Free Radical Grafting Of Maleic Anhydride Research Articles

Compatibilization of polypropylene/recycled polyethylene terephthalate blends with maleic anhydride grafted polypropylene in the presence of diallyl phthalate

Bi-functional co-agent, diallyl phthalate (DAP), −assisted melting free-radical grafting of maleic anhydride (MAH) on polypropylene (PP) is carried out by reactive extrusion. The PP/recycled polyethylene terephthalate (rPET) blends with and without PP-g-MAH/DAP (PP grafted with both MAH and DAP) are conducted on a twin-screw extruder. It reveals that the introduction of DAP can significantly enhance the grafting degree of MAH and decrease the chain scission of PP. The maximum extent of MAH grafting (1.5 wt.%) is obtained when DCP and MAH contents are 0.5 and 6.0 wt.%, respectively, and the DAP/MAH molar ratio is 0.3. Besides, differential scanning calorimetry (DSC) analysis shows that the crystallization temperature of grafted PP is higher than that of pure PP due to the nucleation of grafted groups. Fourier transform infrared spectroscopy (FTIR) analysis proves that chemical reactions take place between PP-g-MAH/DAP and rPET. In particular, scanning electron microscopy (SEM) observations demonstrate that, the PP/rPET blends compatibilized with PP-g-MAH/DAP show enhanced adhesion at the interface comparing with the binary PP/rPET blend, which is also proved by DSC measurements, dynamic mechanical analysis (DMA) and mechanical properties.

Melt Free-Radical Grafting of Maleic Anhydride onto Biodegradable Poly(lactic acid) by Using Styrene as A Comonomer

Maleic anhydride (MA) was grafted onto poly(lactic acid) (PLA) in the presence of styrene (St) by using a free-radical grafting methodology. The grafting degree (Dg) of MA was increased from 0.65 wt % to 1.1 wt % with the St/MA ratio up to 2/1, where the grafting efficiency (Eg) of MA was 27%. However, both Dg and Eg were decreased with further increasing of the St/MA ratio to 4/1. The Dg of MA increased with MA concentration and showed a maximum at 180 °C in the temperature range of 165 °C–190 °C. The grafting mechanisms of MA in the presence of St are analyzed based on titration, thermogravimetric analysis and infrared results, i.e., MA is grafted onto PLA chains via single monomers and a charge-transfer-complex (CTC) at St/MA ratios of ≤ 1/1, while dominantly via St-co-MA oligomers at St/MA ratios of around 2/1. Copolymerization rather than grafting of St and MA occurs at St/MA ratios of around 4/1. The thermal stability of PLA was compromised to a certain extent by the grafting of MA, resulting in reductions in the decomposition temperature (Td-5%) and molecular weight of the PLA. In addition, the crystallization and melting temperatures of the PLA were slightly reduced after the grafting.

Styrene-assisted melt free-radical grafting of maleic anhydride onto poly(β-hydroxybutyrate)

Maleic anhydride (MA) was grafted onto poly(β-hydroxybutyrate) (PHB) chains by using styrene (St) as co-monomer and dicumyl peroxide (DCP) as free-radical initiator. The grafting degree of MA was increased from 0.2 wt% to 0.9 wt% with the St/MA ratio up to 2/1. The St-assisted grafting mechanisms are revealed based on titration, thermogravimetric analysis and infrared analysis, i.e. MA is grafted onto PHB chains by way of single monomers and charge-transfer-complex (CTC) at the St/MA ratios of ≤1/1, while St-co-MA oligomers are the dominating grafting pendants when the St/MA ratios ≥2/1. The decomposition temperature (Td-5%) of PHB is raised by approx. 35 °C after grafting of the MA and/or short St/MA pendants, meanwhile higher molecular weight of the PHB is obtained. In addition, the crystallization of PHB is promoted by grafting of the MA or MA-co-St oligomers. The crystallization mechanism of maleated PHB is proposed as well.

Morphology and properties of compatibilized polylactide/thermoplastic starch blends

This paper investigates the properties and interfacial modification of blends of polylactide (PLA) and glycerol-plasticized thermoplastic starch (TPS). A twin-screw extrusion process was used to gelatinize the starch, devolatilize the water to obtain a water-free TPS and then to blend into the PLA matrix. The investigated TPS concentration ranged from 27 to 60wt%. In the absence of interfacial modification, the TPS/PLA blend morphology observed through scanning electron microscopy was very coarse with TPS particles sizes between 5 and 30μm. Interfacial modification was achieved by free-radical grafting of maleic anhydride (MA) unto the PLA and then by reacting the modified PLA with the starch macromolecules. Blends comprising MA-grafted PLA showed much finer dispersed phase size, in the 1–3μm range and exhibited a dramatic improvement in ductility. The paper discusses the effects of two interfacial modification strategies on the blend morphology and tensile properties and investigates the compatibilization efficiency for glycerol plasticizer contents between 30 and 39wt% and for starches from three different sources: wheat, pea and rice.

