Polymer blends stiffness

The wall-PRISM theory has also been implemented for binary polymer blends. For blends of stiff and flexible chains the theory predicts that the stiffer chains are found preferentially in the immediate vicinity of the surface [60]. This prediction is in agreement with computer simulations for the same system [59,60]. For blends of linear and star polymers [101] the theory predicts that the linear polymers are in excess in the immediate vicinity of the surface, but the star polymers are in excess at other distances. Therefore, if one looks at the integral of the difference between the density profiles of the two components, the star polymers segregate to the surface in an integrated sense, from purely entropic effects. 

Fig. 46. Normal force (topography) images (a,b) and SLAM amplitude (stiffness) images (c,d) of a PVC/PB polymer blend at room temperature (a,b) and at 373 K (c,d). At high temperature, the matrix became more compliant (darker in the SLAM image). Reproduced from [ 138]...

In most cases the main effect of particles is an increase in stiffness, up to two or three times its original value. In the same way as with polymer blends, this increase in stiffness can be calculated theoretically, namely with the same Kemer formula as in 9.1.6. 

Intermittent contact mode phase imaging is, similar to force modulation and pulsed, force mode, sensitive to differences in materials properties. In Fig. 3.67 (a), the stiffness difference between glass and a polymer-based matrix gives rise to excellent image contrast. In addition, the different components of the polymer blend can be recognized (compare schematic in Fig. 3.67 (b)). 

Enhancement of mechanical properties is of interest only if it is not accompanied by a loss of other important properties of the blend. Of particular concern for such polymer blends is stiffness, because most means of increasing impact strength also reduce stiffness (14-19). But this is not the case for the iPS-fc-iPP-iPS-iPP blends studied here as seen in Table II. It is clear that the enhancement in toughness just described is not accompanied by a loss of stiffness, but it is essentially unaffected by the compatibilizer. And the stiffness of iPS-fc-iPP-iPS-iPP is higher than that of iPP and HIPS. The impact-modulus behavior seems to be due to the tough (or rigid) characteristics, morphologies of phases, and semicrystalline isotactic structure of each block in the iPS-b-iPP diblock copolymer. 

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Most of the polymer blends, grafts, and blocks examined in the preceding chapters formed two amorphous phases. When one phase was plastic and stiff, and the other rubbery and soft, we observed that toughened materials resulted. In this chapter we examine several types of block copolymers in which one or both components crystallize in particular we consider three possible combinations of such blocks ... 

A blend is merely a physical mixture (no chemical bonding) of two or more phases with different chemical compositions as opposed to the copolymer where the constituent phases are actuallyjoined together by chemical bonds [7,206]. In more refined scientific sense, a polymer blend represent a class of materials [analogous to metal (stiff material)-based alloys], in which at... 

Polymer compounding plays an important role in the successful use of polymers. It helps to extend the properties of polymers such as durability, stiffness or thermal resistance so that these properties can be incorporated into an improved end-product. Several thousand of compounds currently used incorporate additives such as antioxidants, fillers or lubricants. Innovation is an essential element in polymer compounding with respect to the manufacture of increasingly sophisticated products such as polymer blends and composites. This book gives an idea of the productive area of polymer compounding. 

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