Factors Affecting Surfactant Distribution in Pressure-Sensitive Adhesives during Film Formation and Ageing

影响压敏胶成膜和老化过程中表面活性剂分布的因素

• 批准号: 2123132
• 金额: --
• 依托单位: University of Surrey
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2123132
• 关键词: Factors; Affecting; Surfactant; Distribution; Pressure

Pressure-sensitive adhesives (PSAs) adhere to nearly any surface under the application of light pressure. They are used in everyday life with applications such as tapes, labels, graphics, coatings on cars and in some medical devices. PSAs have historically been manufactured from viscoelastic (soft) polymers dissolved in organic solvents. Upon casting the PSA solution the organic solvent evaporates away, leaving the film behind. Nowadays, in order to avoid the emission of the organic solvents into the atmosphere, which can have detrimental effects on the environment, PSAs are increasingly being made using colloidal polymer dispersions in water, known as latex. In order to synthesise latex, emulsion polymerisation is used, which requires the use of soap-like molecules, called surfactants. Surfactants aid the stability of the latex dispersions and are essential to the process. Unfortunately, surfactants have been shown to cause detrimental effects on the properties of PSAs, such as a loss of optical clarity due to light scattering from unwanted water sorption and a loss of adhesion when surfactants have migrated to the surface of the PSA.The aim of this research is to understand the factors that affect the non-uniform distribution of surfactants in PSAs, and to determine whether the mechanisms can be controlled. Since surfactants can accumulate either during the film formation (drying) stage, or during the ageing of the PSA once in the dry state, the research will focus on both of these two scenarios. Recent mathematical models have predicted that several key factors have an effect on the distribution of surfactants throughout the film formation stage. The water evaporation rate, temperature, particle size, film thickness and viscosity (polymer and water phase) have all been predicted to play a role. In this project, experiments will be designed to test the models in a systematic way, and attempt to provide clarity with respect to the role that each of the identified factors plays on the final surfactant distribution.The research will also investigate whether induced electric fields from ionic surfactant gradients that develop in the PSAs during the drying process could drive particle motion via the mechanism of electrophoresis. Current models of surfactant distribution during film formation do not consider the effects of electrophoresis, but it might be important. Depth profiles of the surfactants will be determined via Rutherford Back Scattering (RBS) for heavy elements, such as the cations, and Elastic Recoil Detection (ERD) for deuterium and hydrogen at the Surrey Ion Beam Centre. The surfactant distributions will be compared with increasing contributions of ionic concentration gradients.In relation to PSA film ageing, previous experimental studies have suggested that humidity can have an effect on surfactant distribution during the dry state, during ageing studies. Unfortunately these experiments had limited scope, and the results were not correlated with mechanical performance of the PSAs. In this work we will age two commercial PSAs at 0%, 42% and 85% relative humidity for 6 months and determine changes to the surface composition and adhesive properties. The films will be cast onto PET sheets (or glass plates) and covered with a silicone release liner for storage. Water vapour sorption will be measured independently. Adhesion measurements (peel, loop, and probe) will be, performed initially and after ageing. Qualitative investigations into the surface structure and composition of the films during ageing will be made using atomic force microscopy (AFM). Complementary measurements of surface composition will be made using SIMS analysis. Any changes in adhesive properties will be correlated with changes in nanostructure and surface composition.The project will be conducted in collaboration with Synthomer plc.

压敏胶（psa）在光压作用下几乎可以粘附在任何表面上。它们在日常生活中使用，如胶带、标签、图形、汽车涂层和一些医疗设备。psa历来是由粘弹性（软）聚合物溶解在有机溶剂中制造的。在铸造PSA溶液时，有机溶剂蒸发掉，留下薄膜。如今，为了避免有机溶剂排放到大气中，这可能对环境产生有害影响，越来越多的psa使用胶体聚合物分散在水中，被称为乳胶。为了合成乳胶，需要使用乳液聚合，这需要使用类似肥皂的分子，称为表面活性剂。表面活性剂有助于乳胶分散体的稳定性，对该工艺至关重要。不幸的是，表面活性剂已被证明会对PSA的性能造成有害影响，例如，由于不需要的水吸附引起的光散射导致光学清晰度的损失，以及当表面活性剂迁移到PSA表面时附着力的损失。本研究的目的是了解影响表面活性剂在psa中不均匀分布的因素，并确定其机制是否可以控制。由于表面活性剂既可以在成膜（干燥）阶段积累，也可以在干燥状态下的PSA老化过程中积累，因此研究将集中在这两种情况下。最近的数学模型预测，在整个成膜阶段，有几个关键因素会影响表面活性剂的分布。水的蒸发速率、温度、颗粒大小、薄膜厚度和粘度（聚合物和水相）都被预测会起作用。在本项目中，将设计实验以系统的方式测试模型，并试图明确每个确定的因素在最终表面活性剂分布中的作用。研究还将探讨干燥过程中离子表面活性剂梯度产生的感应电场是否可以通过电泳机制驱动粒子运动。目前的表面活性剂在成膜过程中的分布模型没有考虑电泳的影响，但它可能是重要的。表面活性剂的深度分布将通过卢瑟福反向散射（RBS）测定重元素，如阳离子，以及萨里离子束中心的弹性反冲探测（ERD）测定氘和氢。表面活性剂的分布将与离子浓度梯度的增加的贡献进行比较。关于PSA膜老化，先前的实验研究表明，在干燥状态下，在老化研究期间，湿度会影响表面活性剂的分布。不幸的是，这些实验的范围有限，结果与psa的机械性能不相关。在这项工作中，我们将在0%，42%和85%的相对湿度下老化两个商业psa 6个月，并确定表面成分和粘合性能的变化。这些薄膜将被浇铸到PET片（或玻璃板）上，并覆盖一层硅树脂释放衬垫用于存储。水蒸气吸收量将单独测量。粘合测量（剥离，环和探头）将进行，最初和老化后。在老化过程中，将使用原子力显微镜（AFM）对薄膜的表面结构和组成进行定性研究。将使用SIMS分析对表面成分进行补充测量。粘合剂性能的任何变化都与纳米结构和表面成分的变化有关。该项目将与Synthomer plc合作进行。