Miscibility rubber blends

The formation of miscible rubber blends slows the rate of crystallization (Runt and Martynowicz, 1985 Keith and Padden, 1964) when one of the components is crystallizable. This phenomenon accounts for data that show lower heats of fusion that correlate to the extent of phase homogeneity (Ghijsels, 1977) in elastomer blends. Additionally, the melting behavior of a polymer can be changed in a miscible blend. The stability of the liquid state by formation of a miscible blend reduces the relative thermal stability of the crystalline state and lowers the equilibrium melting point (Nishi and Wang, 1975 Rim and Runt, 1520). This depression in melting point is small for a miscible blend with only dispersive interactions between the components. 

Miscible blends should have greater mechanical integrity than a comparable multiphase structure. Miscible rubber blends that react chemically have a densiflcation and a higher cohesive energy density. This may provide improved mechanical properties but has been observed only below the Tg (Kleiner et al., 1979). 

Other recent studies which involve and illustrate the power of the FTIR technique include surface studies of PVC systems with PMMA [192] and poly(e-caprolactone) (PCL) [193, 194] PVC with styrene/acrylonitrile copolymers [195] polyester/nitrocellulose [196] EVA copolymer with PVC and chlorinated polyethylene (CPE) [197] and interactions in blends involving p-sulphonated polystyrene [198, 199]. FTIR techniques have been used to map the phase diagram of an aromatic polyamide-poly(ethylene oxide) blend [200], while microscopy-FTIR has been used to obtain information on intermolecular interactions and conformational changes in specific domains in functionalised polyolefins with PVC or polystyrene [201]. Segmental motions and microstructure studies from combined DSC and FTIR measurements have been used to interpret solid-state transitions in miscible rubber blends [202]. 

Krishnamoorti, R. in Miscibility of Blends of Saturated Hydrocarbon Elastomers. Rubber Division, Proceedings of the American Chemical Society, Nashville, TN, Sept. 29-Oct. 2, 1998, Paper No. 33, 1-14. 

Comparisons of the theory with experiment can not be presently made due to the lack of data on well characterized molecular IPN. Indications about its validity can, however, be deduced by examining its consistency at extreme cases of material behavior. The agreement at the one-component limit, for example, provided that the rubber is not very weak (iji not very small), has been successfully demonstrated by Ferry and coworkers [ ]. A useful result is obtained at the version of the theory applicable to the fluid state (i.e., at the limit of zero crosslinking). From the last two terms of Equation 13, the following relationship can be derived for the plateau [ ] and time dependent relaxation modulus of miscible polymer blends ... 

Bhattacharya AK et al. (1995) Studies on miscibility of blends of poly(ethylene-co-methyl acrylate) and poly(dimethyl siloxane) rubber by melt rheology. J Appl Poly Sci 55( 13) 1747—1755... 

A group of new, fully miscible, polymer blends consisting of various styrene-maleic anhydride terpolymers blended with styrene-acrylonitrile copolymer and rubber-modified versions of these materials have been prepared and investigated. In particular the effects of chemical composition of the components on heat resistance and the miscibility behavior of the blends have been elucidated. Toughness and response to elevated temperature air aging are also examined. Appropriate combinations of the components may be melt blended to provide an enhanced balance of heat resistance, chemical resistance, and toughness. 

Even in the phase separated blends, where some degree of partial miscibility or compatibility exists between the components, simple melt blending in an intensive shear mixer is adequate for making a well dispersed, reasonably stable blend product with useful combination of properties, such as polypropylene/ethylene-propyl-ene rubber blend, ABS/polycarbonate blend, etc. The self-compatibUizing nature of these blends stems from partial miscibility and the mutual interpenetration of polymer chains at the interface. Slight modifications of the polymer backbone are often employed, particularly in the case of styrenic and ABS resins to induce partial miscibility with other resins. 

In PVC/nitrile rubber blends, PVC is added more as an ozone resistant additive. In these ther-moplastically processable blends, PVC is flexibil-ized enough to be used for soft goods, wire jacketing, hoses, gaskets and seals. When the NBR contains >25% acrylonitrile, it becomes miscible with PVC and at < 20% acrylonitrile level, it is fairly compatible due to partial miscibility [Matso et al., 1969]. 

In 1979, the UNIPOL process for gas-phase production of LLDPE was introduced by the Union Carbide Corp. Since the new resins were difficult to process on the lines designed for LDPE, by 1982 several patents were issued for improvement of LLDPE processability by blending it with other polyolefins, viz., LDPE, PP, and olefinic rubbers. Ethylene copolymers, rubbers, EPDM, EVAc, maleated polypropylene, EPR, etc., have also been used (Cowan 1983 Turtle 1983 Fukui et al. 1983 Haas 1983 Hert 1983). Thus, blends LLDPE/LDPE were found miscible at low LDPE contents, then immiscible at high LDPE. Addition of HDPE as cosolvent resulted in miscible tertiary blends (Lee and Denn 2000). 

