Mechanical Analysis of Woven Fabrics:The State of the Art

The automation and integration of processes in the textile industry is dictated by the increasing need to offer specialized products at optimum quality and low cost, satisfying at the same time the fast cycles of fashion trends or in the case of technical applications the delivery of products of high qualiy and of exact properties. Under these premises, computer engineering tools, such as computer-aided engineering (CAE) and computer-aided design (CAD), have recently gained attention. The revolutionary role of CAE and CAD tools in the textile industry is the guaranty that the final product meets the set specifications, optimizing thus the quality control procedure. Moreover, the prediction of the properties and the aesthetic features of the product before the actual fabrication can essentially benefit the textile research community [Hu and Teng, 1996]. Especially nowadays that textile materials can be used for the production of a wide range of technical products, such as reinforcements in composites for aerospace or marine applications or textiles for medical applications, the prediction of the end-product’s mechanical properties is of major importance. Furthermore, the textile raw materials are processed under low-stress conditions and it is thus reasonable to assume that the knowledge of the possible modifications introduced via the manufacturing process is necessary for the final product realization (Hu, 2004). Textiles are flexible, anisotropic, inhomogeneous, porous materials with distinct viscoelastic properties. These unique characteristics makes textile structures to behave essentially different compared with other engineering materials. Moreover, textiles are characterized by an increased structural complexity. Their properties mainly depend on a complicated combination of their structural units and their interactions. The complicated nature of the textiles’ mechanics makes them ideal candidates for a mechanical analysis using computerbased methods

Characterisation of the supramolecular structure of chemically and physically modified regenerated cellulosic fibres by means of high-resolution Carbon-13 solid-state NMR

Carbon-13 high-resolution solid-state NMR techniques have been invaluable in elucidating the structure of regenerated cellulosic materials. Studies of a range of fibres have shown systematic changes in chemical shifts, which can be related to the influences of physical processing or chemical modification. A constrained curve fitting method has been applied, where the C4 spectral envelope is represented as the sum of contributions from polymer in ordered, partially-ordered and disordered environments, associated with differing conformational arrangements of the cellulose hydroxymethyl and glycocidic bonds. The empirical gamma-gauche effect seems likely to provide the best rationalization for the relationship between C4 shifts and conformational order, taking into account the increased range of bond angles in disordered environments. The quantification of proportions of polymer units within different conformational groupings will provide new insights into the development of supramolecular texture. This will allow better appreciation of the relationships between fibre processing and ultimate fibre performance

The hydrolysis and recrystallisation of lyocell and comparative cellulosic fibres in solutions of mineral acid

Regenerated cellulosic fibres undergo a process described as scission-reordering during hydrolysis in solutions of mineral acid. This occurs within disordered polymer regions at lateral crystal interfaces, which are accessible to aqueous agents through the pore spaces and polymer free volume. This process is distinct from that of oligomer-solubilsation, which occurs within disordered polymer regions in series between crystal domains, where no effective template exists for recrystallisation. The degradation of series disorder will have the greatest influence on fibre tensile properties, which fall dramatically even at low levels of hydrolysis. The mechanics of fibrillation are most sensitive to the degradation of lateral disorder, which occurs at a higher rate constant. Soft-touch fabric processing may therefore be possible under conditions where there is a reduced influence on tensile performance. A kinetic model has been proposed to describe the hydrolysis and recrystallisation pathways, which shows that lyocell has longer but thinner crystal domains than viscose or modal fibres, and also a tighter distribution of lateral crystal sizes. Lyocell also has a lower proportion of series disorder and also thinner regions of lateral disorder. This is consistent with the overall greater crystallinity of the original lyocell fibre and the also of the final microscrystalline product

Carbon-13 solid state NMR investigation and modeling of the morphological reorganization in regenerated cellulose fibres induced by controlled acid hydrolysis

CPMAS carbon-13 NMR has been used to follow structural changes affecting regenerated cellulose fibres during hydrolysis by mineral acids. The C4 envelope of regenerated cellulose was deconvoluted into separate peaks, for ordered (crystal), part-ordered (surface) and disordered (non-crystal) polymer, which allowed calculation of average crystal lateral sizes, in good agreement with WAXD data. A geometrical model has been used to describe recrystallisation at lateral crystal faces, occurring within a disordered boundary surrounding the crystal interior. A one-dimensional relaxation-diffusion model has also been constructed, appropriate to the spinodal structure of lyocell. This has provided estimates of proton T1ρ relaxation times for pure crystalline (cellulose II) and non-crystalline cellulose, around 24 and 4.5 ms, respectively, at a 45 kHz B1 field. From the model, crystalline and non-crystalline regions in lyocell are estimated to each be around 2.5 nm thickness for a material of 50% crystallinity, consistent with the 2–3 nm dimensions derived from C4 peak devonvolution