Guangdou Ye

Smart polymer fibers with shape memory effect

In this study, a series of smart polymer fibers with a shape memory effect were developed. Firstly, a set of shape memory polyurethanes with varying hard-segment content were synthesized. Then, the solutions of the shape memory polyurethanes were spun into fibers through wet spinning. The thin films of the polyurethanes were considered to represent the nature of the polyurethanes. Differential scanning calorimetry tests were performed on both the thin films and the fibers to compare their thermal properties. Wide angle x-ray diffraction and small angle x-ray scattering techniques were applied to investigate the structure of the thin films and the fibers, and the structure change taking place in the spinning process was therefore revealed. The spinning process resulted in the polyurethane molecules being partially oriented in the direction of the fiber axis. The molecular orientation prompted the aggregation of the hard segments and the formation of hard-segment microdomains. The mechanical properties of the fibers were examined through tensile tests. The shape memory effect of the thin films and the fibers was investigated through a series of thermomechanical cyclic tensile tests. It was found that the fibers showed less shape fixity but more shape recovery compared with the thin films. Further investigations revealed that the recovery stress of the fibers was higher than that of the thin films. The smart fibers may exert the recovery force of shape memory polymers to an extreme extent in the direction of the fiber axis and therefore provide a possibility for producing high-performance actuators.

Hydrogen bond and crystalline structure of the junction network in polyvinyl alcohol/dimethysulfoxide gels

The hydrogen bond and aggregation structures of polyvinyl alcohol (PVA) gels prepared with dimethylsulfoxide (DMSO) were investigated as were the the rheological properties. The variable temperature Fourier Transform Infrared (FTIR) and X-ray results of PVA-DMSO gels show that the hydrogen bond and crystalline structure are destroyed as temperature increases. In the Tanaka model, the value of ζ (the number of sequential units per chain in the junction) is 1.45 and s (the number of polymer chains in a single junction), which reveals the ability of solution to form gel, varied as a function of gel melting temperature Tgm. The results of dynamic rheology show that the elastic modulus G′ is proportional to the gel concentration and inversely proportional to the temperature. It was found that gels formed from solutions with same viscosities showed different properties. This is because a gel with a higher polymerization degree has a lower value of s.

Study of synthesizing energy storage microcapsules in PVA spinning solution and thermal regulating fibers prepared by this solution

Thermal regulating fiber has been a research hotspot worldwide recently. In this paper, the energy storage microcapsules composed of silicon dioxide (SiO2) as shell and paraffin as core were synthesized in the spinning solution of polyvinyl alcohol (PVA). This solution was used to prepare thermal regulating PVA fibers by wet spinning directly. Orthogonal experiment was conducted to optimize the synthetic conditions of the microcapsules. Chemical structure and morphology of the fibers were characterized by Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and scanning electron microscope (SEM) respectively. The thermal properties of the fibers were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Results present that energy storage microcapsules are successfully synthesized in PVA spinning solution with a mean particle size of 1.39 µm. The fibers containing such microcapsules show a high latent heat storage density of 45.39 J g−1, which also achieve a relatively better thermal stability.

Rheological Behavior of Blends of Poly(Phenylene Sulfide) with a Thermotropic Liquid Crystalline Aromatic Poly(Ether Ester)

A new type of thermotropic liquid crystalline aromatic poly(ether ester) (PEE) was prepared from 1,3-bis(4′-carboxyphenoxy)benzene, 1,4-diacetoxybenzene, and p-acetoxybenzoic acid through a melt transesterification process. The rheological behavior of blends of poly(phenylene sulfide) (PPS) with PEE was studied using a high-pressure capillary rheometer with the shear rate range of 50 s−1 to 3000 s−1. The results show that according to the range of shear rate, the flow curves of PEE/PPS blends can be divided into three zones: a first shear-thinning zone (n < 1, “n” represents non-Newtonian indexes), a shear-thickening zone (n > 1), and a second shear-thinning zone (n < 1), and the former two zones are more obvious with the increase of PEE content or elevated temperature. In the second shear-thinning zone, the PPS melt is close to a Newtonian fluid at high temperature and high shear rate; meanwhile the non-Newtonian behavior of the PPS melt at high temperature is enhanced with the addition of PEE. The apparent viscosity of PPS melts sharply dropped after adding PEE, especially at relatively low temperature and low shear rate. The curve of apparent viscosity vs. shear rate starts to flatten out after adding PEE, suggesting that the addition of PEE lowers the sensitivity of PPS to shear rate. As the content of PEE increases, the activation energy of the viscous flow, ΔEη, of PPS decreases, which means that adding PEE weakens the temperature sensitivity of the apparent viscosity of the PPS melt. It can clearly be seen that the addition of PEE is beneficial to the processing of PPS.

Influences of solution state on the formation of polyvinyl alcohol as-spun fiber during dry-wet gel spinning

The polyvinyl alcohol (PVA) as-spun fibers were prepared by dry-wet gel spinning, with dimethylsulfoxide (DMSO) as solvent and methanol as the cooling medium. The rheological properties of spinning solutions, matter exchanges, sonic orientation factor and entanglement of PVA as-spun fibers were investigated. Solution with lower PVA content at lower temperature has a same viscosity with the more concentrated solution at higher temperature. Solution with lower concentration has a higher G′ and a lower Tan δ, which leads to a lower sonic orientation factor for the fiber. The calculating results from the optical microscope show that solution with lower PVA content loses less DMSO due to the weaker gel ability and the possible phase separation during the coagulation. Moreover, solution more closed to the gel point bounds more DMSO, which makes the DMSO exchange difficult to process. The entanglement in the as-spun fiber decreases with the decreasing PVA content in the solution. Suitable crystallization and entanglement can obtain fibers with higher strength.