Recommended ratio of PU to PET regrind for load bearing composite?

PET regrind is inexpensively available (around $0.15/lb, bulk), but difficult to work with. One of the few adhesives that will
bond well with PET is PU, so I would like to try making up batches of PET/PU composite, casting them into plates, and using them around the home and shop for various static and dynamic load bearing tasks, just to see how well they fare.
PU-based adhesives are expensive (about $6/lb, in moderate bulk), so if too much is required to bind the PET regrind into an effective composite, the advantage of using inexpensive PET will be lost. Looking at composites of crumb rubber and PU, I see that around 5% PU elastomer adhesive is considered sufficient to duplicate the properties of whole natural rubber.
The PET flakes are significantly larger than rubber crumbs, so I will probably need less PU, but how much less is a reasonable amount? Lacking better information, I will just try making three different batches with 1%, 3%, 5%, and see how they turn out. I don't want to use more PU than necessary, to minimize cost.
Suggestions would be welcome. -- TTK
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Shop around some more for cheaper PU, you ought to be able to find a lower price. Rather than a PU adhesive, look at formulations designed for casting, the adhesive properties of most PU compounds should be adequate for your purposes.-Jitney
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