Engineering Resins and Their Blends

The term engineering polymer is applied to a processable resin, capable of being formed to precise and stable dimensions, having high performance at CUT? 100°C, and the tensile strength of ? ? 40 MPa . Five polymer families belong to this category: Polyamides (PA), Thermoplastic Polyesters (PEST), Polycarbonate (PC), Polyoxymethylene (POM), and Polyphenyle Ether (PPE).

Engineering resins and their blends have been foamed:
1- Using mainly chemical foaming agents, e.g.,hydrazodicarboxylates, benzazimides or 5-phenyltetrazole. However, products of decomposition of these agents (e.g., alcohol, ammonia, water, etc.) were found to hydrolyze PC, PA, PC/ABS, or PEST, reducing the performance of foamed products.
2- For this reason, dihydrooxadiazinones were proposed as the preferred
chemical foaming agents for the engineering resins, their compositions and blends.

Dihydrooxadiazinones

3-Another method for foaming high temperature polymers profits from
thermal instability of polypropylene carbonate (PPCO, MW = 1 to 1000 kg/mol).



The process involves blending PPCO with a resin or its blend that is to be foamed. The blend is then heated to T > 300°C, sufficient to melt the principal resin and to decompose PPCO.
Talc, wollastonite, clay, CaCO3 or citric acid can be used as a nucleating agent. The densities of the molded articles were reduced by at least 50%.

4- Most recently, foaming of the engineering resins by supercritical CO2 was introduced.
1- Polyamides (PA):
Polyamides are abbreviated as PA-, followed by the number of carbons in a di-amine and dicarboxylic acid, viz. PA-66 has six carbons in each component, etc.
- Poly-?-caprolactam or polyamide-6 (PA-6) was first studied by Von Brown in 1905-10, and 30 years later commercialized as Perlon™.
- In the year 1936, PA-66 and several other aliphatic and semi-aromatic polyamides were disclosed
- Two years later, DuPont introduced Nylon™, an aggregate of New York and LONdon.