Evaluate the nonlinear viscoelasticity of polyolefin melts using the Larson model

[[abstract]]Nonlinear rheological properties of polyolefins have long been studied and predicted by using the Larson model with the damping function generally obtained from the stress relaxation measurements. In this study, we investigate the nonlinear rheological properties of high density polyethylene (HDPE) and polypropylene (PP) using the Larson model with damping functions obtained from either the dynamic frequency sweep or the stress relaxation test. Experimental measurements and their corresponding model predictions for the rheological parameters were then compared to evaluate the applicability of the Larson model to the nonlinear rheology, and the following conclusions could be achieved. The steady shear viscosity could be satisfactorily described by the Larson model with the damping functions obtained from the two different methods, except at shear rates higher than 103 s-1. The predicted first normal stresses also account for the measured data, except for those using the stress relaxation data showing a little deviation for the PP sample. In addition, the predictions for elongation viscosity are also in good agreement with the experimental results within the short range of elongation rate achieved in this work.[[notice]]補正完畢[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子

Tree basal area as an index of thermal cover for elk /

no.42

Solid-state polymerization of poly(ethylene terephthalate): Effect of organoclay concentration

Poly(ethylene terephthalate) (PET)/Cloisite 30B (C30B) nanocomposites of different organoclay concentrations were prepared using a water-assisted extrusion process. The reduction of the molecular weight (Mw) of the PET matrix, caused by hydrolysis during water-assisted extrusion, was compensated by subsequent solid-state polymerization (SSP). Viscometry, titration, rheological, and dynamic scanning calorimetry measurements were used to analyze the samples from SSP. The weight-average molecular weight (Mw) of PET increased significantly through SSP. PET nanocomposites exhibited solid-like rheological behavior, and the complex viscosity at high frequencies was scaled with the Mw of PET. The Maron-Pierce model was used to evaluate the Mw of PET in the nanocomposites before and after SSP. It was found that the extent and the rate of the SSP reaction in nanocomposites were lower than those for the neat PETs, due to the barrier effect of clay platelets. Consequently, the SSP rate of PET increased with decreasing particle size for the neat PET and PET nanocomposites. The effect of the Mw of PET on the crystallization temperature, crystallinity, and the half-time, t1/2, of nonisothermal crystallization was also investigated. With increasing Mw of PET, t1/2 increased, whereas Tc and Xc decreased.Peer reviewed: YesNRC publication: Ye

Preventing EMS workplace violence: A mixed-methods analysis of insights from assaulted medics

Objective: To describe measures that assaulted EMS personnel believe will help prevent violence against EMS personnel. Methods: This mixed- methods study includes a thematic analysis and directed content analysis of one survey question that asked the victims of workplace violence how the incident might have been prevented. Results: Of 1778 survey respondents, 633 reported being assaulted in the previous 12 months; 203 of them believed the incident could have been prevented and 193 of them (95%) answered this question. Six themes were identified using Haddon's Matrix as a framework. The themes included: Human factors, including specialized training related to specific populations and de-escalation techniques as well as improved situational awareness; Equipment factors, such as restraint equipment and resources; and, Operational and environment factors, including advanced warning systems. Persons who could have prevented the violence were identified as police, self, other professionals, partners and dispatchers. Restraints and training were suggested as violence-prevention tools and methods Conclusions: This is the first international study from the perspective of victimized EMS personnel, to report on ways that violence could be prevented. Ambulance agencies should consider these suggestions and work with researchers to evaluate risks at the agency level and to develop, implement and test interventions to reduce the risks of violence against EMS personnel. These teams should work together to both form an evidence-base for prevention and to publish findings so that EMS medical directors, administrators and professionals around the world can learn from each experience. © 2018 Elsevier Lt