Plant Oil-Based Waterborne Polyurethanes: A Brief Review

The increasing pressure from consumers and policy makers to reduce the use of synthetic polymers,whose production contributes to the depletion of non-renewable resources and are usually non-biodegradable,has prompted the efforts to find suitable bio-based sources for the production of polymers.Vegetable oils have been a frequently spotted in this search because they are versatile,highly available and a low cost liquid biosource,which can be used in the synthesis of a wide plethora of different polymers and reactive monomers.Following the same idea of reducing the environmental stress,the traditional polyurethanes that are soluble in organic solvents have been targeted for replacement,particularly in applications such as adhesives and coatings,in which the solvent is released to the atmosphere increasing the air pollution.Instead,waterborne polyurethanes(WBPU),which are polyurethane dispersions(PUD)prepared in aqueous media,release benign water to the atmosphere during use as supported or self-standing films for different applications.In this brief review,the contributions to the development of WBPUs based on vegetable oils are discussed,focusing mainly on the contributions of the last decade.The synthesis of ionic and nonionic PUDs,their characterization and the properties of the resulting dried materials,as well as derived composite materials are considered.

Polyurethane Composites Synthesized Using Natural Oil-Based Polyols and Sisal Fibe

Elastomeric polyurethanes were prepared from a reference polyurethane system modified with biobased polyols synthesized using rapeseed or palm oils.The reference material was modified by replacement of the commercial polyol by 10%of biopolyols and also by addition of sisal fibers up to 5 wt%.The higher functionality of the biopolyols increased the crosslinking density of the networks and this was reflected by an increase in hardness and a decrease in water absorption.The effect of the sisal fibers mainly improved the mechanical and thermomechanical properties of the system with rapeseed oil because of good dispersion and strong fiber-matrix interaction.The system containing palm oil polyol corresponded to an initial formulation of high viscosity and,consequently,the resulting composites presented lower densities than the theoretically expected ones.These results are associated with fiber dispersion problems in the initial reactive mixture.

Liquefaction of Kraft Lignin at Atmospheric Pressure

Kraft lignin was liquefied using polyethylene glycol#400(PEG)and glycerol(G)in a weight ratio of 80/20(w/w)and sulphuric acid(SA)as catalyst under atmospheric pressure at 160ºC.The three independent variables:reaction time(60,80 and 100 min),percentage of lignin(15,20 and 25%,w/w),and catalyst concentration(0,3 and 6%,w/w),were varied resulting in 27 experimental runs.The effect of these reaction conditions on the properties of the polyols was evaluated.The statistical analysis showed that only“the percentage of lignin”did not influence the properties of the liquefied products,however,reaction time and catalyst load were important parameters.The resulting liquefied products were characterized by FTIR analysis.

Liquefaction of corn stover using industrial biodiesel glycerol

Corn stover was liquefied using an industrial biodiesel glycerol as a liquefying agent at atmospheric pressure and low temperature.It was found that the liquefaction yield increased with increasing glycerol-to-corn stover ratios.Sulfuric acid,added as a catalyst,was found to improve liquefaction yield.The hydroxyl number,moisture content,acid number,pH value,viscosity,density,elemental composition,and higher heating value of the liquefied corn stover samples were determined.The liquefied corn stover showed a high hydroxyl number of 270-310 mg KOH/g.Fourier transform infrared spectroscopy(FTIR)results revealed the functional groups and confirmed the existence of the OH group in the liquefied corn stover,indicating that the liquefied corn stover is indeed a source of polyols and a potential chemical stock for the synthesis of polymers.