Preparation of Environmentally Friendly Urea-Hexanediamine-Glyoxal(HUG)Resin Wood Adhesive

Using non-toxic,low-volatile glyoxal to completely replace formaldehyde for preparing urea-glyoxal(UG)resin adhesive is a hot research topic that could be of great interest for the wood industry.However,urea-glyoxal(UG)resins prepared by just using glyoxal instead of formaldehyde usually yields a lower degree of polymerization.This results in a poorer bonding performance and water resistance of UG resins.A good solution is to pre-react urea to preform polyurea molecules presenting already a certain degree of polymerization,and then to condense these with glyoxal to obtain a novel UG resin.Therefore,in this present work,the urea was reacted with hexamethylene diamine to form a polyurea named HU,and then this was used to react it with different amounts of glyoxal to synthesize hexamethylenediamine-urea-glyoxal(HUG)polycondensation resins,and to use this for bonding plywood.The results show that the glyoxal can well react with HU polyuria via addition and schiff base reaction,and also the HUG resin exhibits excellent bonding strength and water resistance.The shear strength of the plywood bonded with this HUG at 160°C hot press temperature as high as 1.93 MPa,2.16 MPa and 1.61 MPa,respectively,which meets the requirement of the China national standard GB/T 9846-2015(≥0.7 MPa),and can be a good choice as a wood adhesive for industrial application.

Synthesis, performance and structure characterization of glyoxal-monomethylolurea-melamine (G-MMU-M) co-condensed resin

In order to reduce the formaldehyde emission of formaldehyde-based wood adhesive from the source,it is aimed to develop a novel co-condensed resin of glyoxal-monomethylolurea-melamine(G-MMU-M).A series of G-MMU-M resins with various formulations of raw materials were successfully prepared.The basic properties and bonding performance of the G-MMU-M resins were determined.Furthermore,the structures of resins were characterized by FTIR,^(13)C NMR,XPS,and ESI-MS.The results show that the prepared G-MMU-M resin remains stable for 30 d,meanwhile,the dry and wet bonding strength of the plywoods bonded with the resins,solid content and viscosity are influenced greatly by the addition amount of melamine and MMU/G molar ratio.The G-MMU-M resins with MMU/G molar ratio of 0.9:1.0 and 8% melamine exhibit the highest dry and bonding strength of 1.98 MPa and 1.27 MPa,increased by 34% and 63%,respectively,in comparison with glyoxal-monomethylolurea(G-MMU)resin.In the G-MMU-M resins,there were four main oligomers including M—CH(—^(+)CH-MMU)-O-MMU,M-CH(—CH_(2)OH)-MMU-O-MMU,M—CH(—OH)—^(+)CH-MMU-O-MMU,and M—CH(—^(+)CH-MMU)-MMU-p-G.

The Study on Bamboo Microfibers Isolated by Steam Explosion and Their Comprehensive Properties

To overcome the shortage of wood resources as well as to develop novel natural fibers materials,the Chimonobambusa quadrangularis(CQ)and Qiongzhuea tumidinoda(QT)planted in Southwest China were effectively isolated by the steam explosion(SE).The fine and uniform bamboo microfibers derived from CQ and QT were obtained,and their smallest average widths were 12.62μm and 16.05μm,respectively.The effects of steam explosion on the micro-morphology,chemical composition,thermal stability,crystallinity,surface wettability,and mechanical properties of bamboo microfibers were comprehensively investigated.The results showed that the relative content of cellulose in bamboo microfibers increased but the hemicellulose and lignin contents decreased after SE.The degrees of crystallinity for CQ and QT increased from 40.49%and 39.46%to 68.90%and 55.78%,respectively.The thermal stability and surface hydrophilicity were also improved.The CQ microfibers had a maximum decomposition temperature of 2.79°C,a tensile strength of 58.54 MPa,an elongation at break of 0.6%,and a water contact angle of 2.7°higher than those of the QT microfibers.

