An Efficient Composite Modifier Prepared for Enhancing the Crystallization and Flame-Retardancy of Poly(m-xylylene adipamide)

Poly(m-xylylene adipamide) (MXD6) has good gas barrier properties and high mechanical strength. However, in nature, this resin has a low rate of crystallization. In order to overcome this obstacle in its applications, this study prepares a new, efficient modifier for MXD6 by combining the synthesized DOPO derivative (DT) and P22. It is found that the use of the binary modifier exhibits obvious effects on the crystallization of MXD6. When 11.0 wt.% DT is added together with 0.1 wt.% P22 (DT/P22), the crystallization temperature of MXD6 shifts to a higher temperature of 19.7 °C, and the crystallinity degree of MXD6 is significantly increased by 60%. Meanwhile, this modifier exhibits obviously intumescent flame-retardancy on MXD6 by increasing the limited oxygen index (LOI) from 26.4% to 33.4%. The results of the cone calorimeter test (CCT) reveal that the peak heat release rate (PHRR), total heat release (THR) and average effective heat release (av-EHC) are obviously suppressed due to the use of this modifier. Moreover, the influences of this modifier on the crystal structures, mechanical and rheological properties of MXD6 are analyzed in detail. This study can provide an efficient modifier for MXD6.

The Effect of Stretching on the Crystal Structure and Crystal Orientation of PA510/SiO2 Films

In order to explore the relationship between the microstructure and macroscopic properties of PA510/SiO₂ films, the effect of the stretching on the crystal structure and crystal orientation of stretched PA510/SiO₂ films was studied. It could be seen from the transmission electron microscopy (TEM) graphs that the layered SiO₂ molecules were mainly oriented toward the machine direction (MD) and the dispersion could be improved by stretching. Through wide-angle X-ray scattering (WAXS) analysis, PA510/SiO₂ stretched films only contained a γ crystal form. During uniaxial stretching, especially for 1 × 3 film, the γ₁(100) crystal form was obviously oriented in the equatorial direction, and the orientation of γ₂(004) and γ₃(006) crystal forms could be observed in the meridian direction. According to the Herman orientation function, the orientation of the b-axis in the MD increased with the increase of the stretching ratio. It was worth noting that the orientation of the crystal region was more obvious. The addition of SiO₂ and the orientation of the crystalline and amorphous regions could improve the barrier properties of the films. The changes in the optical properties of stretched films were affected by the dispersion state of SiO₂ and the surface roughness.

Comparison of Crosslinking Efficiency in Dip and Roll-Deposited Coatings on Their Oxygen Barrier

Coating techniques are key factors in determining coated film properties. In the present study, nanocomposite coatings of poly(vinyl alcohol) and a nanoclay, montmorillonite, were deposited layer-by-layer using roll (doctor blade, DB) and dip coating techniques, in an effort to compare the impact of these techniques on the crosslinking efficiency and oxygen barrier of the coated films. The barrier properties at different relative humidities were tested, and the extent of nanoclay intercalation as well as the films' morphology was investigated. Barrier was further improved by crosslinking the coating with glyoxal and glutaraldehyde. Both techniques gave similar results but with a higher impact of relative humidity in roll coated films. Better results were achieved by tailoring the composition of those coatings to favor a higher density of hydrogen bonding in the coating.