MALDI ToF Investigation of the Reaction of Soy Protein Isolate with Glutaraldehyde for Wood Adhesives

Soy protein adhesives are currently a hot research topic in the wood panels industry for the abundant raw material reserves,reasonable price and outstanding environmental features.But their poor water resistance,low bonding strength and intolerance to mold are major drawbacks,so that proper modification before use is essential.Glutaraldehyde is one of the more apt cross-linking agents for soybean protein adhesives,which can effectively improve the bonding strength and water resistance of the adhesive.Equally,glutaraldehyde is also an efficient and broad-spectrum fungicide that can significantly improve the anti-fungal properties of a soy protein adhesive.In the work presented here,matrix assisted laser desorption ionization(MALDI-ToF)mass spectrometry and Fourier transform infrared spectroscopy techniques were used to analyze the reaction mechanism of glutaraldehyde cross-linking soybean protein.The results confirmed the reaction of the aldehyde group with amino groups of the side chains and the amide groups of the peptide linkages constituting the skeletal chain of the protein.The laboratory plywood and particleboard bonded with glutaraldehyde-soy bean protein adhesives were prepared to determine the adhesive bonding properties,the dry strength,24 h cold water soaking wet strength and 3 h hot water(63°C)wet strength of plywood were 2.03,1.13 and 0.75 MPa,respectively,which satisfied the requirements of industrial production.

A Review of Soy-Tannin Gelling for Resins Applications

Soy flour(SF),soy protein and soy protein isolates(SPI)have been the focus of increasing research on their application as new materials for a variety of applications,mainly for wood adhesives and other resins.Tannins too have been the focus of increasing research for similar applications.While both materials are classed as non-toxic and have achieved interesting results the majority of the numerous and rather inventive approaches have still relied on some sort of hardeners or cross-linkers to bring either of them or even their combination to achieve acceptable results.The paper after a presentation of the two materials and their characteristics concentrates on the formation of gels,gelling and even hardening in the case of soy-tannin combined resins.The chapter than finishes with details of the formation of resins giving suitable wood adhesive of acceptable performance by the covalent coreaction of soy protein and tannin without any other hardener,thus totally bio-sourced,non-toxic and environment friendly as a base of further advances to expect in future by these two materials combination.

Self-Cross-Linked Tannin-Aminated Tannin Surface Coatings for Particleboard

Aminated tannins were prepared by reacting mimosa condensed tannin extract with ammonia yielding the substitution of many,if not all of the tannin hydroxyl groups with–NH_(2)groups.A tannin-aminated tannin(ATT)particleboard coating was then prepared by reacting raw tannin extract with aminated tannin extract and thus cross-linking the two by substituting tannin’s hydroxyl groups with the–NH_(2)groups on the aminated tannin to form–NH-bridges between the two.The resulting particleboard coating gave encouraging results when pressed at 180℃for 3 min.Conversely,the system in which tannin was reacted/cross-liked with urea(ATU)by a similar amination reaction did not perform as well as the ATT system,and this even when a higher curing temperature and longer hot press time were used.In particular its water repellence was worse probably due to the presence of urea and such a system with lower reactivity.Nonetheless,substituting the tannin–OHs with the urea–NH_(2)groups appeared to also take place.ATT gave better results than ATU as regards water repellence and mechanical resistance as shown by the cross cut test.The ATT system was shown to be between 95%and 98%biosourced.The difference appeared to be due,by TMA analysis,to the much faster formation of the ATT hardened network leading to a better cross-linked polymer coating.The chemical species formed for both the ATT and ATU system were studied by MALDI ToF and CP MAS^(13)C NMR.

A Melamine–Dialdehyde Starch Wood Particleboard Surface Finish without Formaldehyde

Melamine-dialdehyde starch resins used for wood surface finishes have been developed.The reaction of melamine with dialdehyde starch has been shown to occur by FTIR and MALDI ToF spectrometry,with several oligomer species due to the reaction of the two materials being identified,and the resin thermal stability was studied by thermogravimetric analysis.The resins were prepared by two different procedures when it was realized that dialdehyde starch is sensitive to too high a temperature for prolonged times.The melamine-dialdehyde starch resins were applied on particleboard supports as a direct liquid surface finish and a resin-impregnated paper.The surface finishes were tested for adhesion by the cross-cut test,their initial sessile drop contact angle,and the contact angle evolution as a function of time.The best results were obtained by the resins catalyzed by 2% ammonium sulfate and applied to the support surface as a resin-impregnated paper hot pressed for 3 min at 200℃,although the results at 180℃ also looked promising.

