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[GreenYes] Re: plastics recycling education
In answer to your question below about the different melt indices of HDPE:
polyethylenes such as HDPE, PP and LDPE can be either blow mold or injection
grade resin.

Blow mold grades have something called their "melt index" less than one
(sometimes referred to as fractional melts), and injection grades more than
one, but typically >10.

In simple language, melt flow is just a measure of how gooey vs. runny the
resin is.  To hold in its liquid state against the sides of a bottle mold,
the resin must be gooey.  To flow easily into and through the cavity of a
mold to make a cap, yogurt cup or ice cream pail, it must be runny.

Except for very low end applications such as flower pots and unrated plastic
lumber, the end markets will only accept HDPE that is either blow or
injection -- the two cannot be mixed.  And for applications the melt flows
will need to be only low or very high flows to be accepted.

In retrospect, it is unfortunate that the original SPI codes assigned no. 2
to both blow and injection, but there you go, hey?


----- Original Message -----
From: "melissa terry" <>
To: "Peter Anderson" <>; <>
Sent: Monday, January 07, 2002 3:24 PM
Subject: plastics recycling education

dear recyclers,

while we're on the sticky subject of plastics, does
anyone know if there is ANY educational material
available out there that explains the difference
between blow-molded and injection-molded plastics?

i have visted with the american plastics/chemistry
council and with the napcor folks to no avail. i'm
specifically looking for a poster or something to help
explain why, because of their different markets, we
cannot accept all #1's and #2's in our program at this

any leads would be greatly appreciated!

melissa terry

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