Can anyone give me a primer on plastics used

December 24, 2005

I am bewildered by the number of different terms:

celluloid,

cellulose acetate

cellulose nitrate

resin

bakelite

lucite

casein

and there must be others.

Any chemists or material scientists out there that can provide basic information that a layman can understand?

Regards,

Jeen

December 24, 2005

Jeen,

Celluloid is used as a generic term for both cellulose acetate and cellulose nitrate, though technically it was a trademark name for cellulose nitrate.

Cellulose nitrate was one of the first plastics available and was used by many pen manufacturers as a successor to hard rubber. Sheaffer's jade green Radite is a common example of cellulose nitrate. Cellulose nitrate quickly fell out of favor because of it's inherent color instability and extreme flammability. It was also used for picture and movie film.

Cellulose acetate was a more successful version of "celluloid", being more stable when colored and far less flammable, but was still not as stable as modern plastics of today. This was also (and I believe still is) used for picture and movie film.

Bakelite is a trademarke name for phenol formaldehyde resin, also known as phenolic resin or phenolic plastic, or simply phenolic. I've never seen any pens actually made of Bakelite, though many antique dealers automatically assume any old plastic is Bakelite. Bakelite was used for many pen related items, though, such as inkwells, blotters and letter openers.

Resin is a generic term for any plastic or rubber-like material that uses unsaturated polyester resin as the chemical binder to hold it together.

Lucite is a trademark name for polymethyl methacrylate. It also has many other trademark names, such a Plexiglas, Plastic Glass and Acrylite, but is most commonly called acrylic glass, acrylic plastic or simply acrylic. I think the first commercially available pen made of acrylic was the Parker 51. Although celluloid could be injection molded, it was a very difficult process, and acrylic was one of the first plastics that was easily injection molded.

Casein is technically a protein found in milk, and is used to make a variety of things, from plastics to glues to dietary supplements. Casein plastic was used in some pens, though not as widely as some people will have you believe. It was widely used to make knitting needles, and most high end (and expensive) knitting needles are still made of casein. It feels very nice in the hands, almost like ivory; in fact it was called artificial horn, because it looks and feels so much like ivory. Casein is one of the least stable plastics. It's kind of ironic that the 2 things that will destroy casein plastics are the lack of moisture and too much moisture. A lack of moisture causes casein to become brittle and prone to cracks, while too much moisture will soften it and cause it too swell and deform. This makes it an ideal plastic for knitting needles, where they never require soaking in water to clean and are held in the hands for long periods at a time, where they soak up the perspiration from the hands. It does not make a good plastic for pens, as all inks are water based and we usually soak the pens in water to clean the old ink from them.

Sorry about the length of the post, and a lack of specific pen examples made of each kind of plastic, but I hope this helps your understanding of different materials we generally call plastic.

Tom