Ajit Ranade

Exfoliated and intercalated polyamide-imide nanocomposites with montmorillonite

Abstract Polyamide-imide (PAI) is a high performance condensation polymer, which has high heat resistance and high radiation resistance. Solvent suspensions of PAI are widely used in magnetic wire coatings. Montmorillonite (MMT) nanocomposites were investigated for the concentration effects on dispersion, glass transition, degradation, and mechanical properties. Samples were prepared using a controlled torque stirrer and slow solvent extraction was followed for the cast samples. Optical microscopy shows that the surface of the cast sample has increased edge–edge clay platelet attraction. Transmission electron microscopy of the through thickness sample indicated platelet edges, increased face–face coagulated states and some edge–edge flocculated states of tactoid formation. X-ray diffraction indicated that for 1% sample a highly exfoliated structure was obtained while between 1.5 and 3% intercalated and exfoliated dispersions were obtained. The glass transition was not significantly affected by clay presence but a drop in specific heat change was observed for all samples showing a 001 clay peak presence. The first heating scan showed PAI solvent and MMT organic emission but these emissions did not affect the PAI chemically. Degradation was altered by the level of matrix shielding by the clay. Hardness values were increased with clay presence but unaffected by concentration.

Nylon 6 and Montmorillonite Layered Silicate (MLS) Nanocomposites

Reducing the high gas permeability of plastic packaging is of serious concern for a variety of applications in food packaging and microelectronics arena. In the development of high altitude scientific balloons, the potential for unmanned mission success is critically related to the improvement in helium barrier capability. Separately, the introduction of expandable smectite clays, such as montmorillonites, into polymers has resulted in improved barrier properties. Here we investigate the mechanical properties and helium permeability of dispersed montmorillonite-layered silicates (MLS) in nylon-6 nanocomposite films. A 20 wt% MLS in nylon-6 master batch was prepared in a twin-screw extruder and then mixed with nylon to produce nylon MLS nanocomposites with MLS content ranging from 1 to 5% for testing. The nylon nanocomposites were extruded into films. A highly exfoliated dispersion in different films was determined using X-ray diffraction. Nylon-6 nanocomposites showed formation of -crystalline form, which was absent in neat nylon-6. Differential Scanning Calorimetry (DSC) confirmed the crystallinity change and the role of MLS as an additional nucleation contributor. The glass transition and mechanical properties were related to the nucleation capabilities of MLS. Increase in the degree and type of crystallinity together with tortuous path development due to exfoliated dispersion were the primary reasons behind the improvement in gas barrier properties of exfoliated nylon-6 nanocomposites.

High sensitivity gas permeability measurement system for thin plastic films

We have developed a system to quantitatively measure the permeation of gases through thin flexible substrates with high sensitivity. The system consists of two chambers, a high pressure side and an ultrahigh vacuum (UHV) side, separated by the flexible sample to be analyzed. The system is calibrated using a combination of a National Institute of Standards and Technology traceable calibrated He leak and a variable aperture calibrated orifice. The base total pressure for the UHV side is 1–3×10−10Torr. The partial pressure of individual gases that we are studying is <10−10Torr. The sample to be measured is secured between the two chambers using two 2.75 conflat flanges, two copper gaskets, and two indium “O” rings. The key factors that impact sensitivity and quantification are (1) reducing the residual partial pressure of the gas of interest to as low a value as possible on the UHV side of the system, (2) sealing the plastic sample between the two chambers with no detectable gas leakage around the sample or ...