Preparation And Properties Of Biological Cationic Waterborne Polyurethane Adhesive

At present,the domestic wood industry adhesive is still based on“Phenolic resin,urea-formaldehyde resin,melamine formaldehyde resin”adhesives which are prepared from non-renewable petrochemical industrial raw materials,the finished product can release free volatile organic compounds.The adhesive in the waste products is also difficult to degradation,which can cause adverse effects to the environment and human health.Therefore,it is particularly imporctant to seek alternatives to petroleum,reduce dependence on petrochemical resources,and develop high-performance bio-based adhesives to reduce and eliminate environmental pollution.As a new type of economic and environmental protection material,bio-based wood adhesive has attracted more and more attention in recent years.However,the production of bio-based wood adhesives also faces additional challenges.Adhesives made from renewable natural materials often have low water resistance or are too expensive to compete effectively with petrochemical derived polymers.Compared with anionic waterborne polyurethane,cationic products are less reported,and there are technical bottlenecks in product development.There are positive charges in the molecular chain of cationic waterborne polyurethane which has excellent adhesion to leather,glass and other anionic substrates,and good wetting property to hydrophobic substrates such as polyester and acrylic-based fabric fibers.Compared with similar anionic products,cationic products can provide better bonding strength.In this paper,polycaprolactone diol was used as the soft section of polyurethane to prepare high-performance cationic waterborne polyurethane,which was modified by bio-based polyols with hydrophobicity and degradability.In order to prepare cationic waterborne polyurethane adhesive which can meet various adhesion properties and is environmentally friendly and biodegradable.five kinds of isocyanate such as Hexamethylene diisocyanate(HDI),Toluene Diisocyanate(TDI),Diphenylmethane Diisocyanate(MDI),dicyclohexylmethane diisocyanate(HMDI)and Isoflurone diisocyanate(IPDI),respectively and polycaprolactone polyols(PCL-OH),hydrophilic group methyl diethanolamine(MDEA)and chain extender 1,4butanediol(BDO)system were used to prepare bio-based cationic waterborne polyurethane resin(WPU).Then castor oil(CO),epoxy soybean oil(ESO)and trimethylol propane monoleate(TMPM)were used to modify the properties of PCL-WPU emulsion,respectively.The effects of modifying agent dosage and hydrophilic MDEA content on film properties were discussed.The structure of the polymer was characterized by FT-IR and ~1H-NMR,and the appearance,viscosity,stability and film forming performance of the emulsion were studied.The mechanical properties and water resistance of the film were analyzed and tested.At the same time,the adhesive strength of various modified emulsions on plywood and splastic-wood floor were also investigated.The results are as follows:(1)Stable cationic waterborne polyurethane emulsion with high solid content was prepared via low hydrophilic group.Among the five kinds of WPUs prepared by different isocyanates,The preparation process of IPDI-WPU was relatively simple,the reaction was mild and easy to operate,and the film performance was relatively excellent.;To improve the mechanical performance,water resistence and adhesive strength of the waterborne polyurethane films,different amounts of castor oil(CO)acting as a cross-linking agent were incorporated in the polyurethane structure.The stable aqueous dispersion was obtained even when N-MDEA loading was as low as 3.23 wt%;a bonus of this low hydrophilic moiety was the excellent adhesive strength,whose T-peel strength could reach up to 36.8 N/25 mm,about114%higher than that of WPU(17.2 N/25 mm)without any CO content.When CO content was 9.66wt%,the elongation at break of WPU film reached 391%,water absorption decreased from 23.2%to 13.9%.(2)WPUs modified with epoxy soybean oil(ESO)was prepared.When the content of ESO was 7.99wt%and 10.37wt%,The film showed the characteristics of strong and tough.and the addition of ESO achieved the characteristics of toughening.The heat resistance of the film was analyzed by TGA and DTG.The first three samples all showed a stage of intense thermal decomposition,and the peak temperatures of rapid decomposition were 341.5℃,349.7℃and358.1℃,respectively,while ESO-WPU-4 and ESO-WPU-5 showed two stages of intense thermal decomposition.The peak temperatures of rapid decomposition in the second stage were 392.8℃and 403.5℃,respectively.With the increase of ESO content,the water resistance of the film was also greatly improved:when ESO content increased from 0 to 7.99wt%,water absorption decreased from 23.0wt%to 11.1wt%.(3)PCL-WPU emulsion was modified by biodegradable trimethylolpropane monoleate(TMPM)with long fatty side chain.The T-peel strength of TMPM-WPU-3 was 42.8 N/25 mm,which was 324%higher than that of WPU without TMPM(10.1 N/25 mm).The elongation at break of TMM-WPU-5 was 811%.When the TMPM content increased from 0 to 7.84wt%,the surface tension of the emulsion decreased from 53.6 m N/m to 41.5 m N/m.Water contact angle increased from 52.4?to 81.0?,Water absorption decreased from 15.6wt%to 9.6wt%;The tensile strength of WPU films decreased and the toughness increased.The cationic WPU modified by TMPM showed excellent film forming properties,flexibility and water resistance.After 45 days of simulated composting,the TMPM-WPU-5 sample with TMPM content of7.84wt%showed the highest degree of film damage,which implied the introduction of TMPM effectively improved the degradability of polymer films.(4)Eucalyptus plywood was bonded with various adhesive prepared with the the main resin of CO-WPUs,ESO-WPUs and TMPM-WPUs,respectively.The peel strength of eucalyptus plywood by IPDI-WPU,TDI-WPU and MDI-WPU exceeded the standard(GB/T17657-2013),which was 0.76MPa,1.12MPa and 1.24MPa,respectively.In terms of adhesive modified CO:Compared with CO-WPU1 without castor oil,the bonding strength of CO-WPU2 increased by 47.6%,and the peel strength of CO-WPU4 reached the maximum of0.91MPa.In terms of adhesive modified with ESO:When the addition amount of ESO reached7.99wt%,the adhesion performance of ESO-WPU4 was the best,and the peel strength of ESO-WPU4 reached 1.18MPa.In terms of adhesive modified with TMPM:The peel strength of TMPM-WPU2 with TMPM content of 2.10wt%was increased by 35.4%,the bonding strength of TMPM-WPU3 reached the maximum of 0.82MPa.The plastic-wood composite and black walnut veneer were bonded with the prepared series adhesives and the surface peeling strength of each plastic-wood composite floor was tested.The bonding strength of TDI-WPU and MDI-WPU to plastic-wood composite floor was 1.10MPa and 1.15Mpa,respectively,which exceeds the requirements of standard T/CNFPIA 3004-2019.Among the series of ESO-WPUs adhesions,the bonding strength of ESO-WPU3,ESO-WPU4,ESO-WPU7 and ESO-WPU8 to plastic-wood composite and black walnut veneer was 1.10MPa,1.21 MPa,1.10MPa and 1.04MPa,respectively.