Using Internet Superpowers...From the manufacturer:
Q: Is it possible to bond or glue two pieces of Coroplast together?
A: Polypropylene is great for many uses due to the fact that it is resistant to chemicals; unfortunately the same properties make it difficult to bond using chemical bonding agents. However, several products have been developed recently by companies such as 3M that are designed to bond polypropylene structurally. Coroplast has not yet tested these products fully. 3M's Scotch-Weld™ Structural Plastic Adhesive DP-8005 is available from Grainger and other distributors for industrial use.
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