Two-step reactive blending

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]...

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]. 

Reactive dyes are well suited to dye blends of cellulose and PA fibers. Clear shades with very good fastness are obtained. Like with vat dyes, the depth of shade of reactive dyes depends relatively strongly on the type of PA and structural differences. Dyeing is carried out in a three-step process with appropriately selected products. First, the reactive dyes in a weakly acidic liquor are allowed to absorb on the PA component. Salt is then added to improve the yield on the cellulose component. Finally, the liquor is made alkaline for reaction with the cellulose fiber. Dyes (e.g., with MTC anchor) that dye PA from a neutral liquor in the presence of salt are applied in a two-step process, as in the case of cellulose. In the reversal of this dyeing process, the cellulose component is dyed first at alkaline pH, followed by neutralization with acid, and the PA component is then covered at elevated temperature. 

To toughen PA, 2-5 wt% of either PO, elastomer, ionomer, acidified or epoxidized copolymer may be added. PA/PO blends of type (2) were developed to improve dimensional stability and to reduce water absorbency of PA. Alloying PA with PO reduces the rate of water migration to and from the blend, but not the inherent water absorption of PA [Utracki and Sammut, 1991, 1992]. The alloying is either a two- or three-step reactive process (1°) acidification of PO, (2°) preparation of a compatibilizer, and (3°) compounding PP, PA, and the compatibilizer. Usually, the reactive blending is carried out in a twin screw extruder [Nishio et al., 1990 Hu and Cartier, 1998], Since it may cause reduction of the blend crystallinity (thus performance), the extend must be optimized. The rigid PA/PP blends usually comprise PA PP =... 

PP was maleated then reactively blended with PA to obtain 12 wt% of PP-co-PA two-step blending maleation of PP, incorporation of PA Glotin etal.., 1989... 

A surfactant-free method for the preparation of exfoliated EVA/silicate nanocomposites has been developed recently by Sogah et al. [90,91]. The process comprises two steps the first step involves the reactive solution blending of MMT-Na+ (with a CEC 0.90 mequiv. g ) with preformed random copolymers of VA and 2-(acryloyloxy)ethyltrimethyl ammonium chloride (AETMC) the second step, also made by solution blending, consists of a dilution with EVA of the masterbatch prepared in the first step. As AETMC is more reactive than... 

This chapter present a state-of-the-art review of the field with examples that are presented in two parts. Part I is focused on polymerization reactions by chain addition and step growth mechanisms, while Part II describes reactive modifications of polymers via side group modifications, reactive blending, or depolymerizations reactions. Future directions and research needs are also presented. 

The conceptual breakdown in Fig. 1.9 (27) simply indicates the fact that in compounding, blending, and reactive processing, the base polymer(s) undergo two thermomechanical elementary-step experiences, and that the product of the first are value-added and microstructured pellets, while the second is used primarily for fabricating finished products. The important elementary steps for each experience, and the physical mechanisms that affect them, are different, because of the different objectives in each. 

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. 

Of the various compatibilization strategies that have been devised, an increasingly common method is either to add a block, graft, or crosslinked copolymer of the two (or more) separate polymers in the blend, or to form such copolymers through covalent or ionic bond formation in situ during the Reactive Compatibilization step. The first of these processes was described in Chapter 4 of this Handbook, Interphase and Compatibilization by Addition of a Compatibilizer, while the second method is the topic of this Chapter. 

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