Miscibility and isothermal crystallization behavior of polyamide 6/poly(vinyl alcohol) blend

Investigation of Transport Mechanism and Nanostructure of Nylon-6,6/PVA Blend Polymers

A casting technique was used to prepare poly(vinyl alcohol) (PVA) blend polymers with different concentrations of Nylon-6,6 to increase the free-volume size and control the ionic conductivity of the blended polymers. The thermal activation energy for some blends is lower than that of pure polymers, indicating that their thermal stability is somewhere in between that of pure Nylon-6,6 and pure PVA. The degree of crystallinity of the blend sample (25.7%) was lower than that of the pure components (41.0 and 31.6% for pure Nylon-6,6 and PVA, respectively). The dielectric properties of the blended samples were investigated for different frequencies (50 Hz-5 MHz). The σ_ac versus frequency was found to obey Jonscher's universal power law. The calculated values of the s parameter were increased from 0.53 to 0.783 for 0 and 100 wt.% Nylon-6,6, respectively, and values less than 1 indicate the hopping conduction mechanism. The barrier height (Wm) was found to increase from 0.33 to 0.72 for 0 and 100 wt.% Nylon-6,6, respectively. The ionic conductivity decreases as the concentration of Nylon-6,6 is blended into PVA because increasing the Nylon-6,6 concentration reduces the number of mobile charge carriers. Positron annihilation lifetime (PAL) spectroscopy was used to investigate the free volume's nanostructure. The hole volume size grows exponentially with the concentration of Nylon-6,6 mixed with PVA. The Nylon-6,6/PVA blends' free-volume distribution indicates that there is no phase separation in the blended samples. Mixing PVA and Nylon-6,6 resulted in a negative deviation (miscible blends), as evidenced by the interaction parameter's negative value. The strong correlation between the free-volume size and other macroscopic properties like ionic conductivity suggests that the free-volume size influences these macroscopic properties.

Effect of silver nitrate on the thermal processability of poly(vinyl alcohol) modified by water

The thermal processing of poly(vinyl alcohol) (PVA) is a big challenge worldwide. In this article, silver nitrate (AgNO3), which can combine with the hydroxyl groups of PVA and water, was introduced to further improve the thermal processability of the poly(vinyl alcohol)/water system. The water states, thermal performance, and rheological properties of PVA modified by AgNO3 were investigated. The results showed that with the increasing of AgNO3 content, the content of bound water in system increased ascribing to the interaction among PVA, water and AgNO3, indicating that the bondage of PVA matrix on water enhanced, thus retarding the tempestuous evaporation of water in system during melt process and making more water remain in system to play the role of plasticizer. Meanwhile, that AgNO3 combined with the hydroxyl groups of PVA further weakened the self-hydrogen bonding of PVA, guaranteeing a lower melting point and higher decomposition temperature, and broadening the thermal processing window. The rheological properties of the modified PVA system showed that the torque and die pressure of the modified PVA system turned to stabilization during melt processing, testifying that the thermal processability of the PVA/water system was largely improved.

New insight into non-isothermal crystallization of PVA-graphene composites

The melt crystallization of poly(vinyl alcohol) (PVA) and PVA composites has been a controversial subject due to inconclusive evidence and different opinions for its decomposition during crystallization. Using graphene as a model, the melt crystallization of PVA and PVA-graphene composites occurring during single-cycle and multiple-cycle non-isothermal annealing processes was systematically analyzed using different characterization techniques. The results obtained using single-cycle non-isothermal annealing indicated that the entire crystallization process took place through two main stages. The graphene in the PVA matrix regulates the nucleation and crystal growth manner of the PVA, yet resulting in retardation of the entire crystallization. The FTIR and Raman spectroscopic results particularly demonstrated that the annealing process not only improved the crystallinity but also led to clear decomposition in PVA and PVA-graphene composites, such as the elimination of hydroxyl groups and the production of C=C double bonds. The newly produced C=C double bonds were found to be responsible for the retardation of PVA macromolecule crystallization and the breaking of hydrogen bonds among the hydroxyl groups in the PVA chains. In addition, the morphological observation and multi-cycle non-isothermal crystallization further confirmed the existence of decomposition based on the surface damage as well as decreased crystallization enthalpy and crystallization peak temperature. Therefore, the non-isothermal crystallizations of the pure PVA and the PVA-graphene composites were in fact the combination of non-isothermal crystallization and non-isothermal degradation processes.

High impact toughness of polyamide 6/poly (vinylidene fluoride) blends induced by an ionic liquid

This study reports the high impact toughness of polyamide 6 (PA6)/poly (vinylidene fluoride) (PVDF) blends achieved via adding an ionic liquid. The presence of the ionic liquid in the blends promotes the transformation of sea-island structure into co-continuous morphology, which to a large extent accounts for the improvement in toughness. In addition, it is believed that the enhanced mobility of the PA6 matrix by the ionic liquid also contributes to the high impact toughness.