Effects of Screw Configurations on the Grafting of Maleic Anhydride III
Processing
In the reactive extrusion, the sampling was performed at distances of 400, 560, 840, and 950 mm (the die exit) from the feeding port. To avoid further reaction, the specimens were dipped into liquid nitrogen immediately after being collected from the twin screw extruder. To eliminate the residual monomer, the grafted products were dissolved in xylene under reflux until a clear solution was obtained. These solutions were then precipitated in acetone and filtered to obtain the purified products. In the end, the filter mass was dried in a vacuum oven for 24 h at 1108C.
All of the purified specimens were tested for the GD by neutralization titration. Grafted LDPE (0.2 g) was dissolved in 50 mL of xylene at the boiling temperature. When the samples were fully soluble, two to three drops of a colored indicator and excessive KOH–ethanol were added until the solution turned red. Then, HCl–ethanol was added, and the titration was stopped immediately at the visual endpoint when the color changed.
when the extrusion process was stable, the clam-shell barrel was quenched with cooling water. The carcass was collected after the clam-shell barrels were removed and was further used not only to identify the melting endpoint but also to measure the degree of fill in the kneading blocks.
A pulse stimulus response technique was used to obtain the data for RTD. A blue master batch as a tracer was added to the feeding port after the extrusion reached stable status. The extrudate was collected from the moment right after the feeding of the tracer into the feeding port to the point when all the tracers exited the die. The a* value (of the L*a*b* color space) was used as the measurement of the tracer concentration in the extru applied, which represents the variation of the concentration of the tracer at the die exit with time.The mean residence time (t) and the RTD spread around the mean (r2; also called the variance) were introduced as well.
Because in reactive extrusion the reactant system of LDPE and MA is an immiscible liquid–liquid sys- tem, in the fourth group of extrusion experiments, an ABS/PC blend as an immiscible system was introduced to evaluate the mixing performance of each screw configuration. The ABS/PC blend extru- date was collected and then cryogenically fractured along the surface transverse to the extrusion direction. After the fractured samples were coated with gold, they were examined with a Hitachi S-4700 field emission scanning electron microscope (Tokyo, Japan) to check the size of the dispersed phase, that is, PC.The scanning electron microscopy (SEM) pictures were quantitatively analyzed by the counting of the size of the dispersed phase from different fields of the specimen.
