Peroxide reactive extrusion

Wing, R. E., and Willett, J.L. (1997) Water Soluble Oxidized Starches by Peroxide Reactive Extrusion, Ind. Crop. Prod. 1, 45-52. 

Wing RE, Willett JL. 1997. Water soluble oxidized starches by peroxide reactive extrusion. Ind Crops Prod 7 45-52. 

The reactive extrusion of polypropylene-natural rubber blends in the presence of a peroxide (1,3-bis(/-butyl per-oxy benzene) and a coagent (trimethylol propane triacrylate) was reported by Yoon et al. [64]. The effect of the concentration of the peroxide and the coagent was evaiuated in terms of thermal, morphological, melt, and mechanical properties. The low shear viscosity of the blends increased with the increase in peroxide content initially, and beyond 0.02 phr the viscosity decreased with peroxide content (Fig. 9). The melt viscosity increased with coagent concentration at a fixed peroxide content. The morphology of the samples indicated a decrease in domain size of the dispersed NR phase with a lower content of the peroxide, while at a higher content the domain size increases. The reduction in domain size... 

Radical induced grafting may be carried out in solution, in the melt phase,292 29 or as a solid state process.296 This section will focus on melt phase grafting to polyolefin substrates but many of the considerations are generic. The direct grafting of monomers onto polymers, in particular polyolefins, in the melt phase by reactive extrusion has been widely studied. Most recently, the subject has been reviewed by Moad1 9 and by Russell.292 More details on reactive extrusion as a technique can be found in volumes edited by Xanthos," A1 Malaika and Baker et a 21 7 The process most often involves combining a frcc-radical initiator (most commonly a peroxide) and a monomer or macromonomer with the polyolefin as they are conveyed through the extruder. Monomers commonly used in this context include MAII (Section 7.6.4.1), maleimidc derivatives and malcate esters (Section 7.6.4.2), (meth)acrylic acid and (meth)acrylate esters (Section 7.6.43), S, AMS and derivatives (Section 7.6.4.4), vinylsilancs (Section 7.6.4.5) and vinyl oxazolines (Section 7.6.4.6). 

Reactive extrusion is the chemical modification of polymer while it is being transported in an extruder. In this work, polypropylene is intentionally degraded by the addition of a free radical initiator (a peroxide) during extrusion. The product has improved flow properties because of the removal of the high molecular weight tail and the narrowing of the molecular weight distribution. 

The dynamic cross-linking process is used to produce thermoplastic elastomers from mixtures of crystallizable polyolefins and various rubbers. Variations of basically the same method are employed to produce novel, stable polymer alloys by performing chemical reactions during extrusion of such mixtures. In that case, the cunent industrial term is reactive extrusion. Such processes are used, for example, to improve processability of LLDPE s into tubular film (by introducing long chain branches during extrusion with low levels of peroxides) or to... 

A comfortable pathway for improvement of the crystallization of poly(3-hydroxybutyrate) in a melt-spinning process is the use of nucleating agents like electron-beam irradiated PHB [28] or the reactive extrusion with peroxide [29]. 

The addition of peroxides, R OOR", during reactive processing has become a routine aspect of reactive extrusion technology for polypropylene and polyethylene (Xanthos, 1992). In particular, the dialkyl peroxides at a level ranging Ifom 0.001 to 1 wt.% have been used and have half-lives ranging Ifom 1 to 3 minutes at 180 C, so 99% consumption will occur in 7-20 minutes at that temperature. The reaction steps depend on whether oxygen is present... 

In principle, the CL from polyolefins could be used as a monitor of the extent of oxidation during reactive extrusion in the presence of peroxides to decrease the molar mass (Brown, 1992), but this has not been reported. Attention has been paid to the effect that change in viscosity of a polymerizing network has on the CL profile, as described in the following section. 

Common peroxide degradants and stabilizers used in controlled-rheology reactive extrusion are shown in Table 17.2 and 17.8 of Fink (2005). 

Reactive extrusion of PO blends CORl Peroxide modification Kim,1996... 

Standard grade ABS (20% PBD) could also be directiy modified by grafting an anhydride functionality via reactive extrusion with maleic anhydride in the presence of a trace amount of peroxide initiator [Akkapeddi et al., 1990]. Such an extruder maleated ABS upon subsequent melt blending with an amine terminated PA-6, gave a compatibilized ABS/PA-6 blend with significantly... 

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]. 

The compatibilization of TPS and PLA has also been achieved in a one one-step process described by Wang et al. Dicumyl peroxide and maleic anhydride (MA) were used. The process was conducted in a single-screw extruder by one-step reactive extrusion [72]. 

Takamura et al. [127] cross-linked PLLA using various types of peroxides under constant mole ratios of peroxide-derived radicals to PLLA during reactive extrusion in a single-screw extruder (D = 20 mm, L/D = 25) with a fixed temperature profile for the extruder (Zone 1/Zone 2/Zone 3/Die = 180 =C/185°C/190°C/190°C). 

Maliger et al. [216] have reported on a compatible blend of starch and polyester through reactive extrusion using maleic anhydride (MA) and dicumyl peroxide (DCP) as compatilizer and initiator, respectively. It was found that distributing diisocyanate in the polyester phase prior to blending resulted in better mechanical properties than distribution in starch phase [194, 196]. 

Wei and co-workers [38] grafted P(3HB) onto cellulose by the radical initiation of dicumyl peroxide with in situ reactive extrusion. The findings revealed that the reaction time and concentration of dicumyl peroxide significantly influenced the grafting efficiency. SEM confirmed the presence of the grafting reaction between the surface of the cellulose and PHB. DSC analysis showed a reduction of the crystallinity of the graft polymer. TGA analysis further showed that the graft polymer is more thermally stable than P(3HB). 

Reactive Extrusion. Reactive extrusion for grafting poly(/3-hy-droxybutyrate-co-valerate) has been used. Other polymers suitable for grafting are poly(butylene succinate) (PBSU) or poly(caprolacto-ne) (PCL) (18). The grafting of 2-hydroxyethyl methacrylate with a peroxide is shown in Figure 4.1. 1,1,4,4-Tetramethyltetramethylene bis(ferf-butyl peroxide) (Lupersol 101)is a preferred peroxide (18). 

In general, reactive extrusion is the term applied to chemical modification of polymers in the presence of an initiator such as peroxides. During chemical modification, there can be other undesired side reactions taking place, for example, cross-linking, degradation into low MW fractions and so on. Good process control is an essential requisite for attaining a balance of desired properties. 

Another type of reactive extrusion is controlled degradation of PP in the presence of a peroxide initiator to give controlled rheology grade product for film applications. Typical examples of grafting reactions are ... 

BJ Kim, JL White. Thermal/peroxide induced degradation and maleation of polypropylene by reactive extrusion. Int Polym Proc 10(3) 213-220, 1995. 

Initiation or chain start when an initiator (in reactive extrusion generally a peroxide) decomposes and initiates a radical on a monomer molecule. 

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