Influence of reprocessing on the mechanical properties and structure of polyamide 6

In this study, virgin polyamide 6 (PA6) was repetitively processed via a conventional processing procedure until the 16 processing cycle was completed. Virgin and reprocessed PA6 coming from each cycle were characterized to evaluate mechanical and theological properties to be correlated with the number of processing cycles. Changes in chemical structure, molecular weight, molecular weight distribution, and crystalline behavior were also analyzed after each cycle. Gel permeation chromatography (GPC) results showed that a reduction in the molecular weight and an increase in the molecular weight distribution as a consequence of a decrement in melt viscosity of PA6, but the chemical structure of the PA6 remained unchanged in the FTIR spectra. DSC thermal analysis revealed that crystallization rate was increased with increasing reprocessing cycles, and the crystallite size distribution was changed as a consequence of chain scission during reprocessing. The mechanical properties showed that there is an increment in tensile yield stress, flexural strength and modulus after each reprocessing cycle, whereas a decrement in Izod impact strength. (C) 2007 Elsevier B.V. All rights reserved.