Hydrolysable Chestnut Tannin Extract Chemical Complexity in Its Reactions for Non-Isocyanate Polyurethanes(NIPU)Foams

Non-isocyanate polyurethane(NIPU)foams from a commercial hydrolysable tannin extract,chestnut wood tannin extract,have been prepared to determine what chemical species and products are taking part in the reactions involved.This method is based on two main steps:the reaction with dimethyl carbonate and the formation of urethane bonds by further reaction of the carbonated tannin with a diamine-like hexamethylene diamine.The hydroxyl groups on the tannin polyphenols and on the carbohydrates intimately linked with it and part of a hydrolysable tannin are the groups involved in these reactions.The carbohydrate skeleton of the hydrolysable tannin is also able to participate through its hydroxyl groups to the same two reactions rendering the whole molecular complex able to react to form NIPUs.The analysis by Matrix-Assisted Laser Desorption Ionization(MALDI-TOF)mass spectrometry and 13C Nuclear Magnetic Resonance(13C NMR)to further investigate the reaction mechanisms involved revealed the unsuspected complexity of chestnut hydrolysable tannin,with different fragments reacting in different manners forming a hardened network of considerable complexity.As the morphology and performance of these types of foams changes slightly with the change in the amount of glutaraldehyde and hexamine hardeners,the best performing foam formulation previously determined was scanned by SEM and analysed chemically for the structures formed.

Modification of Wood by Tannin-Furfuryl Alcohol Resins-Effect on Dimensional Stability,Mechanical Properties and Decay Durability

Furfurylation is a well-known wood modification technology.This paper studied the effect of tannin addition on the wood furfurylation.Three kinds of dicarboxylic acids,adipic acid,succinic acid,and tartaric acid,as well as glyoxal as a comparing agent,were used to catalyse the polymerisation of furanic or tannin-furanic solutions during wood modification.Impregnation of furanic or tannin-furanic solution at a certain concentration into the wood followed with curing at 103℃for a specific duration was performed for the wood modification.Different properties of the modified woods like dimensional stability,resistance of treatment to leaching,mechanical properties,decay durability against white-rot(Coriolus versicolor,Pycnoporus sanguineus)and brown-rot(Coniophora puteana)as well as their chemical and anatomical characteristics were evaluated.Results revealed that the partial substitution of FA by the tannins improved the fixation of the chemicals impregnated in wood.Further,dimensional stability,leaching resistance,Brinell hardness,modulus of elasticity/modulus of rupture,and decay durability properties of the furfurylated wood were also improved in the presence of tannins.Scanning electron microscopy revealed the deposition of the polymer in the wood lumen cells and in the wood cell walls.

Flexible Biofoams Based on Furanics and Fatty Acids Esterified Tannin

Water repellant,flexible biofoams using tannin esterified with various fatty acid chains,namely lauric,palmitic and oleic acids,by reaction with lauryl chloride,palmitoyl chloride,and oleyl chloride were developed and their characteristics compared with the equivalently esterified rigid biofoams.Glycerol,while initially added to control the reaction temperature,was used as a plasticizer yielding flexible biofoams presenting the same water repellant character that the equivalent rigid foams.Acetaldehyde was used as the cross-linking agent instead of formaldehyde,as it showed a better performance with the esterified tannin.The compression results showed a significant decrease of the Modulus of Elasticity(MOE)of the flexible foams in relation to that of the rigid foams,confirming their flexible character.The lauryl-and palmitoyl-esterified biofoams presented similar mechanical properties,while the oleyl-esterified biofoam presented different mechanical and morphological result not really showing the expected flexibility.Both the esterified rigid and flexible tannin-based biofoams showed good water resistance and their sessile drop contact angle analysis as a function of time confirmed this characteristic.Scanning Electron Microscope(SEM)analysis showed the flexible foams to present a higher proportion of closed cells than the rigid foams.Conversely,the cells depth of the flexible foams was lower than that of the rigid foam.As regards their thermal resistance,the flexible foams showed a slight loss of mass compared to the rigid ones without glycerol.Both types of foams presented much lower surface friability of non-esterified rigid foams.

Self-Blowing Non-Isocyanate Polyurethane Foams Based on Hydrolysable Tannins

ABSTRACT Non-isocyanate polyurethane(NIPU)foams using a hydrolysable tannin,also vulgarly called tannic acid,namely here commercial chestnut wood tannin extract was prepared.Compression strength did not appear to depend on the foam apparent density while the formulation composition of the NIPU foams has been shown to be more determinant.These NIPU foams appeared to be self-extinguishing once the high temperature flame is removed.The ignition time gave encouraging results but for improved fire resistance the foams may need some fire-retardant addition.FTIR spectrometry showed the formation of non-isocyanate urethane linkages.Thermogravimetric analysis indicated a good thermal resistance of these foams,with thermal degradation following four phases.First in the interval 25℃–120℃ range,mainly evaporation of water occurs with a maximal loss of 10%weight.In the 150℃–450℃ temperature range foams mass loss is of almost 70%.In particular in the 125℃–275℃ range occurs the degradation of some small molecular weight substances.In the 500℃–790℃ temperature range the foams do not present any further large degradation.