Fracture polypropylene

Fractured polypropylene labelled with nitroxide radicals were also studied in a... 

The narrow molecular weight distribution means that the melts are more Newtonian (see Section 8.2.5) and therefore have a higher melt viscosity at high shear rates than a more pseudoplastic material of similar molecular dimensions. In turn this may require more powerful extruders. They are also more subject to melt irregularities such as sharkskin and melt fracture. This is one of the factors that has led to current interest in metallocene-polymerised polypropylenes with a bimodal molecular weight distribution. 

The model has also been found to work well in describing the mechanics of the interface between the semicrystalline polymers polyamide 6 and polypropylene coupled by the in-situ formation of a diblock copolymer at the interface. The toughness in this system was found to vary as E- where E was measured after the sample was fractured (see Fig. 8). The model probably applied to this system because the failure occurred by the formation and breakdown of a primary craze in the polypropylene [14],... 

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%). 

Abstract The fracture properties and microdeformation behaviour and their correlation with structure in commercial bulk polyolefins are reviewed. Emphasis is on crack-tip deformation mechanisms and on regimes of direct practical interest, namely slow crack growth in polyethylene and high-speed ductile-brittle transitions in isotactic polypropylene. Recent fracture studies of reaction-bonded interfaces are also briefly considered, these representing promising model systems for the investigation of the relationship between the fundamental mechanisms of crack-tip deformation and fracture and molecular structure. 

Keywords Polyethylene Polypropylene Microdeformation Fracture Slow crack growth... 

Figure 5.25 Scanning electron micrographs of fracture surfaces of polypropylene/wood fibres composites. Left with maleated PP right without MAPP...

The fracture resistance of a homopolymer is controlled by (i) the number of tie-molecules, which act as stress transducers between the crystallites and (ii) by the disentanglement resistance of the individual chains [112-115]. The higher the molecular weight, the more likely both factors are high fi-nucleated polypropylene does not infringe this rule [33,72,74,116]. 

If homolytic scission of polymer main-chain is induced by mechanical fracture, primary mecbano-radical must be formed in a pair. However, for homogeneous polymers, like PE, PTFE and PB, it is hard to demonstrate the pair formation of mechano-radical. Simplest heterogeneous polymer, polypropylene, is probably the best sample for the purpose of experimental verification of pair formation of the mechano-radical. 

Friedrich, K., Karsch, U. A. The Influence of Molecular Weight on Crazing and Fracture in Polypropylene, in Proc. 27th Int. Symp. on Macromolecules, Vol. 2, p. 1035, Strasbourg, France, July 1981... 

In the Multigrain model, fractured catalyst microparticles are produced during the polymerization and uniformly dispersed in the polymer each of these particles behaves as a micro Solid core and diffusion within them, as well as in the interstices between them, can take place. In the Polymeric flow model the catalyst microparticles are dispersed in a polymer continuum and move outward in proportion to the volumetric expansion due to polymerization only one value of diffusivity is considered. Both these models predict significant MWD broadening due to mass transfer limitations (Q , 9 for polypropylene in the Polymeric flow model) on the basis of mathematical calculations carried out assuming reasonable values of the kinetic and physical parameters. 

Polypropylene, fracture toughness, elastic modulus, filler particle, crack resistance, debonding, cavitation, process zone, silica, calcium carbonate. 

The content of amorphous phase and the small size of spherulites lead to an improvement of the fracture toughness of Polypropylene [16]. In presence of mineral filler, the particle surface chemistry can induce some specific microstructural characteristics of the PP matrix parameters such as degree of crystallisation, spherulite size, and p phase content (a/p ratio) [16]. 

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