Polyurethane Dispersion

Excerpt: Inorder to avoid fossil based hazardous environmental polluting solvent coating system, several polyols wERE prepared fROm different renewable sources such as soybean oil

Abstract

Inorder to avoid fossil based hazardous environmental polluting solvent coating system, several polyols wERE prepared fROm different renewable sources such as soybean oil and jatropha oil to synthesis polyurethane resin which is then used in water based polyurethane dispersion formulations. In this coating system water is used as dispersing medium, drying of the film takes place by evaporation of water followed by coalescence of molecules which would result in environmental friendly coating system which offers better mechanical and chemical properties.

Introduction

POLYURETHANE (PU) has find application in wide area such as adhesives, sealant, coating and fibers due its good weathering and its mechanical properties. But polyurethane has one major problem that is, it requires environmental pollutant. Solvent like methyl ethyl ketone and acetone to enhance easy process ability, in order to overcome this problem dispersibility of polyurethane into the water is improved by modifying the backbone Chain using ionic substance which will act as a. Nowadays polyurethane dispersion (PUDs) replaces many of the solvent based coating system, because dispersing medium used here is water, which does not emit any hazardous gas to the environment. Film drying on the substrate takes place by evaporation of water followed by molecular coalescence. PUDs were quit costlier as compared to that of solvent based coating system, but cost can be reduced by blending it with low cost acrylic emulsion. The main aim of this paper is to provide overview of the latest polyurethane dispersion technologies which were obtained from renewable resources such as jatropha oil and soy bean oil.

Generally Polyurethane is a condensation product of polyol (Usually polyester polyol) and di isosyanate (this reaction follows inter molecular rearrangement mechanism). Synthesized oligomeric PU resin has high viscosity, in order to reduce the viscosity and improve the process ability acetone (diluents) should be added into the resin system. Then the ionic compound such as sulfonates is introduced on the backbone of the resin as a pendant which will be responsible for the resin-water compatibilization .Finally acetone is removed from the medium through distillation process. Film drying is achieved by two ways one is happen by evaporation of water followed by coalescences of molecules present in the resin, this phenomenon is called as physical drying, which is actually a single pack system (1K system) and another way is by using isocyanides hardener to dry the film through chemical cross-linking which is called as two pack system (2K system), this phenomenon is called as crystallization which gives required bond strength.

Polyol synthesized from Jatropha Oil (JOL)

Sariah Saalah and et al [1] were synthesized polyol (with different hydroxyl numbers in mg KOH/g) from jatropha oil, PU obtained from this polyol assures a combination of physical properties such high elongation, tear strength and abrasion resistance. Environmentally friendly waterborne polyurethane dispersions have been synthesized from jatropha oil-based polyols and isophrene diisocyanate IPDI.

Epoxidized jatropha oil intermediate was prepared by reacting JOL with formic acid and hydrogen peroxide; intermediate produced is washed with distilled water to remove the remaining acids. Jatropha oil based polyol is prepared by reacting required proportion of methanol and water in presence of sulphuric acid at 64°C, then in the prepared epoxidized jatropha oil was added drop wise into the reaction mixture and sodium bicarbonate was added to quench the reaction. Quenching process reduce the system temperature still to the room temperature medium present in the system is removed by vacuum distillation at elevated temperature. JOL in methyl ethyl ketone was reacted with dimethylol propionic acid(DMPA acts as an emulsifier or suspension stabilized) at 80°C. Isoprene diisocyanide were added drop wise into the reaction medium and left the reaction system for 3hrs without disturbance, 2-hydroxyethyl methacrylate were added until NCO get consumed (which can be determined by FTIR). Finally reaction medium is allowed to cool, neutralized with triethyl amine and solvent ethyl methyl ketone was removed by vacuum distillation. Prepared PU dispersion was characterized by using ATR-FTIR. The resulting JPU coating films exhibited elastomeric polymer characteristics with a Young's modulus ranging from 1 to 28 MPa, a tensile strength of 1.8 to 4.0 MPa and elongation at break ranging from 85 to 325%.

Polyol prepared from Soybean-Oil

Yongshang Lu and et al [1] have synthesized polyol from soybean oil which is a renewable source. The unsaturated site present in the soybean oil is reacted with required amount of formic acid and hydrogen peroxide in vigorous stirring condition at room temperature for 24hrs which results in epoxidized soybean oil (ESO) and it was characterized by 'H-NMR spectroscopy. Then prepared ESO was reacted with methanol to produce methoxylated soybean oil polyol(MSOL), then the resultant product was washed using mixture consisting of methanol, water, isopropanol and fluoroboric acid. Then MSOL is made to reacted with Isophorone diisocyanate (IPDI) and dimethylol propionic acid (DMPA) in a Methyl ethyl ketone peroxide (MEK) solvent medium at elevated temperature, this results in the formation of polyurethane (PU) resin. Finally polyurethane is dispersed in distilled water to prepare a Soybean polyurethane dispersion and diluent medium present in the system is removed from it. 20% solids coating can be achieved from this synthesis method. The present study was characterized using FTIR, NMR, Transmission electron microscopy (TEM), Thermo gravimetric Analysis (TGA) and DMTA etc.

Polyol prepared from the vegetable oil has more number of hydroxyl groups, so the monomer which involves in the reaction exhibits polyfunctionality. Polyol (polyfunctional ranging from 2.4 to 4.0) increase the cross link density of polyurethane and results in polymer with high thermal resistance and nechanical properties such as tensile strength from 7.6 to 13 MPa, and toughness from 13.6 to 27 MPa.

Conclusion

Solvent free bio based polyurethane dispersion was synthesized from renewable sources (from Soybean oil and jatropha oil) which gives extensive mechanical and thermal properties as compared to the conventional polyurethane synthesized from fossil non renewable source. Advantage of using this type of renewable source is to produce polymer with high cross link density which intern provides higher performance (by providing a good thermal, mechanical, and better processabilty) in an environment friendly manner.

References

  1. https://adhesives.specialchem.com/selection- guide/polyurethane-dispersions-state-of-the-art/polyurethane-dispersion-chemistry
  2. https://doi.org/10.1016/j.indcrop.2014.10.046 Waterborne polyurethane dispersions synthesized from jatropha oil, journal name: Industrial Crops and Products, Sariah Saalah and et al [1],
  3. http://pubs.acs.org/doi/pdfplus/10.1021/bm801030g Soybean-Oil-Based Waterborne Polyurethane Dispersions: Effects of Polyol Functionality and Hard Segment Content on Properties,Biomacromolecules 2008, 9, 3332–3340 Yongshang Lu et al [2]

Author Details

Jeganathan.R

Department of Polymer and Surface Technology,

Institute of Chemical Technology

Mumbai- 400 019