Preparation of Film Based on Polyvinyl Alcohol Modified by Alkaline Starch and Lignin Fiber

This study presents an easily prepared film based on alkaline starch-polyvinyl alcohol hybrid and lignin fiber as an additive(SPL film).The SPL film was prepared under acidic conditions through a polycondensation reaction of PVA and a mixture incorporating alkaline starch and lignin fiber from agriculture or forest source.The examination using scanning electron microscopy(SEM)showed that the surface of SPL film was smooth and the lignin fiber had good compatibility within the film hybrid.Electrospray ionization mass spectroscopy(ESI-MS)and fourier transform infrared(FTIR)investigations indicated that alkaline starch and lignin fiber reacted with PVA under acidic conditions and that–CH_(2)–O–groups were involved in the cross-linking of the SPL system.In addition,the SPL film exhibited only 4%light transmittance,which effectively reduces the ultraviolet and visible light(UV-Vis)penetration,along with good performance when exposed to thermal degradation,in which the mass loss reached around 60%at 400℃.More-over,the SPL film acquired excellent tensile strength,which is much higher than that of PVA-lignin(PL)composite film.

脲基超支化聚合物木材胶黏剂的合成与性能

脲基通常由异氰酸酯与氨基反应产生,由于异氰酸酯对人体健康和环境具有较大的危害且成本较高,因此利用低成本的尿素替代异氰酸酯合成脲基聚合物胶黏剂的途径正越来越受到关注。文中利用廉价的丙烯酸甲酯和对苯二胺为原料,通过迈克尔加成反应和酰胺化反应合成了树枝状四元胺,再与尿素在无催化剂和无溶剂的条件下进行A_(2)+B_(4)熔融缩聚,得到一系列低成本无醛的超支化脲基聚合物胶黏剂。利用核磁共振、红外光谱、质谱、凝胶渗透色谱等方法验证了其结构;差示扫描量热分析和热重分析表征了其热行为和热稳定性。最后将该脲基聚合物作为胶黏剂黏接不同基材,结果表明,粘接木材的剪切强度大于1.34MPa,远远高于GB/T17657-2013对II类板的要求,且其具有良好的耐水性;用于黏接有机玻璃、钢化玻璃、聚四氟乙烯、橡胶、玛瑙等基材也表现出较强的黏接力。

An efficient corrosion inhibitor of cassava starch graft copolymer for aluminum in phosphoric acid

Starch is one of the richest natural polymers with low-cost,non-toxic and biodegradable,but is seldom directly used as corrosion inhibitor due to its poor inhibitive ability and low water solubility.To solve this problem,cassava starch-acryl amide graft copolymer(CS-AAGC)was prepared through grafting acryl amide(AA)with cassava starch(CS),and it was firstly examined as an efficient inhibitor for 1060 aluminum in 1.0 mol·L^(-1)H_(3)PO_(4) media.The adsorption behavior of CS-AAGC and its electrochemical mechanism were investigated by weight loss and electrochemical methods.Additionally,the inhibited aluminum surface was fully characterized by a series of SEM,AFM,contact angle measurements and XPS.Results confirm that CS-AAGC performs better inhibitive ability than CS,AA or CS/AA mixture,and the maximum inhibition efficiency of 1.0 g·L^(-1)CS-AAGC is 90.6%at 20℃.CS-AAGC acts as a mixed-type inhibitor while mainly retards the anodic reaction.EIS has three time constants,and the polarization resistance is significantly increased in the presence of CS-AAGC.The micrograph of inhibited aluminum surface is of hydrophobic nature with low surface roughness and little corrosion degree.

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.

Effect of Post-Added Water Amount on Pre-Concentrated Bark Foaming Materials by Mechanical Stirring

In this study,pre-concentrated bark,furfuryl alcohol and other biomass raw materials were used to prepare foaming materials by high-speed mechanical stirring without using a foaming agent.We investigated the effect of the postadded water amount on the properties of foaming materials.In particular,we determined basic physical properties of these materials,including the limiting oxygen index(LOI),porosity,thermal conductivity,thermogravimetric analysis,pore size distribution,and microstructure.The results of scanning electron microscopy(SEM)indicated that the pore size distribution was uniform and the pore size increased with increasing water volume.Thermogravimetric analysis(TG/DTG)showed that when the temperature reached 410°C,the foam was easily decomposed,the final residual mass was only 2.8%,and water addition had little effect on it.Moreover,the amount of post-added water is 5–30 g,the density and compression strength of the foamed materials gradually decreased,while the degree of pulverization increased.LOI ranged from 26.1%to 30.79%,and porosity ranged from 81%to 83%.The change in water volume greatly affected the foam’s performance,the performance of foamed material deteriorated as the amount of added water increased,but the effect on thermal conductivity was not very obvious.The highest thermal conductivity was only 0.0179 W/(m·K),still providing excellent thermal insulation.

