Browsing by Author "Costa, M.R.N."
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- Development of a modified pre-polymer method to produce NMP-free polyurethane-urea aqueous dispersionsPublication . Fernandes, Isabel P.; Costa, M.R.N.; Ferreira, Maria José; Barreiro, M.F.A modified pre-polymer process was developed for the synthesis of NMP (N-methyl-2-pyrrolidone)-free polyurethane-urea aqueous dispersions. The pre-polymer process is based on the use of dimethylol propionic acid (DMPA, hydrophilizing diol), which requires dissolution in NMP to be introduced in the reactive mixture. NMP is difficult to remove from the dispersion remaining in the final product. In this work we present a modified pre-polymer process composed by four main stages: (1) pre-polymer synthesis in two stages: (i) reaction of the isocyanate with the polyol at 80ºC, and (ii) introduction of DMPA pre-neutralized in acetone and proceeding of the reaction at 50ºC, (2) Pre-polymer dispersion in water, (3) Chain extension with a diamine; and (4) Co-solvent removal. Several dispersions were synthesized using different DMPA contents (3.0, 4.0, 5.0%, keeping the pre-neutralization degree at 100.0%), and different DMPA pre-neutralization degree (100.0 and 90.0%, using 5.0 % of DMPA). The effect of these variables in the particle size and dispersion stability was evaluated. Based on the obtained results, the modified pre-polymer process is a feasible alternative to obtain NMP-free PUD, thus fulfilling the restrictions imposed by the European Union.
- A novel view of the manufacture of polyurethane-polyurea aqueous dispersionsPublication . Fernandes, Isabel P.; Barreiro, M.F.; Costa, M.R.N.Over the past few decades, polyurethane-polyurea aqueous dispersions (PUDs) have developed a solid reputation for high performance applications, particularly in the field of adhesives and coatings. PUDs are mostly environmentally compatible products; they are totally devoid or contain only low amounts of volatile organic compounds (VOC). This is an important feature in view of the present environmental policies where governments and internal agencies are placing emphasis on developing sustainable processes, improving work conditions and reducing emissions of toxic and polluting substances into the atmosphere. Moreover, polyurethanes are known as “tailor-made” products with properties resulting from a wide diversity of raw-materials which can be combined in different ways during the synthesis. In recent years, our research group has been involved in the development of polyurethanepolyurea aqueous dispersions for various applications. With this work we intend to review this theme and describe the most recent developments. Characterization of industrial dispersions will be presented and examples of synthesis will be described.
- A novel view of the manufacture of polyurethane-polyurea aqueous dispersionsPublication . Fernandes, Isabel P.; Barreiro, M.F.; Costa, M.R.N.A novel view of the manufacture of polyurethane-polyurea aqueous dispersions. In 10th Chemical and Biological Engineering Conference. Braga. ISBN 978-972-97810-3-2 Resumo: Over the past few decades, polyurethane-polyurea aqueous dispersions (PUDs) have developed a solid reputation for high performance applications, particularly in the field of adhesives and coatings. PUDs are mostly environmentally compatible products; they are totally devoid or contain only low amounts of volatile organic compounds (VOC). This is an important feature in view of the present environmental policies where governments and internal agencies are placing emphasis on developing sustainable processes, improving work conditions and reducing emissions of toxic and polluting substances into the atmosphere. Moreover, polyurethanes are known as “tailor-made” products with properties resulting from a wide diversity of raw-materials which can be combined in different ways during the synthesis. In recent years, our research group has been involved in the development of polyurethanepolyurea aqueous dispersions for various applications. With this work we intend to review this theme and describe the most recent developments. Characterization of industrial dispersions will be presented and examples of synthesis will be described.
- Solvent-free aqueous polyurethane dispersionsPublication . Fernandes, Isabel P.; Barreiro, M.F.; Costa, M.R.N.The industrial production of aqueous polyurethane dispersions (PUDs) is nowadays a well established technology. There are two main synthetic routes to produce PUDs: the acetone process (a former process developed by Bayer AG) and the pre-polymer process (developed as an alternative response to the patented acetone process). Comparatively to the acetone process, the pre-polymer process has one major advantage since it requires none or only small amounts of acetone. The pre-polymer process, at present, is being forced to readapt due to ongoing developments, partly motivated by process constraints, raw materials restrictions and the need to obtain a true solvent-free product. Allied to this fact it is worth mentioning the European REACH legislation, which is having a considerable influence on the PUD industry. Most of the industrially produced PUDs use dimethylol propionic acid (DMPA) as the internal emulsifier. DMPA is sparingly soluble in the reactive mixture and needs to be previously dissolved in an organic solvent, usually Nmethyl- 2-pyrrolidone (NMP). NMP is difficult to remove and will remain in the final product. There are some alternatives to achieve the NMP-free concept. Among them we can refer the direct NM P replacement by an equivalent solvent, the DMPA replacement by an equivalent hydrophilising diol but with better solubility in the reactive mixture and the preneutralization of DMPA prior to reaction with isocyanate.
