Progress In Research And Application Of Waterborne Polyurethane Modification

Bao Junjie 1, Zhou Haifeng 1, Rao Ximei 1, Xu Gewen 1, 2

(1.. College of chemistry and chemical engineering, Anhui University, Hefei 230039; 2. Key Laboratory of green polymer in Anhui Province, Hefei 230039)

Abstract: several common modification methods of waterborne polyurethane such as nano modification, vegetable oil modification, montmorillonite modification and organic fluorine modification were reviewed, and the characteristics, methods and advantages of different modification technologies were pointed out.

The applications of waterborne polyurethane in wood coatings, automotive coatings, architectural coatings, anticorrosive coatings and fabric coatings were also introduced.

Key words: waterborne polyurethane resin; modification; coatings; progress

Waterborne polyurethane resin has the advantages of high hardness, strong adhesion, corrosion resistance, good solvent resistance and low VOC content. It meets the "three premise" and "four E principle" of coating industry.

However, the general polyurethane emulsion has poor self consistency, low solid content, poor water resistance, low gloss, and poor comprehensive properties of the film. In order to better improve the comprehensive performance of waterborne polyurethane coatings and expand the application scope, WPU emulsion needs to be modified properly.

At present, its modification approaches can be roughly divided into four categories: improved monomer and synthesis process, adding auxiliaries, carrying out crosslinking and optimizing composite.

This paper mainly introduces the research and application of waterborne polyurethane coatings, such as epoxy resin modification, polysiloxane modification and acrylic acid composite modification, nano modification, vegetable oil modification, montmorillonite modification, organic fluorine modification, and application in wood coatings, automotive coatings, building coatings, anticorrosive coatings and fabric coatings.

1 waterborne polyurethane modification technology

1.1 traditional three major modifications

At present, the three most common modification methods of waterborne polyurethane coatings are epoxy resin modification, silicone modification and acrylic acid modification.

In recent years, a large number of such methods have been reported.

Epoxy resin is polyhydroxy compound. In the reaction with polyurethane, branching point can be introduced into polyurethane backbone, forming a partial network structure with better performance.

Epoxy modified polyurethane emulsion was prepared by graft copolymerization of epoxy resin and polyurethane, and waterborne epoxy modified polyurethane coating was prepared with this method. The chemical stability, corrosion resistance and adhesion of paint film could be improved.

Organosilicon compounds contain elemental silicon. They are semi organic and semi inorganic polymer compounds. They possess the characteristics of organic compounds and inorganic compounds.

Silicone modified polyurethane can make up for the poor hydrolysis resistance of waterborne polyurethane, so that modified waterborne polyurethane coatings exhibit good hydrophobicity, surface enrichment, low temperature compliance and excellent biocompatibility.

Silicone modified polyurethane can be carried out by physical blending. For example, waterborne polyurethane and polysiloxane emulsion are used for physical blending modification.

Therefore, the most commonly used method of silicone modified polyurethane is copolymerization modification.

Block copolymers were prepared by polymerization of polysiloxane oligomers with reactive functional groups at the ends (most commonly of poly two methylsiloxane PDMS, or partially substituted methyl siloxane) and polyisocyanates.

Acrylate has many outstanding advantages compared with other synthetic polymer resins.

Acrylic polyurethane hybrid water dispersions prepared from two kinds of polymers of acrylic acid and polyurethane under microcosmic state can obtain complementary advantages.

Waterborne polyurethane / acrylate composite emulsion can combine polyurethane with higher tensile strength and impact strength, excellent abrasion resistance and good adhesion, weatherability and lower cost of acrylic resin.

In addition, the polyurethane acrylate polysiloxane three yuan can be combined to prepare waterborne coatings, which combines the advantages of acrylic resin, polyurethane and silicone three kinds of resin materials, and the water dispersing medium meets the requirements of environmental protection.

1.2 nano materials modified waterborne polyurethane

Nanomaterials have special properties such as surface effect, small size effect, optical effect, quantum size effect and macroscopic quantum size effect.

Carbon nanotubes / waterborne polyurethane nanocomposites were synthesized by Hsu-Chiang Kuan and [1]. The waterborne polyurethane emulsion was stable, the thermal stability of the film increased by 26, the tensile strength increased by 370%, and the tensile modulus increased by 170.6%.

Hu Jinxin et al. [2] uses waterborne polyurethane as the matrix polymer material, and uses polymer nano microencapsulation technology to effectively encapsulate inorganic TiO 2 particles. The mechanical strength, toughness and aging resistance of the coating are improved, and the processing performance is improved.

Luo Zhenyang and other [3] added nano alumina (Al 2 O 3) and nano indium tin oxide (ITO) to waterborne polyurethane resin respectively, which improved the wear resistance and heat insulation performance of waterborne polyurethane film.

Feng Libang and other [4] have successfully synthesized a waterborne polyurethane coating containing nano silicon oxide. The results show that the introduction of nano silicon oxide can significantly improve many physical properties of polyurethane film, such as surface hardness, thermal stability, weatherability and water and solvent resistance.

Zhao Shilin and other [5] used waterborne polyurethane resin and nano SiO 2 to prepare waterborne nano UV shielding pparent coatings by blending method.

