One-step reactive blending

Figure 6.20 Three different one-step reactive blending processes for the PP/PA6 (80/20) blend. Bl (functionalization + reactive compatibilization) -I- devolatilization B2 functionalization -I- reactive compatibilization -I- devolatilization B3 functionalization -I- devolatilization + reactive compatibilization. After Cartier and Hu [44]...

Figure 6.25 Comparison between an optimized one-step reactive blending process and a classical two-step reactive blending process for die PP/PBT (70/30) blend. After Sun et al. [52]...

Shujum et al. described compatible TPS/LLDPE blends, produced by one-step reactive extrusion in a single-screw extruder. Maleic anhydride (MAH), and dicumyl peroxide (DCP) were used to graft MA onto the LLDPE chain [88]. 

Recently, Wang et al. [16] reported preparation of PLA/starch blends by one-step reactive extrusion. In the presence of dicumyl peroxide, the compatibility of thermoplastic dry starch (DTPS)/PLA blends, using MA as compa-... 

In this way, the functionalization of one component in immiscible polymer blends has attracted great interest in terms of the compatibilization.For example, Lambla and his coworkers reported a series of works on the in situ compatibilization of immiscible polymer blends by one-step reactive extm-sion. ° They described the chemical reactions related to compatibiUzing polymer blends, especially for the PBT/polypropylene (PP) blend system. They stressed that the monomers used for functionalizing PP, such as acrylic acid (ACID), MAH, GMA, and oxazoline, are potentially reactive towards the carboxylic acid and/or hydroxyl groups at the chain ends of the PBT and are melt grafted onto the PP by free-radical reactions. 

The second system was based on two semi-crystalline polymers polypropylene and polyamide. To attain potential reactivity, polypropylene was first grafted with maleic anhydride and the results of this radicalar melt-grafting are presented. The final blend was obtained in one-step extruding of the two homopolymers and the reactive polypropylene. 

The degradation and transesterification steps are carried out in the first part of the reactive extrusimi. The first results regarding the material properties of the blends demonstrate a successful increase of the characteristic values. This one-step process is a very interesting method for the recycling of mixed PET/PA postconsumer waste. 

Figure 6.22 compares the performance of the one-step and two-step reactive compatibilization processes. The one-step process corresponds to screw profile B3. In order to make the comparison meaningful, the two-step process uses the same screw profile as the one-step process. Moreover, the composition of the free radical grafting system is the same for both processes, namely, PP/MA/styrene/peroxide = 100/1.5/1.6/0.3 by weight. In this way, the amount of grafted MA onto PP is the same (0.5 phr) in both processes. Five different PP/PA6 (80/20) blends are made using the two-step process in which the PP phase contains 0,20,40,60 or 80wt.% PP-g-MA. The rest of the PP phase is composed of an inert PP (the inert PP used has better mechanical properties than that used for the experiments in Fig. 6.21). The same number of PP/PA6 (80/20) blends is obtained using the one-step process. In order for the blends obtained with the one-step process to have the same compositions (the inert PP, PP-g-MA and PA6) as those obtained with the two-step proeess, the feed rates at the first and second hoppers for different chemicals are adjusted accordingly. Results show that the compatibilization perfonnance of the one-step process is quite similar to that of the two-step process. For example, none of the blends...

Reactive compatibilization can also be accomplished by co-vulcanization at the interface of the component particles resulting in obliteration of phase boundary. For example, when cA-polybutadiene is blended with SBR (23.5% styrene), the two glass transition temperatures merge into one after vulcanization. Co-vulcanization may take place in two steps, namely generation of a block or graft copolymer during vulcanization at the phase interface and compatibilization of the components by thickening of the interface. However, this can only happen if the temperature of co-vulcanization is above the order-disorder transition and is between the upper and lower critical solution temperature (LCST) of the blend [20]. 

Although the mechanism of copolymerization is similar to that discussed for the polymerization of one reactant (homopolymerization), the reactivities of monomers may differ when more than one is present in the feed, i.e., reaction mixture. Copolymers may be produced by step-reaction or by chain reaction polymerization. It is important to note that if the reactant species are Mi and M2, then the composition of the copolymer is not a physical mixture or blend, though the topic of blends will be dealt with in this chapter. 

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