Blending and crystallinity

ANALOGY BETWEEN POLYMER BLENDS AND CRYSTALLINE HOMOPOLYMERS... 

It is clear from the literature that PA 6/maleated elastomer/MMT nanocomposites show a decrease in the impact strength in the presence of clay compared to the pure blend this decrease in the impact strength depends on several factors including clay content, elastomer type, location of clay in blend, and crystallinity of the matrix and elastomer in the presence of MMT. No clear understanding about this behavior is available perhaps the low impact strength arises from the high aspect ratio of clay particles in the polyamide matrix that reduces their ability to contribute to toughening. 

Up to now, the study about phase-separation theory is mainly focused on amorphous/amorphous polymer blend and crystalline/amorphous polymer blend models. There is still lack of systemically theoretical guidance and support for crystalline/crystalline polymer blend models. Therefore, the establishment of the phase-separation theory... 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

FIGURE 6.3 The crystallinity and composition continuum for ethylene- and propylene-dominated polyolefins. Note the dispersion for the propylene-dominated polyolefins due to much-greater prevalence of blends and the presence of tacticity derived changes in crystallinity. 

Blends of enzymatically synthesized poly(bisphenol-A) and poly(p-r-butylphenol) with poly(e-CL) were examined. FT-IR analysis showed the expected strong intermolecular hydrogen-bonding interaction between the phenolic polymer with poly(e-CL). A single 7 was observed for the blend, and the value increased as a function of the polymer content, indicating their good miscibility in the amorphous state. In the blend of enzymatically synthesized poly(4,4 -oxybisphenol) with poly(e-CL), both polymers were miscible in the amorphous phase also. The crystallinity of poly(e-CL) decreased by poly(4,4 -oxybisphenol). 

Aliphatic polyesters based on monomers other than a-hydroxyalkanoic acids have also been developed and evaluated as drug delivery matrices. These include the polyhydroxybutyrate and polyhydroxy valerate homo- and copolymers developed by Imperial Chemical Industries (ICI) from a fermentation process and the polycaprolactones extensively studied by Pitt and Schindler (14,15). The homopolymers in these series of aliphatic polyesters are hydrophobic and crystalline in structure. Because of these properties, these polyesters normally have long degradation times in vivo of 1-2 years. However, the use of copolymers and in the case of polycaprolactone even polymer blends have led to materials with useful degradation times as a result of changes in the crystallinity and hydrophobicity of these polymers. An even larger family of polymers based upon hydroxyaliphatic acids has recently been prepared by bacteria fermentation processes, and it is anticipated that some of these materials may be evaluated for drug delivery as soon as they become commercially available. 

The main limitation of birefringence is that it only provides an averaged orientation value without any discrimination between amorphous and crystalline phases, or between the components in polymer blends, copolymers, and... 

In a classic study that illustrates the principles of the method, an XRPD procedure was described for the estimation of the degree of crystallinity in digoxin samples [35]. Crystalline product was obtained commercially, and the amorphous phase was obtained through ballmilling of this substance. Calibration mixtures were prepared as a variety of blends from the 100% crystalline and 0% crystalline materials, and acceptable linearity and precision was obtained in the calibration curve of XRPD intensity vs. actual crystallinity. Figure 7.13 shows the powder pattern of an approximately 40% crystalline material, illustrating how these workers separated out the scattering contributions from the amorphous and crystalline phases. 

ET40)/PET blends, and in the 100/0 wt% P(HB80-ET20)/PET blend. This is because of either (a) a high content of rigid rod-like liquid crystalline component, or (b) an enthalpy which was too small to detect. The dependence of Tg on the blend composition can be evaluated by using the Gordon-Taylor Equation [37],... 

It is the intent of this doeument to define the terms most commonly encountered in the field of polymer blends and eomposites. The scope has been limited to mixtures in which the eomponents differ in ehemical composition or molar mass or both and in which the continuous phase is polymeric. Many of the materials described by the term multiphase are two-phase systems that may show a multitude of finely dispersed phase domains. Hence, incidental thermodynamic descriptions are mainly limited to binary mixtures, although they can be and, in the scientific literature, have been generalized to multicomponent mixtures. Crystalline polymers and liquid-crystal polymers have been considered in other documents [1,2] and are not discussed here. 

Eoams were extruded from low density polyethylene (LDPE) and blends of LDPE with syndiotactic polypropylene (sPP), using isobutane as the blowing agent. The extruded materials were characterised by measurement of dimensional stability at room temperature, density, tensile properties, dynamic stiffness, and crystallinity determined by differential scanning calorimetry. The sPP, with a slow crystallisation rate, did not interfere with the expansion of the LDPE, and enhanced the temperature resistance by in-situ crystallisation. The blends were flexible, dimensionally... 

The value of the modulus and the shape of the modulus curve allow deductions concerning not only the state of aggregation but also the structure of polymers. Thus, by means of torsion-oscillation measurements, one can determine the proportions of amorphous and crystalline regions, crosslinking and chemical non-uniformity, and can distinguish random copolymers from block copolymers. This procedure is also very suitable for the investigation of plasticized or filled polymers, as well as for the characterization of mixtures of different polymers (polymer blends). 

Cheng SZD, Janimak JJ, Rodriguez J (1995) Crystalline Structures of polypropylene homo- and copolymers. In Karger-Kocsis J (ed) Polypropylene structure, blends and composites, vol 1. Chapman 8c Hall, London, p 33... 

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... 

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