Development of Antioxidant Packaging Film Based on Chinese Bayberry Tannin Extract and Polyvinyl Alcohol

The current work explores the potential use of commercial Chinese bayberry tannin(BT)to develop antioxidant PVA-based films using solvent casting process for packaging applications.The effect of BT concentration on opa-city,water resistance and antioxidant capacity of resulting films was investigated.Properties like tensile strength,thermal behavior,and morphological aspects were also characterized.The experimental results showed that PVA/BT films formed with uniformly brown color and generally good transparency,offering good antioxidant ability.The PVA film containing BT presented slightly higher water resistance according to the results of moisture content and water vapor permeability,especially at low BT content(<10 wt%).The PVA can be compounded with up to 10 wt%BT without any obvious deterioration in the tensile strength.The PVA/BT films exhibited better thermal degradation behavior compared with PVA alone because of the chemical bonds of PVA-BT and the for-mation of char at high temperature.Based on the results,PVA incorporated with Chinese bayberry tannin may provide broader formulation options for packaging materials with antioxidant action.

Assisted Compatibility, and Balanced Regulation of the Mechanical, Thermal, and Antioxidant Activity of Polyvinyl Alcohol-Chinese Bayberry Tannin Extract Films Using Different Di-Aldehydes as Cross-Linkers

Polyvinyl alcohol(PVA)-based films containing Chinese bayberry tannin(BT)were prepared by cross-linking using glyoxal,glutaraldehyde and dialdehyde starch,individually.The presence of cross-linkers was evident to promote the transparency and decrease the moisture content of PVA/BT films,while the water solubility stayed almost unchanged in the cross-linked PVA/BTfilms.All cross-linkers provided promotion of the water vapor per-meability,mechanical property and thermal stability of PVA/BT films.The best water vapor barrier capacity was found in case of glutaraldehyde cross-linked PVA/BT film,while the highest tensile strength was encountered in case of glyoxal cross-linked PVA/BT films,compared with the uncross-linked films.The scavenging action of the films towards DPPH radical activity was influenced by the nature of each cross-linker.Namely,the PVA/AT film cross-linked by glutaraldehyde acquired the lowest radical scavenging activity in a certain time,suggesting that glutaraldehyde decreased the release rate of BT from PVA.Based on the experimental data,glutaraldehyde and dialdehyde starch could be more suitable for PVA/BT film preparation since they can promote the intermo-lecular interaction of PVA and BT to a reasonable extent.

Lightweight Biobased Polyurethane Nanocomposite Foams Reinforced with Pineapple Leaf Nanofibers (PLNFs)

Pineapple leaf nanofibers(PLNFs)extracted from pineapple leaf fiber were used for reinforcing biobased polyurethane foam(BPU).The dispersion performance of PLNF in the foaming mixture system,nanocomposite foaming behavior,cell morphology,cell size,density,compressive strength and dimensional stability were investigated.The viscosity of the mixtures increased with increasing the PLNF content.The addition of a tiny amount of PLNF did not influence the exothermic temperature of the foam system,but reduced the expansion and gel time of the nanocomposite foams.This reduced time was found to increase the production efficiency.Scanning electron microscopy(SEM)images showed that the PLNF neither affected the cell shape nor size.While the density of the foam was not obviously altered with the addition of a small amount of PLNF,the compressive strength and dimensional stability were significantly improved.

Preparation and Characterization of Sandwich Structured Materials with Interesting Insulation and Fire Resistance

A cellular material in the form of 3-layered sandwich structure material was prepared via sole use of mechanical stirring without any use of a foaming agent,while Tween-80 was employed as a foam stabilizer via a developed in-situ mold casting.The resulting structure displayed a good appearance with no visual defects.The 3-layered composition of the sandwish structure,“nonporous resin layer-porous foam layer-nonporous resin layer”,was examined in terms of the microstructure,density&density distribution,pulverization ratio,mechanical strength,insulation and flame retardant performance.It was indicated from the results that the bonding between the resin layer and foam layer was tight,while the tensile rupture always occurred in the porous layer.Also,the density of the sandwich structure material was symmetrical with“saddle”distribution,and a uniform density for any given layer.The increase in the density at the interface layer provided a good interpretation for the tensile rupture never occurred at the interface.The brittleness resistance of the developed material was significantly improved,and the pulverization ratio was sharply decreased from 9.93%to 0.31%.The material acquired a thermal conductivity and limiting oxygen index(LOI)of 0.0241 W/m⋅K and 29.92%,respectively,indicating potential use of such materials broadly in fields of insulation and flame retardancy.

