Stiffness enhancement

Clearly there are many permutations of D,b,h,a, etc and Fig. 2.31 shows how the stiffness enhancement factor, q, changes with various values of these parameters. In each case the angle a has been fixed at 85° and the corrugation dimensions have been expressed as a function of the wall thickness, h. 

Short Chopped Fibres These are fibres with lengths up to about 6 mm. The fibre (L/D) ratio is typically about 800. They are more expensive than milled fibres but provide better strength and stiffness enhancement. 

Thus, Hope and his coworkers concluded for the solid-state extrusion of linear poly-ethylenes that increasing the molecular wei t reduced both the maximum degree of deformation and the tensile properties of the jaoduct. Hie sother hand, increased the maximum degree of deformation. The degree of stiffness enhancement upon extrusion and the melting points of the products were reduced. 

Finally, creative combinations of low-cost fillers in various forms allow reduced resin content without reducing desired properties. Blends of small and large particles of the same filler material, or blends of plate-like filler particles and coarse filler, help limit the filler s most extreme, unwanted effects on stiffness, strength, or impact behavior. For example, platy talc, mica, or kaolin day in a PO provides stiffness enhancement, which complements the strength properties provided by fiber-shaped wollastonite or the more forgiving impact properties of spherical caldum carbonate partides [7-6]. 

Nucleation. Nucleating offers an interesting way of PP modification and a high munber of PP-grades modified in such a way is offered by most PP manufacturers. The main reason for nucleation is to obtain high clarity, but also the improvement of the mechanical properties (especially stiffness enhancement) and the reduction of cycle time are of paramount interest. 

As it is well-known [26], very often a filler introduction in polymer matrix is carried out for the last stiffness enhancement. Therefore, the reinforcement degree of polymer composites, defined as a composite and matrix polymer elasticity moduli ratio, is one of their most important characteristics. 

Figure 15.11. Variation of stiffness enhancement with changing aspect ratio, for randomly orientated straight platelets, with a fixed area filling fraction of 4%...

Figure 15.19. The variation in stiffness enhancement with the number of layers in the stack, at various area filling fractions, where all the particles are aligned with the -direction...

Although polymer nanocomposites display a stiffness enhancement that as with more conventional composites tends to be linear with increasing filler volume fraction, this may not be fully linear and may also more conventionally exhibit a critical volume fraction, beyond which stiffness starts to decrease due to nanofiller accumulation and thus efficiency loss [26],... 

Y. C. Gu et al.[2] used the POE as the toughness modifier and clay as the stiffness enhancer to study their effects on the toughness of PP. Results showed that blends of clay and POE could increase the toughness of PP. R. H. McGirk and M. M. Hughes[3] have used POE to improve the toughness of clarified PP which is weak on impact performance. 

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