Knowledge-based control of emulsion polymerization: Tailoring adhesive properties

Abstract

An on-line control strategy to produce copolymer latexes with desired adhesive properties (resistance to shear and resistance to peel) has been developed. The strategy required a quantitative model relating adhesive properties and molecular weight distribution that was built using partial least squares regression. The model was used to determine the set-point trajectories of the monomers and chain transfer agent that are used as manipulated variables in the control strategy. The control strategy was experimentally verified to produce an n-butyl acrylate/styrene copolymer latex with a resistance to shear of 1310 s and resistance to peel of 3.1 N/100 mm.A good control strategy for emulsion polymerization reactions must assure that a product with the desired final properties will be obtained. Unfortunately, most of the control strategies developed until now only allow for the control of the molecular properties of the polymer by manipulation of several process variables, 1-7 without including the final properties of the product in the control strategy.Historically, end-use and molecular properties of the product have been related using trial and error procedures, which are in most cases, highly time-consuming. This work is an attempt to relate those properties in a quantitative and reliable way and to include such a relationship in a control strategy in order to directly provide a product with the desired end-use properties.An important application of acrylic latexes is as pressure sensitive adhesives (PSAs), mainly used for labels, tapes, decorative films, protective materials, and wall and floor coverings. Each specific application requires appropriate end-use properties, characterized by a combination of specific values of adhesive properties such as tackiness, resistance to peel, and resistance to shear.It has been proved that several molecular properties of a latex, such as copolymer composition, average molecular weight and molecular weight distribution, level of branching, content of gel, and crosslinking, strongly affect the values of the adhesive properties. [8][9][10][11][12][13] The glass transition temperature (T g ) of the copolymer, which depends on the copolymer composition, determines to a very large extent the tackiness of the final product. 8 The adhesive performance is also affected by the composition profile. 9 Dale et al. 10 reported on the effect of crosslinking on the properties of acrylic adhesives, concluding that the crosslinking density should be low for a PSA, because a high degree of crosslinking, which severely affects tack and peel adhesion, may yield to a nontacky product. The gel content also affects the mechanical properties of the final product. 11-13 Generally, the presence of gel increases the resistance to peel and the resistance to shear and decreases the tack, although above certain levels of gel, resistance to both shear and peel dramatically decreased. 12,13 Resistance to shear and to peel depend also on the molecular weight of the polymer. 14,15 Although there are some qual...

Independent control of sol molar mass and gel content in acrylate polymer/latexes

“…Each specific application requires appropriate end-uses properties, characterized by a combination of specific values of tackiness, resistance to shear and resistance to peel. It has been proven that several latex properties, such as copolymer composition, molar mass distribution, gel content, and cross-linking density strongly affect the values of the adhesive properties [16][17][18][19][20][21][22].…”

Emulsion Polymerization

“…In order to reduce this time-consuming methodology semiempirical approaches can be used. An example of this type of approach was recently reported to relate the MWD of an acrylic latex of a given composition and the adhesive properties [160,161].…”

“…This can be achieved by inverting the model using appropriate techniques of optimization or neural networks [160,161].…”

Emulsion polymerization: From fundamental mechanisms to process developments

“…To implement the strategy outlined in Figure 1, it is necessary to translate the ultimate product performance in terms of polymer microstructure by means of quantitative polymer micro‐structure–property relationships. Although examples of quantitative micro‐structure–property relationships are available (e.g., for the effect of copolymer composition profile82 and MWD83, 84 on adhesive properties and for the effect of PSD on latex rheology85), much work is needed in this area.…”