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Does anyone have a good definition of brittle and hard plastics?


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#1 glendora

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Posted 18 June 2013 - 01:25 AM

Does anyone have a good definition of brittle and hard plastics?  Thanks!



#2 esquef

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Posted 18 June 2013 - 02:21 PM

This is a complicated question. With plastics hardness doesn't necessarily equate to brittleness.

 

For example a commonly used clear plastic used in processing areas is polycarbonate. The reason is that it's hard but has high tensile strength and relatively high elongation properties. These properties impart shatter resistance.

 

On the other hand is acrylic (brand names: Plexiglass, Lucite, ACRLITE, Perspex). Again, hard and clear but acrylic has relatively low tensile strength and elongation properties and low elongation properties. These properties mean that acrylic shatters easily when struck by a load or force.

 

Other shatter resistant plastics (mostly opaque or transluscent) include polypropylene, polyethylene and nylon. There are many more of course.

 

Plastics that can be shatter-prone could include styrene, non-plasticised PVC, and to a lesser degree ABS.

 

One other point: even shatter resistant plastics will shatter if your manufacturing process includes low temperatures. Another measurable property of plastics is Glass Transition Temperature (Tg). An example of how Tg effects shatter resistance: polypropylene has a Tg of between -20 and 0 degrees C, so it can easily lose its molecular mobility and become shatter-prone in low temperature environments.

 

I've attached a "Periodic Table for plastics" which lists a host of plastics and includes tensile strength, elongation, and Tg for each. It's a lot of complicated info, but might be helpful in performing risk analyses and choosing a particular type of plastic in the design of your production process.

 

http://www.pcn.org/T...of Polymers.htm



#3 Harminnie

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Posted 20 June 2013 - 01:28 PM

Our BRC auditor pretty much cleared the definition up for us, kind of, well maybe-not!  Basically we were told "it is any glass or plastic that 'could' break".  We concluded that anything "could" break, so we decided to keep it simple and listed every piece of glass and plastic we could find.  Some are audited more frequently than others based on risk analysis.  We included covers on clocks, plastic covers on warning lights, plastic covers on gauges, light covers on forklifts, etc.  Hope this cleared it up for you :)  Have fun!



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#4 Charles.C

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Posted 20 June 2013 - 04:37 PM

Dear All,

 

Perhaps it is relevant to add that the usual objective in defining brittle / hard plastic on this forum is with respect to the potential risk of a FS related event. AFAIK, it is not intended to include every item of visible plastic although the enthusiasm is creditable .

 

eg these threads -

 

http://www.ifsqn.com...rittle-plastic/

(maybe, scope debatable,  post #8)

 

http://www.ifsqn.com...s-hard-plastic/

 

Would have expected a BRC auditor to make an FS  connection also.

 

Rgds / Charles.C


Kind Regards,

 

Charles.C





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