Film Formation and Mechanical Behavior of Polymer Latices

Abstract

The aim of this work is to obtain relevant information on the film forming process in order to control the development of mechanical properties of the latex film. As appropriate mechanical behavior cannot be reached if coalescence is not achieved, we first investigate the coalescence of the core-shell latex by performing weight loss measurements at different temperatures and humidities. After a brief survey of the literature, we propose a model of coalescence with a new description of the deformation of latex beads, based on the diffusion of structural units under the polymer / water interfacial forces. Calculations based on this model suggests that particle deformation and water evaporation may display different kinetics. Therefore, the end of coalescence may be related to the slowest process. At the end of coalescence stage, mechanical behavior of the film can be investigated. Then, we perform tensile tests for different time of annealing during the autohesion phenomenon. During this film forming stage, the behavior of the film changes drastically from brittle to ductile. We observe two distinct evolution for strain at break and stress at rupture. The former is attributed to the formation of entanglements through the particles boundaries whereas the latter might concern water diffusion throughout the film.The process consisting of driving a latex from its colloidal form to a continuous film needs a good understanding since it is of great importance for industry. Film formation is a critical aspect of all applications that involve coating a surface or forming a layer with good cohesive properties. Consequently, great efforts have been devoted to the study of this phenomenon.Several stages during film formation have been observed experimentally and a phenomenological description of the process, divided into three parts, is generally accepted (1) :

Influence of the Particle Size and Particle Size Ratio on the Morphology and Viscoelastic Properties of Bimodal Hard/Soft Latex Blends

“…The one area of polymer blends that has been virtually ignored involves simple latex blends. Recently, an increasing number of publications have appeared − that investigate the characteristics of film formation and the mechanical film properties of blends of polymer dispersions.…”

Porous Particle-Polymer Composites

“…Drying such composites too quickly can leave polymer films in a brittle state. Time should be allowed for the formation of polymer chain entanglements, which give rise to greater ductility within the cohered film (Gauthier et al 1996). Film formation can be summarised accordingly (Steward et al 2000): -Evaporation, particle concentration and ordering -Particle deformations, compaction and cohesion -Polymer chain diffusion across particle boundaries Mineral particle surfaces, following surface treatments with dispersing agents or surfactants, may comprise carboxylate groups.…”

Using Pyrene Excimer Fluorescence To Probe Polymer Diffusion in Latex Films

“…It is during this final stage of film formation that a film develops both its mechanical integrity and the ability to protect a surface. 1,3,4 As such, the quantitative determination of the extent of coalescence between particles is of high interest.…”

“…One main usage of latex dispersions is for decorative and protective purposes, where a latex dispersion is applied onto a surface to form a film. Film formation is typically divided into three stages: water evaporation, particle deformation, and particle coalescence. − In the first stage, a latex dispersion is deposited on a substrate and the water is allowed to evaporate, leaving a layer of packed particles. In order for the subsequent stages of film formation to occur, the film must be heated above a minimum temperature, namely the minimum film formation temperature (MFT).…”

“…With continued annealing of the film, the polymer chains constituting the latex particles begin to diffuse across the particle boundaries in a process that ultimately leads to coalescence of the particles into a continuous film. It is during this final stage of film formation that a film develops both its mechanical integrity and the ability to protect a surface. ,, As such, the quantitative determination of the extent of coalescence between particles is of high interest.…”