Crystallization isothermal crystalhzation

It is of particular importance that the surface of iPP crystals isothermally crystalhzed at various temperatures is not smooth, resulting in the black and white periodicity observed via optical microscopy, which is ascribed to the formation of undulations with interrupted edges. That is to say, undulations can be observed not only in sPP single-crystal lamellae, but also in iPP crystals, though in the different sector. 

Crystalhzation studies in blends of iPP/POE reveal that the crystallization process of iPP is affected by the addition of POE and vice versa. It has been demonstrated how the POE promotes the nucleation and crystal growth processes of iPP, this effect being more appreciable at low POE concentration (< 10 wt% POE). Analysis of the crystallization kinetics of the iPP crystals isothermally crystallized at different temperatures in blends of iPP/POE is supported by the morphological observations (lamellae, dendritic, and eventually spherulitic texmres) through optical microscopy. 

Figure 7.25 (a) Optical micrographs and (b) AFM phase images displaying the crystalline morphologies of the 30/70 ePP/POE blend isothermally crystalhzed at various temperatures (AFM images are carried out at room temperature after the samples were crystallized at a preset for a certain time and subsequently cooled to room temperature, while the optical micrographs are taken at certain temperatures). 

For the isothermal crystalhzation stndies, samples are rapidly cooled to the crystallization temperature (e.g., 50°C/min.) and kept at the crystallization temperatme. For non-isothermal crystalhzation studies, samples are cooled with a selected rate (for example, 3, 5, 10, or 15°C/mia to the selected crystalhzation temperatrrre and then held at the crystallization temperature for a selected period of time (e.g., 5 mia). ... 

This is a new bacterial thermoplastic and is an ideal model substance for crystalhzation studies. Burham, Keller, Otun, and Holmes found that the crystals always thicken logarithmically with time when heated above original crystallization temperature, but synchrotron radiation has shown that is does not thicken in situ during isothermal crystallization from the melt. This is true even at temperatures where one can observe thickening of lamellae which had previously been crystallized at lower temperatures. 

The non-isothermal crystallization dynamics were performed using DSC, employing coohng rates of 2.5, 5, 10, 20, 25, 30, 35 and 40°C/min. The isothermal crystallization dynamics were studied for each sample heated to 290 °C, with a 5 min hold time, and cooled to the isothermal crystallization temperature using a coohng rate of 200°C/min, and tlien holding for 40 min to obtain the crystalhzation exotherm. 

The addition of ionic plasticizer such as sodium salt of dodecylbenzenesulfomc dramatically increases the ability of the ionomer to ciystallize. Figure 11.11 shows that the heat of fusion of an isothermally crystallized ionomer increases with the addition of a plasticizer. This behavior is attributable to the separation of ionic domains, which enhances the molecular mobility of the crystalhzable chains and also increases the crystallization rate as the amount of plasticizer increases. " ... 

A drawn film was also included in the analysis [66]. The quasi-isothermal TMDSC of this drawn sample is reproduced in Fig. 6.109. It was produced out of practically amorphous PET by biaxial drawing at 368 K. The sample retains no residual cold crystalhzation and has a higher rigid-amorphous fraction than the semicrystalline reference PET of Fig. 3.92. Long-time aimealing causes an aimealing peak of the crystals, as described in Sect. 6.22, but displays no hysteresis peak, as was also observed for the slowly cooled, undrawn PET samples with similar crystallinity used as an example in Fig. 6.129. 

Isothermal crystallization experiments using DSC support the idea that the crystalhzation behavior of thin PODMA lamellae in P(S—6—ODMA) block copolymers is comparable to that of PODMA homopolymers. The... 

The overall nucleation and crystalhzation rates of PLA tmder heterogeneous conditions are relatively higher than in homogenous conditions. The nucleation and crystallization rates of propylene-ethylene copolymer are increased tmder isothermal conditions. Addition of nucleating agent accelerates crystallization. Avrami equation is in popular use in the analysis of isothermal crystallization kinetics of polymers ... 

The exfoliated graphite dramatically modified the non-isothermal crystallization behavior of the PP matrix, increasing the crystalhzation temperatirre, crystalhzation rate,... 

The melting temperature-composition relations that were described above were for rapidly crystalhzed samples. This crystallization procedure results in relatively small crystallite sizes. In an alternative procedure the crystallization can be conducted isothermally at elevated temperatures and never cooled prior to fusion. It is then found that the melting temperatures are dependent on the nature of the comonomer.(79) Ethylene butene and hexene copolymers behave similarly to one... 

Equation 9.28 can be used to describe the kinetics of non-isothermal crystallization process imder quiescent conditiom However, the crystallization process in the spinning filament is non-quiescent, and the molecular orientation developed imder the tensile stress affects the crystallization rate. Therefore, the traditional non-isothermal crystallization rate, K T), must be replaced with the non-isothermal, stress-induced crystalhzation rate, K T,J), where / is the orientation factor. K T,J) also is called the total crystallization rate. With the total crystallization rate, Equation 9.28 can be rewritten to give ... 

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