties. The inhomogeneity degree depends on the time that one side of the cavity experiences high temperatures. The spherulites, which cover the thickest of the parts obtained with high temperatures at one cavity side, show smaller values of elastic modulus than the fibrils. When the polymer molecules experience high temperatures for long periods, the solid-diffusion and the partial melting and recrystallization phenomena determine a better structuring of the molecules with a parallel increase of the elastic modulus.

Extrusion and Injection Molding of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) (PHBHHx): Influence of Processing Conditions on Mechanical Properties and Microstructure

“…), with different semi-crystalline characteristics between the skin, shear, and core layers [65][66][67]. By increasing the mold temperature, the shear and skin layers reduce in thickness, providing more volume to the spherulitic core layer [68][69][70]. Morphological analysis on PHBHHx samples produced at mold temperatures M from 40 • C to 80 • C was performed in order to investigate the process-induced microstructure.…”

Intraspherulitic mechanical heterogeneities and microstructure of i-PP highlighted by nanoindentation and atomic force microscopy

“…Nanoindentation is most often used for the characterization of polymers considered homogeneous such as amorphous polymers like PMMA [22][23][24][25], PC [24,26], or PS [24]. For semi-crystalline polymers, nanoindentation was used on commercial samples prepared by conventional manufacturing processes, such as injection molding or extrusion, that usually induce a microstructure gradient between the skin and the core of the sample [27][28][29][30][31][32][33]. These studies aimed to evaluate the mechanical response in the different zones (skin-transition-core layers) of the prepared sample.…”