The crystallization rate of polyamide 11 has been quantified in a wide temperature range between 320 and 450 K, using fast scanning chip calorimetry and differential scanning calorimetry. Different mechanisms of crystal nucleation/growth have been identified at temperatures below and above 370 K, causing a bimodal distribution of the crystallization rate as a function of temperature. Crystallization at low supercooling is connected with formation of triclinic α-crystals of lamellar morphology and ringed/banded spherulites. At high supercooling, formation of pseudohexagonal δ′-mesophase is observed. Because of the high nucleation density at low temperature, growth of the δ′mesophase is nonspherulitic. The δ′-mesophase transforms on heating to α-crystals without affecting the superstructure. The study is completed by quantification of the cooling conditions to allow δ-crystal formation at low supercooling, δ′-mesophase formation at high supercooling, and complete vitrification of the melt. The interplay between nucleation density and mesophase formation according Ostwald's rule of stages is discussed as a consequence of immobilization of the amorphous phase/formation of a rigid amorphous fraction.
Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactide (PLA) with different PHBV/PLA weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) were prepared by melt compounding. Their mutual contributions in terms of thermal stability, flammability resistance, mechanical properties and rheological behavior were investigated. The study showed that the increase in PLA content in PHBV/PLA blends leads to enhanced properties. Consequently, thermal stability and flammability resistance were improved. Further, the rheological measurements indicated an increase in storage modulus and loss modulus of PHBV matrix by addition of PLA.
Summary: This work is aimed at studying the morphology and the mechanical properties of blends of low density polyethylene (LDPE) and poly(ethylene terephthalate) (PET) (10, 20, and 30 wt.‐% of PET), obtained as both virgin polymers and urban plastic waste, and the effect of a terpolymer of ethylene‐butyl acrylate‐glycidyl methacrylate (EBAGMA) as a compatibilizer. LDPE and PET are blended in a single screw extruder twice; the first extrusion to homogenize the two components, and the second to improve the compatibilization degree when the EBAGMA terpolymer is applied. Scanning electron microscopy (SEM) analysis shows that the fractured surface of both the virgin polymer and the waste binary blends is characterized by a gross phase segregation morphology that leads to the formation of large PET aggregates (10–50 µm). Furthermore, a sharp decrease in the elongation at break and impact strength is observed, which denotes the brittleness of the binary blends. The addition of the EBAGMA terpolymer to the binary LDPE/PET blends reduces the size of the PET inclusions to 1–5 µm with a finer dispersion, as a result of an improvement of the interfacial adhesion strength between LDPE and PET. Consequently, increases of the tensile properties and impact strength are observed.
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