高压下尼龙6的拉曼光谱研究

e-Polymers2011, no. 049

ISSN 1618-7229

A Raman study of nylon 6 annealed under high pressure Weijie Xu , Dahu Cao,*Qiang Yu

*School of Materials Science & Engineering, Changzhou University, Changzhou, China; fax: 86-0519-********; e-mail: caodh2003@.

(Received: 02 July, 2010; published: 17 May, 2011)

Abstract:Using a cubic-anvil high pressure apparatus, nylon 6 samples were

annealed under 400 MPa to 1.5 GPa. The structure changes of nylon 6 are

studied by the methods of wide-angle X-ray diffraction (WAXD), differential

scanning calorimetry (DSC) and Raman spectra. Compared with sample prepared

at ambient pressure, high pressure treatment makes the hydrogen-bonded sheets

pack more closely and thus enhanced CH2vibration out of the hydrogen-bonded

sheets. After high pressure treatment, it is observed that all changes of C-C related

vibration modes in nylon 6 are similar with ones in nylon series when the CH2

sequence number increased, from which it is deduced that high pressure treatment

reduces the effects of amide group on the chain conformation of nylon 6.

Introduction

High pressure treatment often causes drastic structure, morphology and physical property changes in polymers. Studies have shown that polyethylene would convert into hexagonal phase from orthorhombic structure at moderately high temperature and above 350MPa [1]. A different kind of polymer morphology, called extended-chain crystals [2-5], can be formed under high pressure instead of spherulites crystals obtained at ambient pressure.

So far, most of the high pressure researches on polymer treatment are focused on the preparation of different kinds of extended-chain crystals [6-8] and their formation mechanism [9-12] motivated by the excellent strength of extended-chain crystals predicted in theory. It is reasonable to deduce from researches on proteins [13],which also have long chain conformation, that high pressure should have more subtle effects on the polymers, such as structure changes of groups, conformation and intermolecular interaction, however, these effects were not studied extensively except for polyethylene [14,15].

Nylon 6, widely used as an important engineering plastic, like other polymers [6-8] forming extended-chain crystals under high pressure [16,17], has linear molecular structure composed of symmetrical molecular backbones, whose vibration bands often show strong peaks in Raman spectra [18-19], a powerful test method to analyze the changes of the polymer skeleton [20].

The first synthesis of nylon 6 extended-chain crystals and its FTIR spectra study were reported by Gogolewski et al. [21] in 1973. So far, the effects of pressure on the melting point and crystallinity in nylon 6 had been studied by a few researchers [16,17, 21], and there is no Raman spectra study on high pressure treated nylon 6.

The present paper describes in detail the microstructure changes of nylon 6 annealed under high pressure with Raman spectra and other methods. The results show that