Process Economics Program Report 78
Published: August 1972
This report is primarily concerned with thermoplastic materials having an acrylonitrile (methacrylonitrile) content of 50%w or greater. They may be copolymers, grafts of copolymers onto a rubbery substrate, or blends of homopolymers and/or copolymers. With so many possible variations in composition and properties, acrylonitrile thermoplastics include a large family of materials that can be converted into fibers, films, and molded articles.
Resins that are truly thermoplastic and can be molded into finished articles are emphasized in this report. The high-acrylonitrile (often over 85%) blends that are used in some synthetic fibers do not have the processability of a true thermoplastic. Therefore, resins intended primarily for use in spun fibers (or cast film) are not included in this report. A number of special techniques have been disclosed* that are said to permit the molding of shaped articles from very-high-acrylonitrile resins. But, since we do not know if these techniques are being practiced, we have not evaluated them for this report.
A high nitrile content confers outstanding barrier properties on thermoplastic materials. Films and articles produced from these barrier resins have unusually low permeability to both water vapor and common gases, such as oxygen, nitrogen, and carbon dioxide, Only polyvinylidene chloride (Saran) has comparably low permeabilities to both water vapor and gases. Most thermoplastics with low gas permeability are not good moisture vapor barriers, and vice versa.
High-nitrile barrier resin compositions that are similar to grafted ABS resins are now being developed. Two such compositions are evaluated in this report. They combine processability and transparency with reasonably high impact strength and high heat-distortion temperature. Techniques have been examined for converting pellets of these resins into finished articles.
Acrylic multipolymers are another class of resins, similar to clear ABS resins. They are becoming established in the food container field. Although they contain only 10 to 11%~ acrylonitrile, they have some of the barrier properties of the acrylonitrile thermoplastics, and may be expected to compete for many of the same applications, excepting highly carbonated beverages. An evaluation of acrylic multipolymers, of which Cyanamid's XT® resin is the best example, is included in this report to permit comparison between the acrylic multipolymers and the newer high-nitrile thermoplastics.