Investigation of the Gum Stock Behavior of Polyurethane Crosslinking Matrix by Adding Triol Diol Mixtures for the Application of Composite Solid Rocket Propellants

The addition of some advanced additives to improve the mechanical properties of polyurethane (PU) polymeric matrix, which acts as a binder system in composite solid rocket propellants (CSRPs), is a target for the energetic materials researchers. In this investigation, 45 compositions of different crosslinked PU matrices were produced to demonstrate the effect of adding crosslinking mixture (CM) on the mechanical capabilities of polyurethane gum stock. The crosslinking mixture (CM) is composed of a triol crosslinker, trimethylolpropane (TMP), and a chain extender, 1,4-butanediol (BD). For comparison, traditional PU samples without crosslinking additives were formulated. As a prepolymer, HTPB was used with a curing agent (HMDI). The research was carried out with different ratios of TMP to BD, different curing ratios (NCO/OH=0.7, 0.9, and 1.1), and crosslinking mixture contents in the range of 0-5 wt.%. The mechanical characteristics of all the cured formulations were measured. It was demonstrated that changing the ratio of TMP to BD has a significant impact on the mechanical performance causing a wide range of elongation and strength qualities. Increasing the wt.% of triol crosslinker in the sample enhanced the tensile strength, whereas the strain has been decreased. The addition of diol chain extender increased the strain rate of the samples. The mechanical parameters were adjusted simply by employing the crosslinking ingredients to get exceptional mechanical characteristics at each NCO/OH curing ratios. Also it was concluded that PU samples of curing ratio (NCO/OH= 0.7-0.9) with TMP:BD (1:1) showed a promising results and could be used according to the requirements of the rocket system designers

Grand Challenges in global eye health: a global prioritisation process using Delphi method

Background: We undertook a Grand Challenges in Global Eye Health prioritisation exercise to identify the key issues that must be addressed to improve eye health in the context of an ageing population, to eliminate persistent inequities in health-care access, and to mitigate widespread resource limitations. Methods: Drawing on methods used in previous Grand Challenges studies, we used a multi-step recruitment strategy to assemble a diverse panel of individuals from a range of disciplines relevant to global eye health from all regions globally to participate in a three-round, online, Delphi-like, prioritisation process to nominate and rank challenges in global eye health. Through this process, we developed both global and regional priority lists. Findings: Between Sept 1 and Dec 12, 2019, 470 individuals complete round 1 of the process, of whom 336 completed all three rounds (round 2 between Feb 26 and March 18, 2020, and round 3 between April 2 and April 25, 2020) 156 (46%) of 336 were women, 180 (54%) were men. The proportion of participants who worked in each region ranged from 104 (31%) in sub-Saharan Africa to 21 (6%) in central Europe, eastern Europe, and in central Asia. Of 85 unique challenges identified after round 1, 16 challenges were prioritised at the global level; six focused on detection and treatment of conditions (cataract, refractive error, glaucoma, diabetic retinopathy, services for children and screening for early detection), two focused on addressing shortages in human resource capacity, five on other health service and policy factors (including strengthening policies, integration, health information systems, and budget allocation), and three on improving access to care and promoting equity. Interpretation: This list of Grand Challenges serves as a starting point for immediate action by funders to guide investment in research and innovation in eye health. It challenges researchers, clinicians, and policy makers to build collaborations to address specific challenges. Funding: The Queen Elizabeth Diamond Jubilee Trust, Moorfields Eye Charity, National Institute for Health Research Moorfields Biomedical Research Centre, Wellcome Trust, Sightsavers, The Fred Hollows Foundation, The Seva Foundation, British Council for the Prevention of Blindness, and Christian Blind Mission. Translations: For the French, Spanish, Chinese, Portuguese, Arabic and Persian translations of the abstract see Supplementary Materials section.</p