Preparation And Properties Of Dual-cure Solvent-free Cardanol-cased Coatings

Coatings are an important material supporting the national economy and is widely used in machinery,transportation,chemical,construction and other industries,but solvent-based coatings account for more than half of the market.In the process of preparation,construction,drying,curing and film formation of solvent-based coatings,a large amount of volatile organic compounds（VOC）are emitted into the atmosphere,which will cause pollution to the ecological environment.Therefore,it is of great strategic significance and broad application prospects to study environmentally friendly solvent-free coatings that meet the requirements of economy,ecology and energy.Cardanol is a by-product of cashew nut shell oil,and its molecular structure contains active phenolic hydroxyl groups,rigid benzene rings and unsaturated long aliphatic side chains.By modifying cardanol,cardanol-based coatings of different curing types can be prepared,such as cardanol-based heat-curing epoxy resin,cardanol-based air-curing resin,and cardanol-based light-curing resin.However,a single curing method has certain shortcomings,and it is a very meaningful work to achieve complementary advantages through dual curing.Based on the above considerations,this project used cardanol as the main raw material to prepare cardanol-based host resins and reactive diluents of different curing types.Compared with single curing,the influence of different curing methods on coating properties was systematically studied.The main content is divided into the following parts:（1）Preparation and properties of cardanol-based heat-air dual-curing coatings.Star-shaped cardanol-based resin（HF）was synthesized by ether exchange reaction of hydroxyethyl cardanol ether（HCE）and hypermethyl etherified melamine formaldehyde resin（HMMM）.The resin structure was characterized by Fourier transform infrared spectroscopy（FT-IR）and hydrogen nuclear magnetic resonance spectroscopy（¹H-NMR）,and the results showed that the resin was successfully prepared.The curing behavior of HF in air was investigated by FT-IR and differential scanning calorimetry（DSC）,and the effects of drier and curing temperature on the coating properties were systematically investigated.Oxygen resin is compounded for double cross-linking curing.The viscosity of the prepared coatings was tested by rheometer,and the mechanical properties,thermal stability and mechanical properties of the coatings were tested by universal material testing machine,thermogravimetric analyzer（TGA）,dynamic thermomechanical analyzer（DMA）,etc.The single-curing and double-crosslinking curing were compared,and the properties of coatings with different epoxy resin contents were studied,including the thermodynamic properties of cured films and the basic properties of coatings.The results show that:HF resin has a lower viscosity,and the double curing of HF and cardanol-based epoxy resin can increase the crosslinking density of the coating and improve the performance of the coating.With the increase of the addition amount of cardanol-based epoxy resin,the hardness,adhesion and T_g of the coating all showed an upward trend.When the content of epoxy resin was 40%,the comprehensive performance of the coating was the best,and the cured coating had the best overall performance.The pendulum hardness was 115 s,the pencil hardness was 3 H,the adhesion was grade 0,and the T_g was 80°C.（2）Preparation and properties of cardanol-based light-air dual-curing coatings.Photo-air dual-curable multi-arm cardanol-based oligomers were synthesized by the ether exchange reaction of HCE and hydroxyethyl acrylate（HEA）with HMMM.By controlling the ratio of HCE and HEA,different ratios of photo-air reactive functional groups were prepared of dual-cure oligomers（HCE_x-HEA_y）.The structure of the prepared resin was characterized by FT-IR and ¹H-NMR,the viscosity of the prepared coating was tested by rheometer,and the photocuring kinetics of HCE_x-HEA_y was explored by real-time infrared.The effects of the type and amount of photoinitiator on the curing properties of coatings were systematically studied,and their tensile properties,thermal stability and mechanical properties were tested by universal material testing machine,TGA,DMA,etc.The single-curing and double-crosslinking curing were compared,and the coating properties with different ratios of HCE and HEA were investigated,including the thermodynamic properties of the cured films and the basic properties of the coatings.The results show that the prepared dual-curing resins all have low fluid viscosity,and all formulations are suitable for preparing solvent-free coatings without adding any solvent to the system.The cured film has a certain mechanical strength through light curing,and air post-curing further improves the performance of the coating.With the increase of HCE dosage,the pendulum hardness,pencil hardness,adhesion and T_g of the dual-cured coating showed a trend of increasing first and then decreasing.When the sample was HCE₃-HEA₃,the coating had excellent comprehensive properties.The layer had a pendulum hardness of 150 s,a pencil hardness of 3 H,an adhesion level of 0,and a T_g of 90°C.（3）Preparation and properties of cardanol-based light-moisture dual-curing coatings.Two kinds of light-moisture dual-curing actives were synthesized by the hydrolytic condensation of two cardanol monomers containing different functional hydroxyl groups with 3-methacryloyloxypropyltrimethoxysilane（KH-570）,respectively.The structure of the diluent was characterized by FT-IR and ¹H-NMR,the viscosity of the resin was tested by a rheometer,and the photocuring kinetics of the reactive diluent was explored by real-time infrared.The dual-curing coatings were prepared by curing the two diluents with epoxidized soybean oil acrylate（AESO）.The mechanical properties,thermal stability and mechanical properties of the coatings were tested by universal material testing machine,TGA,DMA,etc.The effects of the addition of two reactive diluents on the coating properties,including the thermodynamic properties of the cured film and the basic properties of the coating,were studied.The results show that the two reactive diluents synthesized have lower fluid viscosity and higher double bond conversion.Compared with single photocuring,the T_g and storage modulus of the light-moisture dual-cured film were improved.With the addition of cardanol-based reactive diluent,the hardness,adhesion and T_g of the dual-cured coating showed an upward trend.When the content of reactive diluent PLR602-AA-KH570 was 30%,the coating had excellent comprehensive properties,the pendulum hardness of the cured coating is 76 s,the pencil hardness is 2 H,the adhesion is grade 2,and the Tg is 61°C.