Without "they would," the meaning is unclear because the sentence would seem to say that the time the plastics take to dissolve was simply longer than it originally seemed. In other words, the measurement of the time needed to dissolve was somehow clarified and found to be longer than the measurement first appeared to be. The actual meaning of the sentence is that there was some prior expectation that the plastics would take less time to dissolve.
You might also try asking yourself, "something took more time than WHAT originally seemed?" Was it simply that the measurement of the time was greater than it originally appeared to be or was "the time they would take to dissolve" more than originally expected. The intended meaning is the latter.
Note also that the verb "take" is left off the end of the sentence. It is implicit.
Hope this helps!
Stuart Park
Simply Brilliant
Stuart is a Harvard grad GMAT expert who scored 760 the first time he took the exam, with 99th percentile quant and verbal scores. He has extensive experience teaching for one of the "elite" GMAT prep companies. Through
https://www.simplybrilliantprep.com he offers online classes, private tutoring and MBA application consulting for clients worldwide.
