Abstract
The shear-induced and cellulose-nanofiber nucleated crystallization of two novel aliphatic–aromatic copolyesters is outlined due to its significance for the in situ generation of biodegradable nanocomposites, which require the crystallization of nanofibrous sheared inclusions at higher temperatures. The shear-induced non-isothermal crystallization of two copolyesters, namely, poly(butylene adipate-co-succinate-co-glutarate-co-terephthalate) (PBASGT) and poly(butylene adipate-co-terephthalate) (PBAT), was studied following a light depolarization technique. To have a deep insight into the process, the effects of the shear rate, shear time, shearing temperature and cooling rate on the initiation, kinetics, growth and termination of crystals were investigated. Films of 60 μm were subjected to various shear rates (100–800 s−1) for different time intervals during cooling. The effects of the shearing time and increasing the shear rate were found to be an elevated crystallization temperature, increased nucleation density, reduced growth size of lamella stacks and decreased crystallization time. Due to the boosted nucleation sites, the nuclei impinged with each other quickly and growth was hindered. The effect of the cooling rate was more significant at lower shear rates. Shearing the samples at lower temperatures, but still above the nominal melting point, further shifted the non-isothermal crystallization to higher temperatures. As a result of cellulose nanofibers’ presence, the crystallization of PBAT, analyzed by DSC, was shifted to higher temperatures.
Highlights
Due to recent increased awareness about the global environment, a new concept of in situ generation of all-polymeric biodegradable nanocomposites has been developed, where the nanofibers of one biodegradable polymer are formed inside a second biodegradable polymer during melt compounding
The concept has been applied to a range of biodegradable polymers, namely, polylactide (PLA), polyhydroxyalkanoate (PHA), poly(glycolic acid) (PGA), poly(butylene adipate-co-terephthalate) (PBAT), biobased polyamide (PA), poly(1,4-butylene succinate) (PBS) and poly(ε-caprolactone) (PCL), to fabricate sustainable, green, all–polymer nanocomposites in a single stage
Studying the effect of cellulose nanofibers (CNFs) on the non-isothermal crystallization behavior of PBAT is of great importance for the in situ generation of hybrid all-polymeric biodegradable nanocomposites, where the crystallization temperature of PBAT nanofibrous sheared inclusions could be further shifted to higher temperatures due to the presence of cellulose bio-nanofibers
Summary
Due to recent increased awareness about the global environment, a new concept of in situ generation of all-polymeric biodegradable nanocomposites has been developed, where the nanofibers of one biodegradable polymer are formed inside a second biodegradable polymer during melt compounding. Studying the effect of cellulose nanofibers (CNFs) on the non-isothermal crystallization behavior of PBAT is of great importance for the in situ generation of hybrid all-polymeric biodegradable nanocomposites, where the crystallization temperature of PBAT nanofibrous sheared inclusions could be further shifted to higher temperatures due to the presence of cellulose bio-nanofibers. This idea stems from the recent studies reporting that CNFs could act as crystal nucleating agents, increasing the number of crystals and decreasing the crystal sizes for the non-isothermal crystallization of biodegradable polymers [24]. Cellulose nanofibers (CNFs) with diameters between 10 and 20 nm and lengths of 2 to 3 μm, obtained from Nanografi (Ankara, Turkey), were employed to enhance the crystallization of PBAT
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