NMR Investigations of Orientational and Structural Changes in Polyamide-6 Yarns by Drawing

Disassociated molecular orientation distributions of a composite cellulose-lignin carbon fiber precursor: A study by rotor synchronized NMR spectroscopy and X-ray scattering

Cellulose-lignin composite carbon fibers have shown to be a potential environmentally benign alternative to the traditional polyacrylonitrile precursor. With the associated cost reduction, cellulose-lignin carbon fibers are an attractive light-weight material for, e.g. wind power and automobile manufacturing. The carbon fiber tenacity, tensile modulus and creep resistance is in part determined by the carbon content and the molecular orientation distribution of the precursor. This work disassociates the molecular orientation of different components in cellulose-lignin composite fibers using rotor-synchronized solid-state nuclear magnetic resonance spectroscopy and X-ray scattering. Our results show that lignin is completely disordered, in a mechanically stretched cellulose-lignin composite fiber, while the cellulose is ordered. In contrast, the native spruce wood raw material displays both oriented lignin and cellulose. The current processes for fabricating a cellulose-lignin composite fiber cannot regain the oriented lignin as observed from the native wood.

Determination of molecular orientation of uniaxially stretched polyamide fibers by polarized infrared spectroscopy: comparison of X-ray diffraction and birefringence methods

Polarized infrared (IR) spectroscopy has been used to determine the crystalline and amorphous orientation of polyamide fibers. The transition moment angle of the band at 936 cm-1 of PA66 was determined to be 48 degrees using IR spectroscopy and birefringence measurement. The crystalline orientation of PA66 fibers was estimated from the band at 936 cm-1 while the amorphous orientation of PA66 fibers was obtained by an indirect method. The alpha crystalline orientation of PA6 has been obtained using the band at 930 cm-1 and the amorphous orientation of PA6 has been determined using the band at 1124 cm-1. Crystalline orientation increased rapidly at low draw ratios (DR<3) and increased slowly at higher draw ratios (DR>3) for both PA66 and PA6 fibers, while the amorphous orientation increased slowly throughout the whole extension range for PA66 fibers. A good correlation was found between the crystalline orientation values obtained by infrared spectroscopy and other methods such as X-ray diffraction for PA66 and PA6 fibers. On the basis of this observation, it has been concluded that polarized infrared spectroscopy can be used reliably to measure the orientation of polyamide fibers without combining with other techniques.

Measurement of orientation distributions using chemical shift amplification

A new three-dimensional magic angle spinning (MAS) experiment is proposed, based on a combination of the two-dimensional rotor-synchronized MAS experiment of Spiess and co-workers and a new chemical shift anisotropy amplification method. The new experiment is demonstrated on a macroscopically ordered sample of ultra-high molecular weight poly(ethylene).