Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

No abstract

The reaction rates, in the base-catalysed acetylation of gelatinised aqueous starch (4 wt%), by vinylacetate (ViAc), were investigated in a semibatch reactor at temperatures ranging from 20 to 50°C. The desired starch acetylation reaction is accompanied by an undesired parallel base-catalysed hydrolysis reaction of vinylacetate and a consecutive hydrolysis reaction of the acetylated starch. The rate equations are: Starch acetylation: &AC =-k, cvic CRO-Starch acetate hydrolysis: &A= =-kz CRAM con-Vinylacetate hydrolysis: &tic =-k3 CViAc COW where k1,2,3 = k1,2,3, cHIO, CViAc is the vinylacetate concentration, cRo-is the concentration of the dissociated starch hydroxyl group, cRAc is the concentration of acetylated starch and con-is the sodium hydroxide concentration; k is the reaction rate constant. The temperature dependency of the rate constants was measured as: Acetylation of starch: Deacetylation of the starch ester: Hydrolysis of vinylacetate: where R (gas constant) = 121.8 J/mol"C.

The grafting of polystyrene onto dissolved starch in a twin screw extruder has been studied. This copolymerization was initiated using the thermal initiators benmy1 peroxide and K&O,. As end product a mixture containing polystyrene-grafted starch, homopolymer of polystyrene and starch was obtained. Parameters like screw rotation rate, fully filled length of the extruder, wall temperature and throughput have been varied in order to obtain information about their influence on conversion, graft percentages and molecular weight of the materials formed. To increase the amount of graft points, maleic acid anhydride (MAH) was added resulting in an increased graftmg of polystyrene onto starch. Graft percentages of 60% could be achieved. The total conversion of styrene could be controlled by adjusting extruder parameters like barrel temperature, fully filled length and initiator type. Conversions of 95% were found. Molecular weights of the polystyrene formed could be controlled by adding a chain transfer agent (dodecylmercaptan) to the styrene phase. In this way the molecular welght (MJ of the styrenic part could be varied from 20,000 to 140,000. The experiments with the chain transfer agent showed that the grafkg of polystyrene onto starch is a process occurring at the interface between the dissolved starch and the styrene phase.

A novel model predicting the residence-time distribution during reactive extrusion de Graaf, R.A.; Rohde, M.; Janssen, L.P.B.M. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract-A new model for the residence-time distribution in a counter rotating twin-screw extruder is compared with experimental results obtained during the gelatinisation of starch and the grafting of polystyrene on starch. The model consists of a transfer function from which the first three moments can be derived and is based on physical principles without any adjustable parameters. In the model and during experiments, parameters like screw rotation, fully filled length and throughput have been varied. By comparing calculated residence-time distributions with the measurements conclusions about the extruder hold-up and the fully filled extruder length can be drawn. As an extra parameter, the density change of the extruded material was needed to model the residence-time distribution curve during the grafting of polystyrene on starch. ('8 1997