Here "instead of getting PC cases primarily from metal/wood/glass/paper, which can be recycled or re-purposed, we get 99,9% plastic PC enclosure.
You have an appositive phrase declaring the indirect subjects in the dependent clause, metal/wood/glass/paper, are recyclable unlike the direct subject of the independent clause, plastic.
Rearranging the clauses so they're not backwards.
"We get 99.9% plastic enclosure instead of getting PC cases primarily from metal/wood/glass/paper which can be recycled or repurposed."
Is it no implied that plastic cannot be recycled or repurposed?