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 havebeen foamed:
1-Using mainly chemical foamingagents, e.g.,hydrazodicarboxylates, benzazimidesor 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 performanceof foamed products.
2- For this reason, dihydrooxadiazinoneswere proposed as the preferred
chemical foaming agents for the engineering resins,their compositionsand blends.
Dihydrooxadiazinones
3-Another method forfoaming high temperature polymers profits from
thermal instability of polypropylene carbonate(PPCO, MW = 1 to 1000kg/mol).
The process involves blending PPCO witha resin or its blend that is to be foamed. The blendis then heated to T > 300°C, sufficient to meltthe principal resin and to decompose PPCO.
Talc,wollastonite, clay, CaCO3 or citric acid can beused as anucleating agent. The densities of themolded articles were reduced by at least 50%.
4- Most recently, foaming of the engineering resinsby supercritical CO2was introduced.
1- Polyamides (PA):
Polyamides are abbreviated as PA-, followed bythe number of carbons in a di-amine and dicarboxylicacid, viz. PA-66 has six carbons ineach component, etc.
- Poly-?-caprolactam or polyamide-6 (PA-6) was first studied by Von Brownin 1905-10, and 30 years later commercialized asPerlon™.
-In the year 1936, PA-66 and several other aliphatic and semi-aromatic polyamides were disclosed
- Two years later, DuPontintroduced Nylon™, an aggregate of New Yorkand LONdon.
-PA-11 was commercialized in 1955,
-PA-12 in 1966,
-PA-612 in 1970,
-PA-46in 1987.
-In 1976 DuPont started pro
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