Twin‐screw extrusion processes are commonly refined on laboratory‐scale extruders then scaled‐up to manufacturing systems. When using twin‐screw extrusion to compound filler into a polymer, the dispersion of the filler must be considered during scale‐up. In this work, two scale‐up methods are evaluated for how accurately they scale dispersion as measured by the Residence Stress Distribution, an experimental method that quantifies stress developed in a twin‐screw extruder. The first scale‐up method evaluated is the industry‐standard scaling based on maintaining equivalent volumetric flow rate across extruder sizes. Volumetric scaling is compared to a second, novel scale‐up method, the percent drag flow rule, which maintains the same degree of fill in the strongest dispersive screw elements on all extruder sizes. Both scale‐up rules have been used to scale between three extruder sizes and have been evaluated for how accurately the larger extruders recreate the dispersive mixing of the smallest machine. Results indicate that the percent drag flow scale‐up more accurately maintains dispersive mixing behavior than the volumetric scaling. Furthermore, percent drag flow scale‐up resulted in all three extruder sizes behaving similarly to changes in operating conditions. These results indicate that percent drag flow scale‐up is a valid technique to scale real industrial processes. POLYM. ENG. SCI., 57:345–354, 2017. © 2016 Society of Plastics Engineers

Twin-screw polymer extrusion has shown increased utility for creating composite materials. However, in order to achieve the desired product properties, sufficient mixing is essential. Dispersive mixing, or the breaking-up of particle agglomerates, is critical to create filled compounds with the required material properties. In a twin-screw compounding process, the Residence Stress Distribution (RSD) has been used to quantify the dispersive mixing induced by the stresses in the polymer melt. These stresses are quantified by the percent break-up of stress-sensitive polymeric beads. It was found that the amount of material that experiences the critical stress is a function of the operating conditions of screw speed and specific throughput [1]. The quantification of dispersive mixing allows for better control of a compounding process and can be used to design new processes. During the development of a new compounding process, screw geometries and operating conditions are often refined on a laboratory-scale extruder and then scaled up to a manufacturing level. Scale-up rules are used to translate the operating conditions of a process to different sizes of extruders. In a compounding process, the goal when scaling-up is to maintain the same material properties on both scales by achieving equivalent mixing. The RSD methodology can be used to evaluate the effectiveness of scale-up rules by comparison between two or more scales. This paper will demonstrate the utility of the RSD in evaluation of two unique scale-up rules. Conventional industry practice is based on the volumetric flow comparison between extruders. The proposed approach demonstrates that in order to maintain equivalent dispersive mixing between different sizes of extruders, the degree of fill, or the percent drag flow (%DF), must be kept equivalent in the primary mixing region. The effectiveness of both rules has been evaluated by experimental application of the RSD methodology. A design of experiment approach was used to generate predictive equations for each scale-up rule that were compared to the behavior of the original small-scale extruder. Statistical comparison of the two scale-up rules showed that the %DF rule predicted operating conditions on the large-scale extruder that produced percent break-up behavior more similar to the small-scale behavior. From these results, it can be concluded that the %DF scale-up rule can be used to accurately scale operating conditions between different-sized extruders to ensure similar dispersive mixing between two processes. This will allow for greater accuracy when recreating the material properties of a small-scale twin-screw compounding process on a larger, mass production machine.

Background and Objectives Due to the concern over global rising rates of dementia, increased emphasis has been placed on understanding and moulding the public’s knowledge and awareness of the condition. There has been limited previous research into predictors of dementia knowledge; overall knowledge amongst the public is low, and it has been widely agreed that more needs to be done to raise awareness of this condition. This study seeks to solidify understanding of public dementia knowledge and introduces dementia worry, motivation to seek information and risk perception as novel concomitants of this knowledge. Research Design and Methods A convenience sample of 311 UK adults completed a survey on dementia knowledge including Alzheimer’s disease-specific questions, worry about developing dementia, motivation to seek information and perceived personal risk of getting the disease. Surveys were completed face-to-face and included both closed and open-ended questions. Results Overall dementia knowledge scores were low, achieving an average of 33% of the total possible score, with 88% of the sample scoring below 50%. Bivariate correlations were performed between dementia knowledge and key variables, revealing significant positive relationships with risk perception ( r = 0.179, p = .002), worry ( r = 0.140, p = .016) and motivation to seek information ( r = 0.139, p = .016). When knowledge was dichotomised into high and low, worry about ( p = .28) and perceived risk ( p = .19) of dementia was significantly lower for people with low knowledge scores than for people with higher dementia knowledge scores. Motivation to seek information was not significantly different between the high and low knowledge groups ( p = .071). Discussion and Implications Despite the relatively low knowledge scores, findings show a positive relationship between modifiable factors and dementia knowledge, suggesting areas to consider for both further research and publication campaigns. Further implications and limitations of this study are discussed.