Blending spherulite size

The morphology of the spherulites was in the form of a Maltese Cross , which was confirmed by the Avrami exponent value in the DSC study. The spherulite size of the binary blends was smaller than that of pure PET and PEN. 

The structure of crystalline polymers may be significantly modified by the introduction of fillers. All aspects of the structure change on filling, crystallite and spherulite size, as well as crystallinity, are altered as an effect of nucleation [9]. A typical example is the extremely strong nucleation effect of talc in polypropylene [10,11], which is demonstrated also in Fig. 2. Nucleating effect is characterized by the peak temperature of crystallization, which increases significantly on the addition of the filler. Elastomer modified PP blends are shown as a comparison crystallization temperature decreases in this case. Talc also nucleates polyamides. Increasing crystallization temperature leads to an increase in lamella thickness and crystallinity, while the size of the spherulites decreases on... 

It should be pointed out that there is no direct physical relation between the phenomenon of fractionated crystallization and the number and the size of spherulites in the pure polymer. Whereas the occurrence of fractionated crystallization is related to the ratio between the number densities of dispersed polymer particles and primary nuclei, the size and the number of spherulites are additionally influenced by the cooling rate and the crystallization temperature. There is, therefore, also no relation between the fractionated crystallization and the type of the arising crystalline entities (complete spherulites, stacks of lamellae,...) both in the pure and in the blended material. There is, finally, no relation between the scale of dispersion which is necessary for the occurrence of fractionated crystallization and the spherulite size in the unblended polymer. 

The reverse could be observed in a compatibil-ized blend. Because in these blends a serious decrease of the spherulite size was observed, the authors concluded that the compatibilizer... 

The thermal and morphological behaviors of PP/EPDM blends were studied by Da Silva and Coutinho (6) using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. Crystallization kinetics of PP/ EPDM blends were found similar. Ten to twenty weight percent addition of EPDM resulted in increasing of spherulite size (Fig. 14.3). Heat of fusion and crystallinity degree of PP/EPDM systems decreased when EPDM contents were increased. 

PA-6/EPR + g-SA Compatibilization 1 spherulite size (which was not found in PA-6/EPR blends) + serious ( of the interfacial adhesion Strong nucleatimi effect of EPR-g-S A on the PP phase Martuscelli (1984)... 

Wilfong et al. (1986) reported on the effects of blending low concentrations (1-10 wt%) polyolefin with PET on the crystallization and toughening behavior of the latter. The authors studied blends of PET with LLDPE, HDPE, PP, and poly (4-methylpentene-l), all of them having a lower melting point than PET (Table 3.15). Polyolefin melts did not enhance the nucleation of PET, although the spherulite size of the PET matrix was found to be 2.5-3 times larger than for the homopolymer, with a broader spherulite size distribution. Both the crystallization... 

The higher-order structures (morphologies) of injection-molded polypropylene (PP), which should be considered, are crystalline form, lamellar thickness, spherulite size, crystallinity, molecular orientation, crystal orientation, dispersion state of a blended polymer, length and orientation of reinforcing fibers, crystalline texture (skin-core structure), etc. 

Most PE/PP blends show a two-phase structure that may be detrimental to blend performance at large strains. Blending enhances the crystallinity and reduces the spherulite size, which may improve performance especially at small deformations, viz. increased modulus, where the effect of immisdbility is small. However, at large strains poor adhesion between the two phases results in a low value of the stress and... 

Fig.65. Development of spherulite size ( ) with time for PCL crystallisation in blends with SMA with 90 wt % PCL, (A) SMA-14 and (O) SMA-25 taken from [148]...

Cross-links Highly ordered structures Crystallinity Crystalline thickness Spherulitic size and morphology Orientation Hybridization (blends and composites) Material Morphology Material shape and dimensions Porosity and pore size Surface Treatment Coating Alkaline treatment Stress or strain... 

In a few cases, the addition of minor amounts of immiscible or miscible polymers results in the nucleation of a crystalline polymer. The nucleation of PP by PE and polyamides (e.g., PAl 1) (immiscible) as well as the addition of PP to poly(butene-l) (miscible) has been noted in the literature [138-141 ]. The addition of LDPE to PP showed a reduction in the spherulite size of PP, attributed to an increase in nucleation density of the a-crystalline form along with an increase in the rate of growth of the -crystalline form [141]. The nucleation of polycarbonate by the zinc salt of sulfonated polystyrene ionomers was noted to occur with both miscible and phase separated blends [142]. Nanometer sized ionic aggregates appeared to contribute to the polycarbonate nucleation. A liquid crystalline copolyesteramide (Vectra-B950 ) was shown to accelerate the crystallization of poly(phenylene sulfide) [143]. This effect was not concentration dependent and did not change the level of crystallinity. 

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