MUF Resins Improved by Citric Acid as Adhesives for Wood Veneer Panels

This article presents the first applied results of using citric acid in combinations with a melamine-urea-formal-dehyde(MUF)resin for bonding wood veneers.The chemical reactions involved are shown based on a MALDI ToF analysis of the reaction of the MUF resin with citric acid.The preliminary results of the physical and mechanical properties of the LVL prepared are also presented.Veneers from Populus sp were used to manufacture 5-layer laminated veneer lumber(LVL)of small dimensions.Five combinations of the amount of citric acid,MUF spread rate and pressing parameters were tested.LVL bonded with 20%of citric acid+100 g/m^(2)of MUF,hot-pressed using a 3-step process with maximum 1.5 MPa of pressure yielded the board with better dimensional stability and mechanical properties.It could be concluded that citric acid in combination with MUF can be used for bonding wood veneer and the research should be continued to study further the parameters involved and to enhance the results.

Tannin-Based Biofoams-A Review

This review details the development of tannin-based biofoams for fire resistance and acoustic insulation and details the different varieties of these foams that have been developed,from tannin-furanic self-blowing foams to tannin-furanic polyurethanes and finally non-isocyanate tannin-basedcarbohydrates polyurethanes(NIPU).

Organosolv Lignin for Non-Isocyanate Based Polyurethanes (NIPU) as Wood Adhesive

A non-isocyanate-based polyurethane(NIPU)wood adhesive was produced from organosolv lignin,which is a bio-sourced raw material,available in large quantities and produced as a by-product of the paper industry.The formulation of this new lignin-based NIPU adhesive,which is presented,was chemically characterised by Matrix-Assisted Laser Desorption Ionization Time of Flight(MALDI ToF)mass spectrometry and by Fourier Transform Infra-Red(FTIR)spectrometry analyses.The oligomers formed were determined and showed that the three species involved in the NIPU adhesive preparation were formed by the co-reaction of the three reagents used:lignin,dimethyl carbonate,and hexamethylene diamine.Linear and branched structures were both identi-fied.Mechanical properties of the adhesive were determined using the Automated Bonding Evaluation System(ABES)and internal bond(IB)strength test of the laboratory particleboard bonded with it.The adhesive has shown satisfactory mechanical properties after hot pressing at 230℃.Such a temperature is used industrially in the most modern particleboard factories,but since it is hardly feasible for more conventional wood bonding equipment,the reactivity of the NIPU adhesive was successfully increased with the addition of a small percentage of a silane coupling agent.With the addition of the silane,the proposed NIPU adhesive could also be used at a hot-pressing temperature lower than 200℃.

Covalent and Ionic Bonding between Tannin and Collagen in Leather Making and Shrinking:A MALDI-ToF Study

Collagen powder hydrolysates were reacted with a solution of commercial mimosa bark tannin extract.The mixture was prepared at ambient temperature and prepared at 80°C to determine what reactions,if any,did occur between the collagen protein through its amino acids and the polyphenolic condensed tannin.The reaction products obtained were analyzed by matrix assisted laser desorption ionization time-of-flight(MALDI ToF)mass spectrometry.Reactions between the two materials did appear to occur,with the formation of a relatively small proportion of covalent and ionic linkages at ambient temperature but a considerable proportion of covalent linkages tannin-protein amino acids and the disappearance of ionic bonds.The linkages between the two materials appeared to be by amination of the phenolic–OHs of the tannin by the amino groups of the non-skeletal side chains of arginine,and by esterification by the–COOH groups of glutamic and aspartic acid of the aliphatic alcohol-OH on the C3 site of the flavonoid units heterocycle of the tannin.The proportion of covalent linkages increases markedly and predominate with increasing temperatures.This tightening of the tannin-protein covalent network formed may be an additional contributing factor both to leather wear resistance and performance as well to leather shrinking when this is subjected to excessive temperatures.

Curing Kinetics of Tannin and Lignin Biobased Adhesives Determined by DSC and ABES

The curing process of two biobased adhesives:pine tanninhexamine(TH)and organosolv lignin non-isocyanate polyurethane(NIPU),suitable for interior nonstructural use,were compared with commercial urea-formaldehyde(UF)adhesive.Changes in chemical structure before and after the curing process were observed with Fouriertransform infrared spectroscopy(FTIR).The process of adhesive curing was monitored with differential scanning calorimetry(DSC)and the automated bonding evaluation system(ABES).Both DSC and ABES measurements confirmed UF as the fastest and NIPU as the slowest curing adhesive observed.Taking into account the ABES results,the optimal pressing parameters for the TH adhesive would be 4 min at 175℃,for the NIPU adhesive 7 min at 200℃and for the UF 1.5 min at 100℃.Strong linear correlation was observed between mechanical and chemical curing for the UF and NIPU adhesives,whereas lower correlation was observed for the TH adhesive.At all observed adhesives,the DSC measurements were underestimating the curing process determined by ABES in the first part and overestimating it at the end.The underestimation was the most evident with the TH adhesive and the less with the UF adhesive.When comparing the uncured and cured FTIR spectra of all three types of adhesives,a drastic decrease in the characteristic band of-OH groups at 3330–3400 cm^(−1)and an increase in the signal intensity at 2920 cm^(−1)of aliphatic-CH2-groups were observed.For the UF adhesive,the C=O stretching frequency has shifted from 1632 cm^(−1)for uncured to three different bands at 1766,1701,and 1655 cm^(−1)for cured UF.The sharp band for phenolic alcohols at 1236 cm^(−1)of C–O stretch and hydroxyl O–H functional group at 1009 cm^(−1)and at 684 cm^(−1)of uncured TH adhesive diminished during curing,which indicates that a crosslinking reaction occurs via-OH groups.The peak of the C=O group of urethane bridges at 1697 cm^(−1)for uncured NIPU shifted to lower wavenumber at 1633 cm^(−1)for cured NIPU.

