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.
Highlights
Received: 31 December 2020The knowledge of the structural properties of a polymeric material on the micro and nanometric scale is strategic to obtain parts with high performance, durable and free from sudden failures [1,2]
Nano-indentation is a recently developed technique, which differs from traditional hardness tests in the possibility of monitoring the depth of penetration during the loading and unloading phases [10,11,12]
The findings suggest that both morphology and mechanical properties depend on the temperature and flow fields during the injection molding process [25]
Summary
Received: 31 December 2020The knowledge of the structural properties of a polymeric material on the micro and nanometric scale is strategic to obtain parts with high performance, durable and free from sudden failures [1,2]. Determining the mechanical properties of the individual phases with traditional techniques is challenging due to the size of the structures [5]. For this reason, micro and nanoscale characterization techniques have established themselves both in the field of scientific research and in the field of industrial research [6]. Nano-indentation is a recently developed technique, which differs from traditional hardness tests in the possibility of monitoring the depth of penetration during the loading and unloading phases [10,11,12]. HarmoniX and peak force AFM techniques are able to simultaneously provide topographic and mechanical maps during the scanning of the sample at the nanometric scale [14,15,16].
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