Preparation of an Abrasive Grinding Wheel Based on Tannin Resin Cross- Linked by Furfuryl Alcohol, Urea and Glyoxal

Simple bio-based abrasive grinding wheel based on thermosetting resin matrix was developed starting with condensed tannin and furfuryl alcohol,which are mainly derived from forest and agricultural products like tree barks,wheat and crops.Fourier transform infrared spectra(FTIR)signified the acidic conditions are quiet efficient for the reaction of furfuryl alcohol,urea and glyoxal all together and the-CH_(2)-NH-and-CH_(2)-O-CH(OH)-groups are predominating in cross-linking of the tannin-furfuryl alcohol-urea-glyoxal(TFUG)resin.The strengthening contribution of the tannin was also confirmed by the preservation of its distinct crystallinity using X-ray diffraction(XRD).Differential scanning calorimetry(DSC)and thermogravimetric analysis(TGA)ensured that TFUG resin can be cured at low temperature and offer higher heat resistance compared with phenol-formaldehyde(PF)resin.The high hardness and excellent compressive strength revealed by the corresponding investigations such as Brinell hardness,compression resistance,and grinding tests suggested a strong abrasive ability using the new grinding wheel compared with lab-made grinding wheel based on PF resin.This could be ascribed to the absence of cracks and low content of formed holes as confirmed using scanning electron microscopy(SEM)and balanced reaction conditions that leads to network structure with regular local reinforcements and homogeneous crosslink density.

Preparation of cobalt ferrite nanoparticles using fulvic acid as a capping agent and its effect on catalytic activity

Cobalt ferrite was prepared by co-precipitation from cobalt and iron soluble precursors in presence of fulvic acid at different pHvalues, namely, 6 and 8 and compared with the same preparation in absence of fulvic acid. The presence of fulvic acid is expected tobind metal ions through bridging before co-precipitation and mineralization. The extent of binding is determined according to thepH of the process. This influences the mineralization of the resulting cobalt ferrite and the crystallization/ordering of its lattice. Inaddition, the extent of residual ferric oxide is also a function of the efficiency of binding process. This route of modification for the coprecipitationprocess was found to be accompanied by enhanced surface area and total pore volume for most of the prepared samples.The involvement of these oxides as catalysts in the photo-catalytic degradation of phenol from wastewater was found to contributevery efficiently and the removal reached about 88% in some cases, which can be attributed to olation and oxolation process of theformed nanoparticles.

Competitive polycondensation of model compound melamine-urea-formaldehyed(MUF)resin system by^(13)C NMR

Melamine-urea-formaldehyde(MUF)resin is an excellent adhesive in the field of wood adhe-sives,however the competition mechanism is questionable which affects the structure control and performance optimization of the resin.In this study,the competitive resin synthesis poly-condensation reaction of MUF system under alkaline condition was studied based on the model compound 1,3-dihydroxymethyl urea(UF_(2))and melamine(M)system,and the competitive reac-tion mechanism in the system was deduced by^(13)C NMR quantitative analysis.The results show that the energy barrier of hydroxymethylation of melamine is lower than that of urea,and the priority of hydroxymethylation is lower;the addition of melamine results in a large amount of hy-drolysis of UF_(2),and the formed free formaldehyde,resulting in hydroxymethylation of melamine;there is obvious polycondensation reaction in UF_(2)+M system,mainly from the relationship be-tween hydroxymethylurea and melamine or hydroxymethylmelamine.The type I bridge bond structure of polycondensation mainly comes from the reaction of UF_(2) and M,which is difficult to form the type II bridge bond.At low molar ratio,the formation of bridge bond is superior to that of ether bond.With the increase of molar ratio,the formation of ether bond shows advantages,but there is obvious competition between them.There may be competitive presence of the UF self-condensation products,melamine-formaldehyde(MF)self-condensation products and MUF co-condensed products after the polycondensation reaction.