Self-crosslinking Blends

Ghosh S, Rasmusson J, Inganas O. Supramolecular self-assembly for enhanced conductivity in conjugated polymer blends. Ionic crosslinking in blends of poly(3,4-ethylenedioxythio-phene)-poly(styrene sulfonate) and poly(vinylpyrrohdone). Adv Mater 1998 10 1097-1099. 

Fig. 47 Rheographs obtained from self-crosslinkable CR/XNBR blends of different composition at 180°C. Arrows indicate the development of torque after addition of 10 phr organoclay...

Fig. 49 Physical properties in terms of tensile strength (top) and 50% modulus (bottom) for CR-XNBR blends obtained from self-crosslinking and sulfur-crosslinking processes...

Fig. 50 WAXD patterns of CR and XNBR and their blends obtained from self-crosslinking top) and sulfur crosslinking bottom) processes...

Table II Glass transition temperature of self-crosslinked CR/XNBR rubber blends...

Fig. 52 Tan <5 versus temperature plots of CR-XNBR blends vulcanized by sulfur (top). Storage modulus versus temperature plots of self-crosslinked CR-XNBR blends (bottom)...

The micrographs obtained from scanning electron microscopy are shown in Fig. 54 for the tensile fractured surface of 50 CR/50 XNBR self-crosslinked blend filled with 10 phr layered silicate (Fig. 54a) and for the same blend without any... 

The IR spectra of a self-crosslinked blend of CSM/XNBR [125] following the reaction scheme (Scheme 3.3b) are presented in Figure 3.6. 

Figure 3.6 FTIR-ATR spectra of (a) uncrosslinked 50/50 (w/w) CSM/XNBR blend, (b) self-crosslinked 50/50 (w/w) CSM/XNBR blend, (c) (b-a) difference spectrum...

It is concluded that IR spectroscopy provides information on qualitative as well quantitative analyses of rubbery materials, apart from their microstructures (that is, whether cis or trans, syndiotactic, atactic or isotactic). Different types of rubber blends (compatibilised or self-crosslinked) can be identified by the infrared spectroscopy. Synthesis, and degradation of polymers can also be followed by IR spectra. Mechanism of interaction between rubbers and fillers, can also be studied by IR-spectra. Different types of chemical reactions like the milling behaviour of rubbers, mechanism of adhesion and degradation can also be studied with the help of IR spectroscopy. The technique plays a great role in the product analysis under reverse engineering. 

Raman and IR spectroscopic studies dealing with the qualitative and/or quantitative determination of rubber compounding ingredients, i.e., the elastomer itself [22, 26-31], fillers [32, 33], vulcanisation chemicals and other additives [34-37], are not included here. The same applies to studies dealing with the crosslinking of elastomers by means of chemicals other than sulfur or peroxide [38-41], self-crosslinking of elastomers blends [42-44], crystallisation (strain-induced) [45-48] and oxidation/ageing [49-53]. 

The KAURIT types are either free or etherified N-methylol compounds of urea or of melamine. They are used mainly for the resin finishing of regenerated cellulose fibres, alone and in blends with synthetics. The term "self-crosslinking agents" characterizes their mode of reaction. 

Roychoudhury et al. showed that the double peak of a blend of ENR-50 with chlorosulphonated polyethylene (CSM) at 1 1 weight ratio was changed to a single one (at 2.7 °C) when carboxylated nitrile rubber (XNBR) was added in the stock at 50 wt% (i.e. ENR-50/CSM/XNBR 25/25/50). Additionally, an exothermic peak was detected at 205 °C during a differential thermal analysis of a 33.3/33.3/33.3 mixture of this ternary blend. Taking into consideration that CSM, XNBR and ENR are soluble in chloroform whereas their blend is insoluble, the exothermic peak was attributed to self-crosslinking behaviour of this ternary compound (in the absence of curatives). 

As far as the storage modulus of the self-crosslinked blends is concerned, a relaxation at 40 °C is observed in all the blends (Fig. 30). This relaxation arises due to melting of crystalline domains of the CR chains, and the effect is more prominent in blends of higher CR content without any filler. In the presence of organoclay, crystalline nature of the CR phase is reduced. It will be also interesting to discuss the damping behavior of those composites that are crosslinked by sulfur curatives. 

Curing Agents. Although SBR latexes often do not require use of curing agents in the normal sense, a number of cure systems are available. For noncarboxylated latex compositions, conventional sulfur systems may be used where external heat can be applied. Otherwise phenolic cures may be used or self crosslinking resins may be blended into the formulation. 

The FR characteristics of PCP and Anorin-38 were improved substantially by introducing bromine. When five bronine atoms were introduced by controlled bromi-nation, the resin (the product obtained was still fluid in nature and could be crosslinked by hexamine to get hard partially brominated PCP-PBPCP) showed excellent FR characteristics exhibiting self-extinguishing property and UL 94 V-0 grade when blended with polyethylene, NR, etc. There was excellent compatibility with polyolefins as well as with other polymers such as cellulose, polyurethane, etc. Table 13 shows the FR properties of NR-PBPCP. 

Honomer Selection. In practice the amide/blocked aldehyde precursor 1 (ADDA) proved more readily accessible than 2. The two forms were completely Interconvertible and equally useful as self-and substrate reactive crosslinkers (6). In our addition polymer systems, the acrylamide derivative 1 (R=CH3) provided a good blend of accessibility, physical properties, and ready copolymerizablllty with most commercially Important monomers. Structure/property relationships for other related monomers will be reported elsewhere. 

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