Morphology and structure of constituent fibres in thermally bonded nonwovens

A new process has been developed to produce three-dimensional nonwovens directly from staple fibres. In order to establish suitable windows of the process parameters to achieve high-quality nonwoven products, the effects of thermal bonding temperature, dwell time and mould material on the morphology and structure of the fibre have been investigated using PP/PET bi-component fibres. It was evident from both scanning electron microscope images and Raman spectra that thermal-induced shrinkage of the PP sheath fibre occurred in the thermal bonding process, leading to deformation and cracking of the PP sheath and exposure of the PET core. X-ray diffraction results revealed crystal imperfection and/or less ordered polymer chains, more γ-form and thermal contraction of the crystal lattice for the PP sheath fibre, while birefringence measurements indicated that both the birefringence and the orientation factor for the PP fibre decreased after the thermal bonding process. The degrees of the thermal-induced shrinkage increased, and the crystallinity, birefringence and orientation factor of the PP sheath fibre decreased with increasing thermal bonding temperature, dwell time and thermal conductivity of the mould material. All these can be attributed to the different levels of modification of chemical composition caused by thermal oxidative degradation and thermalinduced relaxation of the orientation during the thermal bonding process. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.