- Solvent-free aqueous polyurethane dispersionsPublication . Fernandes, Isabel P.; Barreiro, M.F.; Costa, M.R.N.The industrial production of aqueous polyurethane dispersions (PUDs) is nowadays a well established technology. There are two main synthetic routes to produce PUDs: the acetone process (a former process developed by Bayer AG) and the pre-polymer process (developed as an alternative response to the patented acetone process). Comparatively to the acetone process, the pre-polymer process has one major advantage since it requires none or only small amounts of acetone. The pre-polymer process, at present, is being forced to readapt due to ongoing developments, partly motivated by process constraints, raw materials restrictions and the need to obtain a true solvent-free product. Allied to this fact it is worth mentioning the European REACH legislation, which is having a considerable influence on the PUD industry. Most of the industrially produced PUDs use dimethylol propionic acid (DMPA) as the internal emulsifier. DMPA is sparingly soluble in the reactive mixture and needs to be previously dissolved in an organic solvent, usually Nmethyl- 2-pyrrolidone (NMP). NMP is difficult to remove and will remain in the final product. There are some alternatives to achieve the NMP-free concept. Among them we can refer the direct NM P replacement by an equivalent solvent, the DMPA replacement by an equivalent hydrophilising diol but with better solubility in the reactive mixture and the preneutralization of DMPA prior to reaction with isocyanates.
- Study of the formation of a segmented polyester-polyurethanePublication . Barreiro, M.F.; Costa, M.R.N.Segmented polyurethanes are block copolymers of the (AB)n type characterized by a microphase-separated morphology. They are an important subclass of the family of thermoplastic elastomers presenting a broad range of applications, including adhesives and coatings. Typically, phase separation can go along with polymerization, being of great importance the simultaneous study of these two phenomena. In this work the development of a methodology for the study of the formation of a segmented polyester-polyurethane is presented. In a first stage, the determination through FTIR in ATR mode of the kinetics and phase separation has been undertaken. In a second step, the experimental size distributions of hard segments, by an original selective hydrolysis procedure was carried out. The polyurethanes have been prepared starting with 4,4’-methylene-diphenylene diisocyanate (MDI), policaprolactone diol (PCL) and 1,4-butanediol (BD) as chain extender, at various initial mole ratios. Along the polymerization, the system has typically presented a transition from a homogeneous state, during which the chemical kinetics was well described by an overall second order law, into a system presenting phase separation. The critical point, where phase separation starts, was characterized in terms of isocyanate conversion and number and weight average hard segments sizes. It became clear that phase separation requires not only a certain lower bound of the average hard segment size but also at least some minimum value of the concentration of hard segments. The occurrence of phase separation along the formation reaction modifies the size distribution of hard segments with respect to the geometrical distribution prevailing at homogeneous conditions. Moreover, average size tends to decrease as a consequence of phase segregation.
- Water-based polyurethane dispersions: chemistry, technology and applicationsPublication . Fernandes, Isabel P.; Costa, M.R.N.; Ferreira, Maria José; Barreiro, M.F.Over the past few decades, polyurethane-polyurea aqueous dispersions (PUDs) have developed a solid reputation for high performance applications, particularly in the field of adhesives and coatings. PUDs are mostly environmentally compatible products; they are totally devoid or contain only low amounts of volatile organic compounds (VOC). This is an important feature in view of the present environmental policies where governments and internal agencies are placing emphasis on developing sustainable processes, improving work conditions and reducing emissions of toxic and polluting substances into the atmosphere. In the past years, our research group has been involved in the development of polyurethane-polyurea aqueous dispersions for two main applications (footwear and indirect food contact). With this work we intend to review this theme and describe some of the achieved developments. Characterization of commercial dispersions will be presented and examples of synthesis will be described, following a modified pre-polymer process developed in our group.