In a typical formulation, an ethylene-n-butylacrylate-carbon monoxide (60/30/ 10) terpolymer (60 wt%) is melt compounded in a twin-screw extmder with PVC (30 wt%) along with an optional, nonvolatile plasticizer such as trioctyl trimellitate (10 wt%) such that the ethylene terpolymer dispersion was cured in situ during the mixing by catalytic amounts of a suitable peroxide (0.3 %) and a bismaleimide crosslink promoter (0.2 %). It is believed that the initial homogeneous miscible melt blend later forms the micro phase-separated mbber domains as the selective rubber cross-Unking progresses. Currently, such TPV blends are commercially sold as Alcryn melt-processable rubbers by Advanced Polymer Alloys division of Ferro. 

In bromobutyl/chlorobutyl rubber blends, both elastomers have the polyisobutylene backbone and halogen reactive functionality. These polymers, being molecularly miscible, constitute an ideal system for co-vulcanization. Bromobutyl and chloro-butyl can be used interchangeably without significant effect on state of cure as measured by extension modulus, tensile strength, and cure rheometer torque development. Bromobutyl will increase the cure rate of a blend with chlorobutyl. However, where bromobutyl is the major part of the blends, chlorobutyl does not reduce scorch tendencies because the more reactive halogen unit can dominate. 

Polymer blends are a mixture of at least two polymers, their combination being supposed to lead to new materials with different properties. The classification of polymer blends into (1) immiscible polymer blends, (2) compatible polymer blends, and (3) miscible polymer blends is given by the thermodynamic properties of the resulting compound by means of the number of glass transition temperatures observed for the final product. To improve the compatibility between the blended polymers, some additives or fillers are used. To the same extent, rubber blends are mixtures of elastomers, which are usually combined to obtain an improved product, with properties derived from each individual component. 

Rubber blending of PP is used to improve its impact properties. Miscibility, however, is exception rather than rule in polymer systems and consequently processing of polymer blends is quite complicated with respect to control of morphology. An induced morphology may be preserved using radiation techniques to crosslink the dispersed phase in polymer blends isotactic-polypropylene/ethylene- propylene (diene... 

Volume 1 of this book is comprised of 25 chapters, and discusses the different types of natural rubber based blends and IPNs. The first seven chapters discuss the general aspects of natural rubber blends like their miscibility, manufacturing methods, production and morphology development. The next ten chapters describe exclusively the properties of natural rubber blends with different polymers like thermoplastic, acrylic plastic, block or graft copolymers, etc. Chapter 18 deals entirely with clay reinforcement in natural rubber blends. Chapters 19 to 23 explain the major techniques used for characterizing various natural rubber based blends. The final two chapters give a brief explanation of life cycle analysis and the application of natural rubber based blends and IPNs. 

The miscibility of natural rubber (NR) blends is one of the most important factors when designing NR products. For instance, when the NR is miscible with a dissimilar polymer on a molecular level, we may improve the properties of NR as a function of the composition of the polymer. This is significantly different from the design for immiscible NR blends, whose properties are greatly dependent upon the morphology of the blend but less so on the composition. In most cases, NR is immiscible with non-polar synthetic rubbers, i.e. NR/butadiene rubber (BR) with high c -1,4-butadiene units, NR/styrene-butadiene rubber (SBR), NR/butyl rubber (IIR), NR/silicone rubber (q)13,i4 NR/ethylene-propylene-diene rubber (EPDM). This means it is important to find miscible NR blends and to control the morphology of the immiscible NR blends in a rational way. In this chapter, properties of NR blends are described from the viewpoint of miscibility, i.e. the miscible blend of NR/BR and the immiscible blend of NR/SBR. 

The thermal properties of NR based polar synthetic rubber blends is expected to affect the application range of these vulcanizates. Degradation, glass transition and crystallization temperatures determine the service conditions of each blend. Additionally, the existence of single or multiple shifted or not glass transition temperatures of each blend supplies evidence for the miscibility of the components involved. " Nevertheless, in many cases further analysis might be required to determine miscibility. 

Natural rubber based-blends and IPNs have been developed to improve the physical and chemical properties of conventional natural rubber for applications in many industrial products. They can provide different materials that express various improved properties by blending with several types of polymer such as thermoplastics, thermosets, synthetic rubbers, and biopolymers, and may also adding some compatibilizers. However, the level of these blends also directly affects their mechanical and viscoelastic properties. The mechanical properties of these polymer blended materials can be determined by several mechanical instruments such as tensile machine and Shore durometer. In addition, the viscoelastic properties can mostly be determined by some thermal analyser such as dynamic mechanical thermal analysis and dynamic mechanical analysis to provide the glass transition temperature values of polymer blends. For most of these natural rubber blends and IPNs, increasing the level of polymer and compatibilizer blends resulted in an increase of the mechanical properties until reached an optimum level, and then their values decreased. On the other hand, the viscoelastic behaviours mainly depended on the intermolecular forces of each material blend that can be used to investigate the miscibility of them. Therefore, the natural rubber blends and IPNs with different components should be specifically investigated in their mechanical and viscoelastic properties to obtain the optimum blended materials for use in several applications. 

Neutron scattering is being used in a wide variety of applications in the study cf polymer structure. These include studies of dimensions of polymer chains in solution, conformation of chains in networks to test theories cf rubber elasticity, miscibility of blends, structure of block copolymws and semicrystalline polymers, and size and shape of bio-macromolecules. Adsorbed polymer layers can be studied by neutron reflectivity. 

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