The reinforcement of polyamides with nanometric layered silicates represents nowadays an innovative strategy to produce high performance plastics with enhanced structural and functional properties. Even if the presence of very low silicate content, usually less than 5 wt %, allows polymer nanocomposites to be produced with conventional processing equipment, the difficulty in conveniently tuning materials and processing parameters, to control the developed nanomorphology, presents a great limit for applications on an industrial scale. Therefore, the study of the processability of polyamide based nanocomposites is crucial in order to control, predict and optimize their final properties. In particular, a better understanding of the effects of elongational flow on final nanostructure is fundamental in the cases of film or fibre extrusion in which elongational flow is very common. The aim of this work is to investigate the effects of elongational flow on clay dispersion, exfoliation, orientation and crystallinity of polyamide based nanocomposites. Hybrids with different loadings of a commercial organoclay were produced by melt compounding using two polyamide matrices: a nylon 6 and a copolyamide, with similar molecular weight. The elongational flow characterization was performed both in non-isothermal and isothermal conditions by using, respectively, fibre spinning technique and an elongational rheometer (SER). During the spinning tests, fibres of neat matrices and hybrids were collected at different draw ratios and submitted to morphological characterization by TEM, small angle X-Ray (SAXD), DSC, and wide angle X-ray (WAXD) analyses. The properties of copolyamide based nanocomposites were compared to nylon 6 ones in order to examine the effect of polymer molecular structure on the structural modifications upon drawing as well as to establish the relationship between processing, nanomorphology and properties. Finally, the Halpin-Tsai method was applied to calculate the modulus of the nanocomposite fibres at different draw ratios, as a function of various parameters, including the exfoliation ratio, clay layer and cluster aspect ratios. Since all hybrids studied in this work were characterized by intercalated/exfoliated morphology, the calculation, using the Halpin-Tsai method, was divided into two stages. Young’s modulus for the exfoliated region was computed first by considering this region as a two-phase system: the neat matrix and the exfoliated clay platelets. The exfoliated region with the computed Young’s modulus was then considered as the effective matrix phase in the second stage of calculation, in which the intercalated region was the inclusion phase.

Effect of extensional flow on morphology and properties of polyamide layered silicate nanocomposites

GAROFALO, EMILIA
2008-01-01

Abstract

The reinforcement of polyamides with nanometric layered silicates represents nowadays an innovative strategy to produce high performance plastics with enhanced structural and functional properties. Even if the presence of very low silicate content, usually less than 5 wt %, allows polymer nanocomposites to be produced with conventional processing equipment, the difficulty in conveniently tuning materials and processing parameters, to control the developed nanomorphology, presents a great limit for applications on an industrial scale. Therefore, the study of the processability of polyamide based nanocomposites is crucial in order to control, predict and optimize their final properties. In particular, a better understanding of the effects of elongational flow on final nanostructure is fundamental in the cases of film or fibre extrusion in which elongational flow is very common. The aim of this work is to investigate the effects of elongational flow on clay dispersion, exfoliation, orientation and crystallinity of polyamide based nanocomposites. Hybrids with different loadings of a commercial organoclay were produced by melt compounding using two polyamide matrices: a nylon 6 and a copolyamide, with similar molecular weight. The elongational flow characterization was performed both in non-isothermal and isothermal conditions by using, respectively, fibre spinning technique and an elongational rheometer (SER). During the spinning tests, fibres of neat matrices and hybrids were collected at different draw ratios and submitted to morphological characterization by TEM, small angle X-Ray (SAXD), DSC, and wide angle X-ray (WAXD) analyses. The properties of copolyamide based nanocomposites were compared to nylon 6 ones in order to examine the effect of polymer molecular structure on the structural modifications upon drawing as well as to establish the relationship between processing, nanomorphology and properties. Finally, the Halpin-Tsai method was applied to calculate the modulus of the nanocomposite fibres at different draw ratios, as a function of various parameters, including the exfoliation ratio, clay layer and cluster aspect ratios. Since all hybrids studied in this work were characterized by intercalated/exfoliated morphology, the calculation, using the Halpin-Tsai method, was divided into two stages. Young’s modulus for the exfoliated region was computed first by considering this region as a two-phase system: the neat matrix and the exfoliated clay platelets. The exfoliated region with the computed Young’s modulus was then considered as the effective matrix phase in the second stage of calculation, in which the intercalated region was the inclusion phase.
2008
9788878970205
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/3018832
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