The Crystallization And Melting Behavior Of Polymer Materials Under The Isothermal Environment

Polymer crystallization and melting behavior were strongly affected by manyfactors, and the temperature, film thickness, and the second components play animportant role during the crystal growth process and in the melting behavior, andeventually affect crystal morphology In this thesis, the growth, morphology and themelting behavior of poly(3-hydroxybutyrate)/poly(methylmethacrylate)(PMMA) blendwas investigated by Polarizing optical microscope (POM), differential scanningcalorimetry (DSC), X-ray wide-angle diffraction (WXRD) and other instrumentsisothermally, respectively.In the same composition ratio, different crystallization temperature and filmthickness, the spherulite structure and morphology of PHB/PMMA blending system wasstudied by Polarizing optical microscope (POM). Study found that PHB/PMMA blendspherulite morphology under isothermal condition was similar to pure PHB, also at arelatively low temperature and high temperature observed non-banded spherulite, and inthe middle of the crystallization temperature observed banded spherulite. In addition,compared with pure PHB, the PHB/PMMA blend system formed the banded spherulite inthinner thickness and lower crystallization temperature. This is because of the addition ofPMMA, reduceed the diffusion rate of PHB. This suggested that the banded spheruliteformation mechanism of PHB/PMMA blend system is same as pure PHB. It wasconsidered that a depletion zone appeared periodically at the crystal growth front due tothe slower diffusion rate which resulted in the formation of banded spherulite.In the same crystallization temperature and film thickness, different compositionratio, the spherulite structure and morphology of PHB/PMMA blending system wasstudied by Polarizing optical microscope (POM). Research showed that: after addingPMMA amorphous component, the regularity of the band spherulites of PHB decreased,and with the increase of the content of PMMA, the regularity of the banded spherulitesdecreased more. In addition, with the increase of PMMA, blending system spherulitespacing decreased. According to the experimental results, we think the regularity of the blending system of PHB band spherulite decline is due to the influence of the addition ofPMMA, and due to the amorphous component content PMMA was less and PHBinteracted with PMMA is small, so PMMA was concentrated on PHB wafer mezzaninearea, the crystal morphology do not change the state of aggregation structure, just thePHB banded spherulite structure become irregular. Along with the increase of the contentof PMMA, the greater the PHB molecular diffusion rate is blocked, the smaller the rate ofdiffusion, the smaller the loss of frontier area growth, therefore, the band spacing issmaller.The melting behavior of blending system was studied by Polarizing opticalmicroscope (POM), differential scanning calorimetry (DSC), X-ray wide-anglediffraction (WXRD). Results show that when the content of PHB (Wt/Wt) greater than80%, the blend system was partly compatible, and when PHB blend of PHB/PMMAcontent less than70%(Wt/Wt), blending system can not be observed crystal formation.PHB in its high critical temperature isothermal crystallization occured when spherulitecrystal first, long-term placed on melting behavior and disappeared. This is due to thecritical temperature to generate the banded spherulite in metastable, if under thistemperature place for a long period of time, will take the initiative to crystallization andmelting process of dynamic balance, through the molecular thermal motion so as toachieve a new balance, so, ordered the banded spherulite slowly disappear. Besides,due tothe discontinuous spherulite growth, the thickness of the spherulite from center to edge isreduced, in turn, the smaller the thickness of the spherulite morphology is unstable, sospherulite disappear when the thickness of smaller chip to the thickness of outer biggerspherulite centers gradually disappear.