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ABSTRACT This work investigated the effect of isophthalate (iso) content in poly(ethylene terephthalate) (PET) materials on its degree of crystallinity (χ%) and mechanical properties. Melt blends were prepared from virgin (0 iso-wt.%) and bottle-grade (1.7 iso-wt.%) PET and subsequently spun into fibers. The mechanical and crystallinity properties were determined using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and uniaxial tensile testing. The crystallinity results determined from DSC and XRD quantified the relationship between iso-content and χ% in the materials. It was found that melt-mixing of different isophthalate grades had a lesser effect on melting temperature (Tm) and χ% than chemically recycled random copolymers of terephthalate and isophthalate. It was further shown that random copolymers of <0.25 iso-wt.% had comparable crystallinity to the virgin high-modulus low-shrink (HMLS) materials. 

Abstract A surfactant-free oil-in-oil emulsion-templating method is presented for fabrication of monolithic polyimide aerogel foams using monomer systems that produce fast sol–gel transition. An aerogel foam is a high porosity (∼90%) material with coexisting meso- and macropores inherent to aerogels with externally introduced micrometer size open cells (macrovoids) that are reminiscent of foams. The macrovoids are introduced in polyimide sol using surfactant-free emulsion-templating of droplets of an immiscible liquid that are stabilized against coalescence by fast sol–gel transition. Three immiscible liquids – cyclohexane, n -heptane, and silicone oil – are considered in this work for surfactant-free emulsion-templating. The aerogel foam monoliths, recovered by supercritical drying, exhibit smaller size macrovoids when n -heptane and cyclohexane are used as emulsion-templating liquid, while the overall porosity and the bulk density show weak dependence on the emulsion-templating liquid.