Melt flow control

On-line SFE-pSFC-FTIR was used to identify extractable components (additives and monomers) from a variety of nylons [392]. SFE-SFC-FID with 100% C02 and methanol-modified scC02 were used to quantitate the amount of residual caprolactam in a PA6/PA6.6 copolymer. Similarly, the more permeable PS showed various additives (Irganox 1076, phosphite AO, stearic acid - ex Zn-stearate - and mineral oil as a melt flow controller) and low-MW linear and cyclic oligomers in relatively mild SCF extraction conditions [392]. Also, antioxidants in PE have been analysed by means of coupling of SFE-SFC with IR detection [121]. Yang [393] has described SFE-SFC-FTIR for the analysis of polar compounds deposited on polymeric matrices, whereas Ikushima et al. [394] monitored the extraction of higher fatty acid esters. Despite the expectations, SFE-SFC-FTIR hyphenation in on-line additive analysis of polymers has not found widespread industrial use. While applications of SFC-FTIR and SFC-MS to the analysis of additives in polymeric matrices are not abundant, these techniques find wide application in the analysis of food and natural product components [395]. 

Chem. Descrip. Highly refined wh. mineral oil USP CAS 8020-83-5 EINECS/ELINCS 232-455-8 Uses Melt flow control agent tor crystal PS, HIPS, polyolefins, thermoplastic elastomers, other polymers internal and external lubricant in PS, PVC, PP, PE, TPE, other polymers carrier in pharmaceuticals protective coating on foods... 

Waxss. Waxes are nonpolar and are, therefore, very incompatible with PVC which makes them excellent external lubricants for this material. Partially oxidized PE wax works well as an external lubricant for PVC by delaying fusion and is almost always combined with calcium stearate for melt flow control. Although the primary function of waxes, as well as metallic soaps, fatty acid esters, and amides is lubrication, they are in fact multifunctional, as noted previously, providing slip, antiblock, and mold release properties. 

The gate is the termination of a flow channel, and is a critical functional zone in an HR system. It governs the functioning of the nozzle, regardless of whether it is located in the nozzle or inside the actual mould cavity. The gate plays the part of a thermal or mechanical valve. Gate control concerns both melt flow control and gate closure (open time). 

Highly efficient system for PE applications requiring melt flow control and low color... 

When a molten plastic is forced through a die it is found that under certain conditions there will be defects in the extrudate. In the worst case this will take the form of gross distortion of the extrudate but it can be as slight as a dullness of the surface. In most cases flow defects are to be avoided since they affect the quality of the output and the efficiency of the processing operation. However, in some cases if the flow anomaly can be controlled and reproduced, it can be used to advantage - for example, in the production of sheets with matt surface finish. Flow defects result from a combination of melt flow properties, die design and processing conditions but the exact causes and mechanisms are not completely understood. The two most common defects are... 

MW fraction increases the melt flow, thus improving the processability but at the cost of toughness, stiffness, and stress crack resistance. In addition, the improvement in performance through narrowing the MWD is restricted by the catalyst, the process hardware, and the process control limitations. Dow has developed a reactor grade HDPE of optimized breadth, peak, and shape of MWD... 

The molecular weight of the continuous phase is an important parameter that affects the mechanics and the melt flow of the end product. It can be controlled by the use of a suitable chain transfer agent (e.g., /er/-dodecyl mercaptan Ct = 4.0) or their combinations (e.g., primary mercaptans Or = 26.0 and dimeric a-methyl styrene Ct = 0.1) [132]. 

The mechanical behavior of plastics is dominated by such viscoelastic phenomena as tensile strength, elongation at breaks, stiffness, and rupture energy, which are often the controlling factors in a design. The viscous attributes of plastic melt flow are also important considerations in the fabrication of plastic products. (Chapter 8, INFLUENCE ON PERFORMANCE, Viscoelasticity). 

This same situation exists with plastics. To be successful with plastics requires experience with their melt behavior, melt-flow behavior during processing, and the process controls needed to ensure meeting the dimensions that can be achieved in a complete processing operation. Based on the plastic to be used and the equipment available for processing, certain combinations will make it possible to meet extremely tight tolerances. 

Adequate PC and its associated instrumentation are essential for product quality control. The goal in some cases is precise adherence to a single control point. In other cases, maintaining the temperature within a comparatively small range is all that is necessary. For effortless controller tuning and the lowest initial cost, the processor should select the simplest controller (of temperature, time, pressure, melt-flow, rate, etc.) that will produce the desired results. 

In the past three decades, industrial polymerization research and development aimed at controlling average polymer properties such as molecular weight averages, melt flow index and copolymer composition. These properties were modeled using either first principle models or empirical models represented by differential equations or statistical model equations. However, recent advances in polymerization chemistry, polymerization catalysis, polymer characterization techniques, and computational tools are making the molecular level design and control of polymer microstructure a reality. 

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