Polyolefin mechanical performance

Different ternary blends were prepared by mixing iPP with several polyolefins with the aim to modify the mechanical properties of the matrix (25-29). The effect of the composition on the morphology, the rheological properties, and the crystallization behavior was investigated. The nature of the components can act as a nucleant agent on iPP crystallization and can produce different effects on mechanical performance of the blends. 

The major drawback of cellulose fibers in the present context resides in their highly polar and hydrophilic character, which make them both poorly compatible with commonly used non-polar matrices, such as polyolefins, and subject to loss of mechanical properties upon atmospheric moisture absorption. That is why they should be submitted to specific surface modifications in order to obtain an efficient hydrophobic barrier and to minimize their interfacial energy with the often nonpolar polymer matrix, and thus generate optimum adhesion. Further improvement of this interfacial strength, which is a basic requirement for the optimized mechanical performance of any composite, is attained by chain entanglement between the matrix macromolecules and the long chains appended to the fiber surface (brushes) or, better still, by the establishment of a continuity of covalent bonds at the interface between the two components of the composite. 

Wood fiour is often added to thermoplastics as a low cost filler to alter mechanical performance, especially the stiffness of low melt temperature, commodity thermoplastics such as polypropylene and polyethylene without increasing density excessively. Wood is much stiffer than the commodity thermoplastics usually used as matrices. Additionally, vood and pulp fibers can nucleate crystal growth in polyolefins resulting in a transcrystalline layer that can infiuence mechanical behavior [33, 34[. 

Because gelled or networked polyolefins are almost completely infusible and insoluble, even small amounts can adversely affect the appearance and mechanical performance of a fabricated article. 

PHA for biocomposite elaboration is its polar character. PHA shows better adhesion to ligno-cellulose fibres compared to conventional polyolefins. We can find a lot of papers based on PHA-biocomposites. The addition of cellulose fibres and different fillers has often been proposed as a solution to increase the mechanical performance and toughness of PHB and PHBV. ... 

In recent years, there has been a growing use of polypropylene materials in laundry appliances. Advances in mechanical performance and corrosion resistance have increasingly enabled advanced polyolefins to replace stainless steel in appliances, providing significant advantages in terms of material costs, manufacturing processes, and overall product design. 

Asahi Chemical Industry carried out an exploratory investigation to determine the requirements for cellulose based separators for lithium-ion batteries. In an attempt to obtain an acceptable balance of lithium-ion conductivity, mechanical strength, and resistance to pinhole formation, they fabricated a composite separator (39—85 /cellulosic fibers (diameter 0.5—5.0 /pore diameter 10—200 nm) film. The fibers can reduce the possibility of separator meltdown under exposure to heat generated by overcharging or internal short-circuiting. The resistance of these films was equal to or lower than the conventional polyolefin-based microporous separators. The long-term cycling performance was also very comparable. 

The ability to modify their structure and the good cost/ performance ratio makes polyolefins technically and commercially attractive for mechanical energy absorption. This is especially true for High Melt Strength (HMS) PP which allows continuous extrusion foaming. Physical expansion of PP, properties of foamed PP, and application examples are considered in detail, mechanical properties in particular being compared with other polymer foams. 

As discussed in the first part, blends containing immiscible components such as polyolefins could improve the performances of the inherently brittle sPS. Until now the reported investigations have concerned simple binary blends containing a polyolefin and sometimes SEBS as a compatibilizer. In addition, sPS/ polyurethane and sPS/sulfonated sPS blends were also investigated. All these studies tried to correlate the microscopic features of the blends with their mechanical properties. 

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