Descripció del projecte
Pressure-sensitive adhesives (PSAs) have been in wide use since the late 19th century, starting with medical tapes and dressings. The first U.S. patent describing the use of a PSA -or a soft, adhering bandage- was issued in 1846. Ninety years later Stanton Avery developed and introduced the self-adhesive label. Two major industries resulted from these innovations: pressure-sensitive tapes and labels. Industrial tapes were introduced in the 1920s and 1930s followed by self-adhesive labels in 1935. About ten years after that, pressure-sensitive protective films were manufactured. PSAs, as adhesives, only need a little pressure to stick things they want to stick well, and the initial and subsequent persistent stickness are good. Another thing is very good: it can be used repeatedly when it is not contaminated by othe objects, and it usually does not destroy trhe surface of the adhesive after use.
PSAs can be prepared by a variety of polymerization processes, including bulk, solvent, and emulsion polymerization. Emulsion polymerization is a heterogeneous process which produces polymer colloidal dispersions, called latexes, with particles sizes from 50 nanometers to 1 micra. The main disadvantages of emulsion systems are their multiphase character and complex mechanisms, hindering the knowledge of the process and the control of final properties of the product. However, the advantages of emulsion polymerization makes this technique very useful for wide industrial applications. The aqueous continuous phase can absorb abd dissipate the heat generated by the exothermic free radical polymerization. This means that the reactor temperature can be controlled easily thanks to the high heat capacity of water. On the other hand, in emulsion systems, polymerization occurs in the monomer-swollen latex particles. Therefore, greater rates of polymerization and higher molecular weigths are achieved than in an equivalent bulk process. Furthermore, from an envieromental point of view, the process can be carried out through to relatively high conversion of monomer into polymer, hence problems with residual monomers are minimed; and the product obtained is an aqueous dispersion, wich reduces both safety and environmental hazards.
At present, PSAs are predominately made from monomers based on petroleum products. With the increasing cost and limited supply of oil, the use of rewenable resources as raw material components for PSAs has become economically attractive and socially responsible. The limited production capacity of the acrylic monomers used in acrylic PSAs is another driving force for investigating alternate sources. Furthermore, a performance advantage of bio-based PSAs could include biodegradability, which supports the environmental friendliness of these adhesives. The present project will deal with these needs.
This project will tackle the preparation, characterization and final application of different families of PSAs (bio-based and conventional) by using the very well stablished know-how of IQOXE emulsion polymers. Different emulsion polymerization processes will be carried out varying reaction conditions and raw materials. In this sense, bimodal particles sizes and molecular weights are desired to obtain the PSAs with the best properties (tack, peel stregth and shear resistance). To the best of our knowledge, the surfactant play an important role in the process and the use of an bio-based surfactat could be the key to prepare the perfect PSA. Commonly, low molecular molecular weight surfactants are used. However, the use of amphiphilic block copolymer surfactants impart several advantages to the properties of the resulting emulsion because exhibit unique properties in aqueous solution owing their low critical aggregation concentration and low diffusion coefficient compared to those of conventional short-chain stabilizers. Taking advantage of previous expertise in the group at URV, a library of biobased amphiphilic block copolymers from various renewable resources will be prepared by controlled radical polymerization and evaluated as stabilizers in the above mentioned formulations.
