Time–Temperature Superposition of the Dissolution of Wool Yarns in the Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate

The dissolution of wool yarns in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim][OAc] has been investigated. Wool yarns were submerged into [C2mim][OAc] and dissolved for various times and temperatures before coagulating with water. Optical microscopy was used to track the yarn’s cross-sectional area. We propose that there are two competing dissolution processes, one rate-limited by disulfide bonds at low temperatures (LTs), and a second by hydrogen bonds at high temperatures (HTs), with a crossover point between the two regimes at 70 ℃. The corresponding activation energies were ELT = 127 ± 9 kJ/mol and EHT = 34 ± 1 kJ/mol. The remaining area of the dissolved wool yarn could be shifted via time–temperature superposition to plot a single master curve of area against time for both regions. Finally, the dissolution could be modelled by a diffusion process, giving self-diffusion coefficients for the [C2mim][OAc] ions (0.64–15.31 × 10−13 m2/s)

Effect of water on the dissolution of flax fiber bundles in the ionic liquid 1-ethyl-3-methylimidazolium acetate

This work investigated the dissolution rate of flax fibers in the ionic liquid 1-ethyl-3-methylimidazolium acetate [C2mim] [OAc] with the addition of a cellulose anti-solvent, water. The dissolution process was studied as a function of time, temperature and water concentration. Optical microscopy is used to analyse the resultant partially dissolved fibers. Distilled water was added to the solvent bath at the concentrations of 1%, 2% and 4% by weight in order to understand its influence on the dissolution process. The effect of the addition of even small amounts of water was found to significantly decrease the speed of dissolution, decreasing exponentially as a function of water concentration. The resulting data of both pure (as received from the manufacturers) ionic liquid and ionic liquid/anti-solvent mixtures showed the growth of the coagulated fraction as a function of both dissolution time and temperature followed time temperature superposition. An Arrhenius behavior was found, enabling the measurement of the activation energy for the dissolution of flax fiber. The activation energy of the IL as received (0.2% water) was found to be 64 ± 5 kJ/mol. For 1%, 2% and 4% water systems, the activation energies were found to be 74 ± 7 kJ/mol, 97 ± 3 kJ/mol and 116 ± 0.6 kJ/mol respectively. Extrapolating these results to zero water concentration gave a value for the hypothetical dry IL (0% water) of 58 ± 4 kJ/mol. The hypothetical dry ionic liquid is predicted to dissolve cellulose 23% faster than the IL as received (0.2% water)

Dissolution of hemp yarns by 1-ethyl-3-methylimidazolium acetate studied with time-temperature superposition

This study investigated the dissolution of hemp yarns in the ionic liquid 1-ethyl-3-methylimidazolium acetate. The yarns were submerged in the ionic liquid at various temperatures and times, then coagulated in water. This resulted in the formation of a composite yarn where two optical microscopy methods were employed to track the growth of the coagulated matrix. In the first, the submerged yarns within water were measured from a side view. In the second, the yarns were dried then analysed by encapsulating in epoxy resin. In both methods, the growth of the swollen ring thickness and the coagulated fraction was tracked as a function of time and temperature. It was found to obey time-temperature superposition, giving a dissolution activation energy of . In water the yarn is swollen; the swelling ratios of the different regions were calculated to be for the outer dissolved ring and the undissolved core, respectively. A novel finding in this study was that the growth of the coagulated region follows a diffusion process, increasing with the square root of time, and so could be modelled to give a diffusion coefficient for the ionic liquid of . This compared well with previously published NMR data for a saturated cellulose solution (23.5%). This strongly suggests that the diffusion of the ions through a saturated layer of cellulose solution controls the dissolution of the yarn. This finding has significant implications for cellulose-based composite production and thus the recycling of cellulose textiles

