Crystallinity of polypropylene

Crystallinity of polypropylene is usually determined by x-ray diffraction (21). Isotactic polymer consists of heHcal molecules, with three monomer units pet chain unit, resulting in a spacing between units of identical conformation of 0.65 nm (Fig. 2a). These molecules interact with others, or different... 

The crystallization peak temperature increased when epoxy resin was added to polypropylene, that is, the uncured and cured epoxy particles acted as effective nucleating agents and accelerated the crystallization of PP in the blends. When cured dynamically, the smaller epoxy particles in the blends resulted in the increase in the number of nucleating agents and hence accelerated the crystallization of polypropylene. Blending polypropylene with epoxy resin resulted in the decrease of crystallinity of polypropylene and increased the melting temperature T of polypropylene than those of pure polypropylene. 

Studies on Ugnocellulosic material modification were also cmiducted by Nekkaa et al. [18]. The cellulose fibers obtained from Spanish broom (Spartium junceum) were subjected to silane s action to improve adhesion between composite components. Thermal analysis confirmed the nucleating effect uprm the addition of unmodified fibers, while the addition of modified fibers did not significantly influence the crystallinity of polypropylene matrix. 

In this study we showed initial results on the mechanical properties, glass transition temperature and crystallinity of polypropylene+PIB-grafted fumed silica composites. We found that PIB oligomers of different molecular weight on silica have distinct properties in PP. 

Thermodynamic Properties. The thermodynamic melting point for pure crystalline isotactic polypropylene obtained by the extrapolation of melting data for isothermally crystallized polymer is 185°C (35). Under normal thermal analysis conditions, commercial homopolymers have melting points in the range of 160—165°C. The heat of fusion of isotactic polypropylene has been reported as 88 J/g (21 cal/g) (36). The value of 165 18 J/g has been reported for a 100% crystalline sample (37). Heats of crystallization have been determined to be in the range of 87—92 J/g (38). 

The regular syndiotactic and isotactic structures are capable of crystallisation whereas the atactic polymer carmot normally do so. In the case of polypropylene the isotactic material is a crystalline fibre-forming material. It is also an important thermoplastic which can withstand boiling water for prolonged periods. Atactic polypropylene is a dead amorphous material. Polystyrene as commonly encountered is atactic and glass-like but the syndiotactic material... 

Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fiber dimensions. In the second stage, these blends were processed both below and above the Tm of the LCP by extrusion and injection molding. 

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. 

Thin polymer films may also be investigated by TEM and high resolution images are obtained for e.g. thin films of liquid crystalline polymers [64]. Usually thin microtome cuts from bulk samples are investigated, but also epitaxial growth of polyoxymethylene on NaCl [152], chain folding of polyethylene crystals [153], epitaxial crystallization of polypropylene on polystyrene [154] or monomolecular polystyrene particles [155] are observed. The resolution is, however, in most cases not comparable to STM. 

Plastomer, a nomenclature constructed from the synthesis of the words plastic and elastomer, illustrates a family of polymers, which are softer (lower hexural modulus) than the common engineering thermoplastics such as polyamides (PA), polypropylenes (PP), or polystyrenes (PS). The common, current usage of this term is reshicted by two limitahons. First, plastomers are polyolehns where the inherent crystallinity of a homopolymer of the predominant incorporated monomer (polyethylene or isotactic polypropylene [iPP]) is reduced by the incorporahon of a minority of another monomer (e.g., octene in the case of polyethylene, ethylene for iPP), which leads to amorphous segments along the polymer chain. The minor commoner is selected to distort... 

Why does the addition of 5% ethylene into an isotactic polypropylene drastically reduce the crystallinity of the polypropylene relative to the isotactic homopolyer ... 

Figure 19.3 Crosshatched microstructure of alpha crystalline isotactrc polypropylene...

Figure 19.4 Parallel stacks of lamellae in beta crystalline isotactlc polypropylene... 

How does the type and level of tacticity of the polypropylene chain affect the degree of crystallinity of the solid polymer ... 

Which crystalline form of polypropylene exhibits the lowest free energy of crystallization Which form exhibits the highest ... 

The mass fraction crystallinity of molded PHB samples is typically around 60%. As shown in Table 3, PHB resembles isotactic polypropylene (iPP) with respect to melting temperature (175-180°C), Young s modulus (3.5-4 GPa) and the tensile strength (40 MPa). In addition, the crystallinity of iPP is approximately 65% [18]. Accordingly, the fracture behavior of PHB may be anticipated to be tough at room temperature. Molded PHB samples do indeed show ductile behavior, but over a period of several days at ambient conditions, they slowly become more brittle [82, 85, 86]. Consequently, the elongation to break of the ultimate PHB (3-8%) is markedly lower than that of iPP (400%). 

The isotactic polypropylene is an essentially linear, highly crystalline polymer. The density of polypropylene is 0.905. It has high tensile strength, stiffness and hardness due to its high crystalline character. 

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