I emailed Case about the original question - "What are Case yellow handles made of?". I was curious myself. rev_jch is right - they're Delrin.
They also gave me some interesting history along with the answer, so here's the response I received:
Dear Ryan;
Thanks you for your interest in Case knives. There have been three yellow
cover materials used in Case history; celluloid, composition and Delrin.
Case began using yellow plastic in the 1920's and it was celluloid at that
time. The composition that is listed above was used from about 1945 until
1960 at which time we changed to using DuPont Delrin. I don't have much
information about the composition material other than it was easier to work
with than the celluloid. DuPont developed Delrin in the early 1950's and
patented the formulation in 1956.
Delrin is an acetal resin that was developed by DuPont in their efforts to
supply customers with tough heat resistant metal substitute. "Delrin(r)
bridges the gap between metals and ordinary plastics with a unique
combination of strength, stiffness, hardness, dimensional stability,
toughness, fatigue resistance, solvent and fuel resistance, abrasion
resistance, low wear and low friction. This quote is taken directly from
the DuPont Website explaining the characteristics of Delrin.
I hope I have sufficiently answered your questions. [Stuff about Case Collector Club]
Best Regards,
Rich Brandon
Engineering Manager
W.R. Case & Sons Cutlery Co.
[phone # & email removed for privacy]