The environment-friendly nano UV shielding pparent coating, as the cover of building exterior wall coatings and wood coatings, can improve the UV shielding rate of the coatings and maintain high pparency, thus prolonging the service life of the coatings.

Shi Yongjian et al. [6] used acrylic modified waterborne polyurethane to synthesize waterborne PUA with excellent comprehensive properties, which was used as film forming material. Nano Al 2 O 3 was used as filler to prepare coatings. The nano Al 2 O 3 composite coating with excellent wear resistance was prepared when nano Al 2 O 3 was added at 4%.

Nanocomposite coatings with good thermal insulation properties were prepared by using nano indium tin oxide (ITO) as filler.

Using synthetic waterborne polyurethane as the film-forming material and nano SiO 2 as filler, the nano composite coating prepared by nano SiO 2 has an average shielding rate of 59.35% and a pmittance of over 90% in the visible light when the amount of nano SiO 2 is added.

Professor Chen Su of Nanjing University of Technology and other molecular assembly technology used inorganic nano particles and polyurethane polymers to assemble organically, thus obtaining nano waterborne polyurethane wood coatings with superior comprehensive properties.

The emulsion has good stability, ageing resistance, chemical resistance, abrasion resistance and antistatic property.

1.3 vegetable oil modified waterborne polyurethane

Vegetable oil is a renewable resource. The preparation of waterborne polyurethane coating with vegetable oil can further reflect environmental awareness. Zhou Yingping and other [7] crosslinked waterborne polyurethane coatings, which are synthesized from vegetable oils, have not only good weatherability, but also pollution-free waterborne coatings. They are environmentally friendly coatings, which can be used as waterborne interior and exterior wall coatings as well as wood-based decorative coatings and textile printing and dyeing coatings.

Qiu Wei and other [8] used air drying vegetable oil as the basic raw material, modified it and implanted it into the semi sealed PU molecular chain. The self emulsifying single component water PU was prepared. The emulsion had good stability and excellent mechanical properties.

Cui Jinfeng and other [9] used linseed oil and two ethanolamine to react to form linoleic two ethanolamine intermediates. The waterborne PU coatings synthesized by this intermediate are water-resistant, fast drying, strong adhesion, non-toxic, non flammable, sticky and easy to control. They are excellent environmental friendly waterborne coatings.

Flaxseed oil, castor oil and decarboxylated cashew nut shell liquid (CNSL) are renewable and non-toxic natural vegetable oils.

Wang Hongyu et al. [10] used linseed oil instead of solvent or water as dispersing medium. It was prepared by reaction of castor oil and toluene diisocyanate and introducing OH decarboxylate cashew nut shell liquid to prepare polyurethane / linseed oil composite coating.

Cui Jinfeng and other [11] use dry vegetable oil (linseed oil, tung oil) and glycerol (glycerol) alcoholysis to form glycerol ester intermediates, and prepare intermediate temperature crosslinking waterborne polyurethane resin with this intermediate. The waterborne resin can be used to prepare one component polyurethane waterborne ink for gravure printing.

The research shows that the ambient temperature crosslinking water polyurethane resin synthesized by this alcoholysis method can meet the intaglio printing ink manufacturing process suitability, gravure printing operation suitability and product quality applicability. The water-based ink has high light and water resistance, strong adhesion and dry adjustable, bright colors, clear layers, non-toxic, non flammable, weather resistant, sticky and easy to control. Compared with other water-based gravure ink, it has wide adaptability to all kinds of substrate materials, and is an excellent environment-friendly water-based intaglio printing ink.

1.4 Montmorillonite Modified Waterborne Polyurethane

Montmorillonite is an inorganic layered silicate whose crystal structure consists of two layers of silicon oxide tetrahedra sandwiched with aluminum oxide eight faces.

Montmorillonite lamellae and matrix have two kinds of combinations on nanometer scale: first, the nano effect of montmorillonite lamellae dispersed in the matrix at nanometer scale, making the interface between montmorillonite lamella and the interface stronger; two, the montmorillonite lamella is not completely separated, but the intercalation of molecular chains is completed. After intercalation polymerization, the movement of molecular chains is restricted by the lamellar layer of montmorillonite, which makes the relatively free molecular chains fixed in the interlayer of montmorillonite, and plays a role of crosslinking point in the matrix.

The montmorillonite modified waterborne polyurethane composite material perfectly combines the rigidity, dimensional stability and thermal stability of inorganic silicate chip with polymer toughness and workability. It has special structure and excellent performance, and can be widely applied in various fields.

Montmorillonite modified solvent polyurethane has been reported more, and water based reports have been taught less.

Hou Menghua et al. [12] used montmorillonite, TDI, DMPA gamma propyl triethoxy silane as raw materials. The waterborne polyurethane emulsion was prepared by intercalation polymerization. Silane coupling agent and montmorillonite modified waterborne polyurethane had the effect of complementary performance. When adding 1% montmorillonite and 2% coupling agent, the tensile strength and elongation at break of Waterborne Polyurethane film increased by 69.7% and 17.6% respectively, and the water absorption rate decreased by 48.7%.

1.5 organic fluorine modification

Chen Jianbing et al. [13] used mercapto ethanol as a chain pfer agent and synthesized by free radical polymerization.