Design of experiments in the optimization of all-cellulose composites

In this work, statistical design of experiments (DoE) was applied to the optimization of all cellulose composites (ACCs) using cotton textile and interleaf films under applied heat and pressure. The effects of dissolution temperature, pressure and time on ACC mechanical properties were explored through a full factorial design (23) and later optimized using Response Surface Methodology. It was found that the experimental design was effective at revealing the underlying relationship between Young’s modulus and processing conditions, identifying optimum temperature and time settings of 101 °C and 96.8 min respectively, to yield a predicted Young’s modulus of 3.3 GPa. This was subsequently validated through the preparation of in-lab test samples which were found to exhibit a very similar Young’s modulus of 3.4 ± 0.2 GPa, confirming the adequacy of the predictive model. Additionally, the optimized samples had an average tensile strength and peel strength of 72 ± 2 MPa and 811 ± 160 N/m respectively, as well as a favorable density resulting from excellent consolidation within the material microstructure. This work highlights the potential of DoE for future ACC process understanding and optimization, helping to bring ACCs to the marketplace as feasible material alternatives

The influence of the hybridisation configuration on the mechancial properties of hybrid self reinforced polyamide 12/carbon fibre composites

This paper compares and contrasts the properties of self-reinforced polyamide 12/carbon fibre hybrid composites made by three different hybridisation routes, termed intra-yarn, intra-layer and inter-layer. The starting point for each route was to manufacture layers of woven cloth (containing both components), from which the hybrid composites were manufactured using the Leeds hot compaction technique. In all cases, a carbon fibre volume fraction of around 8% was the target. On balance, the intra-layer hybrids had the best combination of properties, although all three hybridisation routes yielded interesting results. This intra-layer hybrid configuration showed a significant increase in tensile modulus and strength, bending modulus and strength and penetration impact energy compared to a pure self-reinforced polyamide sheet. The only negative aspect was a reduction in the tensile failure strain from 11 to 2%, whereas the ductility in bending was unaffected by the incorporation of the carbon fibres

Dissolution of viscose rayon multifilament yarn in the ionic liquid 1-ethyl-3-methylimidazolium acetate studied using time–temperature superposition

Wide-angle X-ray diffraction (WAXS) and mechanical testing techniques are used to track the dissolution of a viscose rayon multifilament yarn in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim]+ [OAc]− for different times and temperatures. In the dissolution process, the oriented cellulose II crystals in the regenerated cellulose fibres dissolve and then reform into randomly oriented crystals to form a matrix phase, and this change in orientation enables us to follow the dissolution process using WAXS, and hence determine the dissolved matrix volume fraction vm . The change in the average molecular orientation P2 determined from an azimuthal (α ) X-ray scan, allows the growth of the matrix volume fraction vm to be calculated with time and temperature. The growth of vm was found to follow time temperature superposition, with an Arrhenius behaviour, giving a value for the activation energy of Ea = 149 ± 4 kJ/mol. Young’s modulus was measured on all the resulting processed composites. The fall of Young’s modulus with dissolution time and temperature was also found to follow time–temperature superposition, with an Arrhenius behaviour giving a value for Ea = 198 ± 29 kJ/mol. The Young’s Modulus results plotted against vm determined from the WAXS measurements fitted well to the Voigt upper bound parallel Rule of Mixtures

Analysis of fibre orientation distribution in short fibre reinforced polymers: a comparison between optical and tomographic methods

The fibre orientation distribution in a material sample of short fibre reinforced polyamide extracted from an injection moulded notched plate was analysed using two different methods, one based on micro-computed tomography and the Mean Intercept Length concept and the other based on the classical optical section method. The two methods were compared in terms of the preferred fibre orientation at a chosen position, and the agreement was found to be excellent provided the correct section plane was chosen for the optical method. The optical method was applied to different section planes to ascertain the best choice. Comparisons with the optical method, which can provide the full fibre orientation distribution, confirm that the analysis based on the MIL concept is capable of capturing important information about the fibre orientation

Hybrid carbon fibre/nylon 12 single polymer composites

This paper describes the production and properties of hybrid single polymer composites made from co-mingled tows of carbon and oriented nylon 12 fibres using the Leeds hot compaction process. For 22% volume fraction of carbon fibres, a well consolidated UD sample was made at a temperature of 176 °C, 2°C below the temperature at which major melting of the oriented PA12 fibres, and loss of molecular orientation, occurs. For braided cloth a higher temperature of 178°C was required to give a good sample, which is too close to the melting point of the PA12 multifilaments. Reducing the carbon fraction to 13% allowed a well consolidated sample (braided cloth) to be made at a lower temperature of 175°C, giving a wider temperature processing window. In tension the hybrid samples were found to fail in a brittle manner while in bending the behavior was ductile as long the molecular orientation was retained