Maleic anhydride grafting of polypropylene: peroxide and solvent effects

The grafting of polyolefins with maleic anhydride (MA) has been incorporated into industrial practice to generate copolymers that can act as coupling agents between the non-polar polyolefins and different polar fillers and reinforcements. In the present study, two different peroxides were used to initiate the MA grafting onto polypropylene (PP), namely dicumyl peroxide (DCP) and 1,3-bis (terbutylisopropyl peroxi)benzene (DIBP). The use of DIBP allowed similar grafting yields to DCP to be obtained, but with less chain scission of the polyolefin. Moreover, the utilisation of a coagent, toluene (Tol), leads to a reduction in the chain scission of PP. A monotonous decrease in the melt flow index (MFI) of the polymer was observed with increasing molar ratio of Tol/MA, in the range of ratios considered (0–2·5). In addition, the free radical grafting of MA onto PP remained high and optimum grafting was obtained for a molar ratio Tol/MA of ∼0·5. It was observed that the addition of toluene was effective, independent of the reaction process utilised, namely batch mixing or extrusion.

A look inside the extruder: evolution of chemistry, morphology and rheology along the extruder axis during reactive processing and blending

A simple device was recently developed for fast sampling (within a few seconds) of representative melt samples (about 2 g) on a running extruder. An array of such devices has been mounted on a twin-screw extruder. The goal of this study was to de-black-box reactive processing of polymers by studying some typical examples. - Processing of polyolefins in the presence of peroxides: when the polymer is molten and the melt temperature is sufficiently high branching/cross-linking of PE and degradation of PP occurs; the conversion follows a convex profile along the screw axis, which profile is similar to the exponential profile calculated for peroxide decomposition. - Free-radical grafting of maleic anhydride (MA) onto polyolefins: MA grafting onto PE and PP also follows a convex profile with branching/cross-linking as parallel side reaction for PE and degradation for PP; for PE degradation of the formed grafted/cross-linked gel is observed at the end of the extruder. - Reactive blending of PA-6 with EPM-g-MA: within a few seconds the in-situ compatibilization reaction, resulting in PA-6/EPM graft copolymers, is completed and the degree of rubber dispersion has changed from the mm to the sub-μm range, regardless of the MA content of EPM-g-MA and the EPM-g-MA content of the blend; PA degradation occurs along the whole extruder.

Maleation of Poly(4-methyl-1-pentene) Using Supercritical Carbon Dioxide.

The heterogeneous free-radical grafting of maleic anhydride (MAH) onto poly(4-methyl-1-pentene) (PMP) was studied using supercritical carbon dioxide as the solvent/swellant. The anhydride content in the product can be controlled by using variations in time and temperature to achieve maleations as high as 7 mol % at 125 degreesC after a 5 h reaction period. A comparison between benzoyl peroxide (BPO) and dicumyl peroxide (DCP) initiators indicates that DCP is the more effective initiator. The effect of reactant concentrations on the degree of grafting is also examined, yielding an optimum MAH:DCP molar ratio of 3:2. Competitive cross-linking of the substrate is the major drawback to this means of polymer modification.

Exchange and free radical grafting reactions in reactive extrusion

AbstractThe potential of two types of reactions for reactive extrusion was evaluated in our laboratory: exchange reactions of copolyesters and free radical grafting of monomers onto polyolefins. Specifically, the alcoholysis of ethylene and vinyl acetate copolymers, the transesterification of ethylene and alkyl acrylate copolymers (EAA) and the aminolysis of alkyl acrylate copolymers were investigated as the exchange reactions while the grafting of maleic anhydride (MA) onto polypropylene (PP) as the free radical reactions. The exchange reactions are very slow without catalysts. Tin derivatives, such as dibutyl tin dilaurate (DBTDL) and dibutyl tin oxide (DBTO), are good catalysts for the alcoholysis and the transesterification, but not for the aminolysis. For the latter, tautomeric compounds, such as 2‐pyridone and 2‐mercaptopyridone, are efficient. Comparative kinetic studies showed that, for all the three exchange reactions, the reacting medium (solution or the homogeneous melt) does not affect their reaction mechanisms nor their intrinsic rate constants. Additionally, mechanical mixing does not contribute to the overall reactions. As for the free radical grafting of MA, the presence of electron‐donating monomers and styrene (ST) in particular was shown to be very effective in improving the grafting yield while minimising the degradation of PP. This was proven to be due to the formation of a charge transfer complex between MA and such a monomer.