How does recycling plastic affect its tensile strength?
The core process of mechanically recycling thermoplastics is heating and then cooling. I was wondering if this would cause the plastic to become weaker by continuously breaking the intermolecular forces between the polymer chains. To test this I heated LDPE in the oven then tested tensile strength by hanging a bucket from it and adding gravel until it broke. I found that after heating, the tensile strength had actually increased. I did the same with HDPE, and found that after heating, the strength decreased but after heating again, the strength increased. It appeared that as LDPE is fairly amorphous (weaker) heating made it more crystalline (stronger.) HDPE is more crystalline, so heating made it more amorphous and heating again made it back to being stronger. However, the experiment lacked reliability and accuracy due to lack of precise equipment. It would be worth testing with the extrusion machine to get uniform thickness as well as finding out the effects over many times recycled.
researchHDPEmeltingLDPE
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