High pressure crystallization and resulting polymorphic composition of long chain branched polypropylene (LCB-PP) was studied and compared with common linear isotactic polypropylene (PP). Commercially available LCB-PP and PP with similar melt flow indexes were crystallized under several high pressures (20, 40, 80, 120 and 160 MPa) at constant cooling rate 5 °C min -1 . Structure of crystallized samples was evaluated via wide angle X-ray scattering, differential scanning calorimetry and scanning electron microscopy. It was shown that under low pressure LCB-PP crystallizes at higher crystallization temperature than PP due to its higher nucleating density. The opposite situation is observed at high pressures (120 and 160 MPa): crystallization temperature of PP exceeds that of LCB-PP as a negative effect of branching is pronounced. Polymorphic analysis proved that LCB-PP tends to crystallize into orthorhombic γ-form. This crystalline form becomes to be dominant at 40 MPa and LCB-PP samples crystallized at 120 and 160 MPa contains solely γ-form. On the other hand, no pure γ-form sample was prepared from PP in this study, although positive effect of pressure on its formation is observed. Thermodynamic stability of LCB-PP crystalline structure is systematically lower compared to PP. With pronounced crystallization pressure, the melting peak broadens and finally splits indicating presence of dominant amount of γ-form in LCB-PP. In comparison with PP, crystallites in LCB-PP structure are considerably smaller due to lower crystal growth rate and higher nucleating density.
Response to Reviewers:Dear editor, according to your recommendation, we have reduced the similarities in the manuscript text. I have also corrected the title to Long chain branched polypropylene: Crystallization under high pressure and polymorphic composition.We hope that you will find the revised manuscript suitable for publication in Journal of thermal analysis and calorimetry.
This article deals with the measurement of the mechanical properties of a filled poly (butylene terephthalate) (PBT+35 % GF (glass fibres)) surface layer modified with beta radiation. Injection-moulded test bodies were subsequently irradiated with beta radiation using doses of (0, 33, 66 and 99) kGy. The measurement of the mechanical properties was realized with an ultra nano-hardness tester. The results of the measurements showed a considerable increase in the micromechanical properties (indentation hardness, indentation elastic modulus) when low doses of beta radiation were used. The aim of this paper is to study the effect of ionizing radiation at different doses on the ultra nano-hardness of the surface layer of poly (butylene terephthalate) (PBT) and compare these results with those for non-irradiated samples. The study was carried out due to the ever-growing use of this type of polymer, poly (butylene terephthalate) (PBT). Keywords: poly (butylene terephthalate) (PBT+35 %GF), surface layer, mechanical properties, ultra nano-hardness V~lanku avtorji opisujejo mehanske lastnosti s steklenimi vlakni oja~anega polibutilen tereftalata (PBT+35 % steklenih vlaken (GF)) po radioaktivnem obsevanju g. Injekcijsko brizgani preizku{anci so bili obsevani z dozami (0, 33, 66 in 99) kGy radioaktivnega sevanja g. Lokalne mehanske lastnosti na povr{ini preizku{ancev so dolo~ili z avtomatskim merilnikom ultra nanotrdote. Rezultati meritev so pokazali znatno povi{anje mikromehanskih lastnosti (nanotrdote in elasti~nega modula vtiskovanja)`e pri nizkih dozah obsevanja vzorcev. Namen tega prispevka je prikazati vpliv ionizirajo~ega sevanja razli~nih jakosti na ultrananotrdoto povr{inskih plasti PBT+35% GF in primerjavo z neobsevanim vzorcem. Raziskava je bila izdelana zaradi vse ve~je uporabe tega polimernega materiala v pogojih ionizirajo~ega sevanja. Klju~ne besede: polibutilen tereftalat, oja~an s 35 % steklenih vlaken (PBT+35 %GF); povr{inska plast, mehanske lastnosti, ultrananotrdota
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