No-Aldehydes Glucose/Sucrose-Triacetin-Diamine Wood Adhesives for Particleboard

A three reagents adhesive system for wood particleboards not containing any aldehyde was developed by the reaction of glucose or sucrose with triacetin(glycerin triacetate)and with hexamethylene diamine.The system was found to be based on the mix of three reactions,namely the reaction of(i)glucose with triacetin,(ii)of the diamine with triacetin,and(iii)of glucose with the diamine.The chemical species formed were identified by Matrix Assisted Laser Desorption Ionization Time of Flight(MALDI-ToF)mass spectrometry.Wood particleboard panels were prepared with this adhesive system and gave good internal bond(IB)strength results suitable for interior grade panels and with extremely low formaldehyde emission.

Glucose-Biobased Non-Isocyanate Polyurethane Rigid Foams

Glucose-based non-isocyanate polyurethanes(NIPU)were prepared by reaction of glucose with dimethyl carbonate and hexamethylene diamine.These were used to prepare partially biobased polyurethane foams by reaction with NaHCO3 as a blowing agent and addition of a silane coupling agent having different functions such as coreactant and adjuvant to obtain more uniform and smaller cells.The foams were foamed and hardened by applying heat.The foams presented very limited fire resistance indicating that as for synthetic polyurethane foams the eventual use of a fire retardant appears to be necessary.The 2 hours water absorption was used to indicate if close cells or open cells occur.More characteristic is their stress strain behaviour.While compression does indeed flatten the cell walls nonetheless the cellular structure is maintained and the cell walls have not been destroyed.This indicates a certain level of elasticity in the cell walls of formulations containing NaHCO3.In effect the macro-appearance of this foams,confirms this explanation as the foam is densified and holds together.

The Use of Aloe vera as Natural Coagulant in Algerian Drinking Water Treatment Plant

The purpose of this work is the study the ability of the plant material Aloe vera to act as natural coagulant using raw water obtained from a drinking water treatment plant(Mila,Algeria).Different solvents such as:NaCl;NaOH and HCl were used as chemical activators to extract the active components from the Aloe vera plant,and different coagulation-flocculation experiments were conducted in a jar test apparatus to evaluate the perfor-mance of the extracted coagulant.Also,the effect of coagulant dose on some water parameters such as turbidity,pH,total alkalinity and organic matter were investigated.The results showed that the use of coagulants obtained by using different solvents increases the coagulation efficiency compared to the coagulant obtained from the raw material,for example the maximum turbidity removal efficiency was 28.23,78.07,83.46 and 85.15%when using powdered Aloe vera(raw material),AV-NaCl(0.5 M),AV-NaOH(0.05 M)and AV-HCl(0.05 M),respectively.The results defined,that the residual turbidity obtained in this work,where the Aloe vera was used(after treat-ment by solvents)produced a turbidity lower than the Algerian standard(5 NTU)with initial turbidity(13 NTU).In this study,the infrared spectrum study and analysis has revealed the presence of different functional groups,which are responsible for the coagulation process.

Desorption Behavior and Thermogravimetric Analysis of Bio-Hardeners

In this work,the thermal degradation and drying of bio-hardeners are investigated.Four bio-hardeners based on exudates of Senegalia senegal,Vachellia nilotica,Vachellia seyal,and Acacia siebteriana were analyzed by FTIR and thermogravimetric analysis,and a desorption study was also conducted.The analysis by infrared spectroscopy indicates the existence of oligomers of different types all giving 5-hydroxy-2-hydroxymethylfuran and 2,5-dihydroxymethylfuran which are then the real hardening molecules.The pyrolysis of these extracts reveals three main regions of mass loss,a first region is located between 25℃and 110℃reflecting the loss of water from the adhesive and the formation of some traces of volatile organic compounds such as CO_(2)and CO,a second zone characterized by the release of CO,CO_(2)and CH4 gases with peaks between 110°and 798.8℃.At the end of the analysis,about 22%of the initial mass remains undecomposed,this mass corresponds to the rigid segments of the bio-hardener which are not completely decomposed.