Compatibilizers selection

M. J. A Chowdhury, and M. P. Wolcott, Compatibilizer selection to improve mechanical and moisture properties of extruded wood-HDPE composites. Forest Products J. 57 (9), 46-53 (2007). 

PBAs are designed explicitly to meet the needs of specific applications on the basis of their property-processing-cost performances. One polymer is incorporated into the matrix of other polymers to impart specific characteristics as per the requirement along with the appropriate compatibilizer to ensure stress transfer in between phases. The polymer blend constituents and composition must, therefore, be selected on the basis of the compensation of properties, considering the advantages and disadvantages associated with each phase. Table 12 indicates some of the components used as modifiers. 

Short block copolymers with well defined number of units in the blocks could be applied as selective absorbents, compatibilizers for polymer blends, components for polymeric membranes, etc. 

Overall, the plasma-treated samples show an improvement in terms of dispersion and tensile properties. Treatment with different plasma monomers show different levels of improvement in terms of dispersion and final vulcanizate properties due to the different levels of compatibilization in the polymer blend and, more specifically, with the different polymers used in this blend. The most important aspect for achieving an optimal balance between the properties of a filled polymer blend for a specific application is the selection of the proper monomer for the plasma modification of the silica surface, in relation to its required compatibility with a particular polymer in the blend. 

The fundamental relationships between compatibilization and selective blending on the blend characteristics and the foaming behavior, as demonstrated in the following, will not only be valid for this particular blend system, but will help to understand and control the foaming behavior of multiphase polymer blends in general. 

The solubility of carbon dioxide at the selected saturation conditions of 5 MPa and 40°C, is shown in Table 1. Both the uncompatibilized and the compatibilized PPE/SAN blends absorb similarly high amounts of carbon dioxide in the range of 100, mgg-1. However, in contrast to one-phase systems, the solubility data of the overall multiphase blend is not sufficient to describe the system, but the content of carbon dioxide in each blend phases needs to be considered. In the case of PPE/SAN blends compatibilized by the SBM triblock terpolymers, one can distinguish three distinct phases, when neglecting interfacial concentration gradients (idealized case) (1) the PPE phase intimately mixed with the PS block, (2) the SAN phase mixed with the PMMA block, and (3) the PB phase located at the interface between PPE/PS and SAN/PMMA. 

In the previous sections the foamability of the PPE/SAN blend systems containing elevated contents of the higher viscosity PPE phase were improved by (1) selective blending with PS as well as (2) compatibilization with SBM. 

Similar to the previously investigated blend systems, selective blending of PPE/SAN with PS allows PPE/PS matrix structures to form in both the noncompatibilized as well as in SBM-compatibilized blend systems (Fig. 31). Already the noncompatibilized (PPE/PS)/SAN blend shows a finely dispersed SAN phase with a particle size in the range of 1 pm (Fig. 31a). The addition of small amounts of SBM to the ternary (PPE/PS)/SAN blend has no significant effect on the particle size of the dispersed SAN phase (Fig. 31b). By further increasing the SBM content to 10 and 20wt%, a remarkable refinement of the SAN phase can be detected (Fig. 31c,d). While the particle size of the SAN phase is reduced to about 500 nm for 10 wt% SBM, SAN particles far below 300 nm can be detected for the high SBM amount of 20 wt%. 

Demonstier-Champagne et al. used atomic force microscopy (AFM) to observe microphase separation within cast films of PS-PMPS-PS/ PS-PMPS block copolymer mixtnre [43] that were nsed to compatibilize a blend of PMPS and PS. The fractnre snrface of blend films with the block copolymer incorporated show a far finer dispersion of particle sizes than those without. Matyjaszewski et al. studied PMPS-PS thin films by SFM (scanning force microscopy) and TEM (transmission electron microscopy) and Fig. 8 shows a TEM picture of a thin section of a film which was prepared by slow evaporation from THE, which is slightly selective for the polystyrene block [73]. 

Block copolymers in selective solvents exhibit a remarkable capacity to self-assemble into a great variety of micellar structures. The final morphology depends on the molecular architecture, tlie block composition, and the affinity of the solvent for the different blocks. The solvophobic blocks constitute the core of the micelles, while the soluble blocks form a soft and deformable corona (Fig. Id). Because of this architecture, micelles are partially Impenetrable, just like colloids, but at the same time inherently soft and deformable like polymers. Most of their properties result from this subtle interplay between colloid-like and polymer-like features. In applications, micelles are used to solubilize in solvents otherwise insoluble compounds, to compatibilize polymer blends, to stabilize colloidal particles, and to control tire rheology of complex fluids in various formulations. A rich literature describes the phase behavior, the structure, the dynamics, and the applications of block-copolymer micelles both in aqueous and organic solvents [65-67],... 

Mechanical Properties. The mechanical properties of the selected blends studied, including the results of tensile, Izod impact, and falling-weight impact tests, are summarized in Table I. Generally, lower-than-expected toughening efficiency (especially for Izod impact) and data scattering were obtained because it is hard to maintain consistent moisture content of the specimens (especially for blends in which PA is the major component). The presence of the compatibilizer in all the blends resulted in consistent and substantial improvement in properties (Nos. 2, 3, and 4 vs No. 1, and No. 20 vs... 

This study demonstrated that the final destination of the added core-shell rubber particles, in PC, PA, or both, in the PC-PA binary blend can be controlled by properly selecting the chemical structure of the shell in the core-shell rubber. The unreactive MBS rubber tends to reside in the PC phase and near the vicinity of the PC-PA interface. The reactive MBS-MA rubber can have a chemical reaction with PA end groups and can therefore be retained within the PA phase. High-molecular-weight bisphenol A epoxy resin has proved to be an efficient compatibilizer for PC-PA blends. Rubber-toughening of the PC-PA blend in which PC is the matrix is much more effective than with blends in which PA is the matrix. 

One possible way of reducing interfacial tension and improving phase adhesion between PP-based blend phases is to use a selected copolymeric additive that has similar components to the blend, as a compatibilizer in the blend system. Well-chosen diblock copolymers, widely used as compatibilizing agents in PP-based blends, usually enhance interfacial interaction between phases of blends (15, 16), reduce the particle dimensions of the dispersed phase (16, 17), and stabilize phase dispersion against coalescence (16-18) through an emulsification effect, thus improving the mechanical properties (15-19). 

Bockstaller MR et al (2003) Size-selective organization of enthalpic compatibilized nanocrystals in ternary block copolymer/particle mixtures. J Am Chem Soc 125(18) 5276-5277... 

Because the individual blocks in a block polymer exhibit selective solution properties, a block polymer may act as a surface active agent. It can be accommodated at an interface between two phases of other materials if it contains blocks compatible with each phase, respectively. Thus, it can act as an emulsifier between two incompatible solvents, or other liquids. In the same way it can act as a compatibilizer or dispersing agent between two incompatible resins or polymers if these resins or polymers are compatible with the respective blocks. 

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