Technical progress of the most popular modified wa

Progress in modified waterborne polyurethane technology

polyurethane materials have many advantages, such as good physical and mechanical properties, excellent weather resistance, little change in elasticity and soft hardness with temperature. It has been widely used in many fields. With the improvement of environmental protection laws and regulations and the strengthening of people's awareness of environmental protection, the hydration of polyurethane materials has been paid more and more attention. The research and development of waterborne polyurethane has important application value. In addition, because the material of this part is metal, so as to better improve the comprehensive properties of waterborne polyurethane and expand the scope of application, the research on modified waterborne polyurethane has become a hot spot in recent years. Many researchers have conducted in-depth research, and the modification methods are changing with each passing day. At present, the modification methods can be roughly divided into four types: (1) improve the monomer and synthesis process; (2) Additive; (3) Implement crosslinking; (4) Optimize composition. Among them, optimized composition is the most attractive. According to different modifiers, the modification of waterborne polyurethane lotion mainly includes: epoxy resin modification, polysiloxane modification, acrylic acid modification, nano material composite modification, etc

1. Epoxy resin modified waterborne polyurethane

1.1 characteristics of epoxy resin

epoxy resin (EP) has many excellent properties, such as easy curing, high mechanical strength, strong adhesion, low molding shrinkage, good chemical stability, good electrical insulation, low cost, high modulus, high strength and good thermal stability. It has already become a widely used thermosetting plastic in machinery, electronics Coatings and other fields are playing an increasingly important role. However, epoxy resin also has some outstanding shortcomings, such as poor toughness, low impact strength, brittle after curing, which limits its application in some fields. Epoxy resin has secondary hydroxyl group and epoxy group, which can react with isocyanate. The mechanical properties, adhesive strength, water resistance and solvent resistance of waterborne polyurethane modified by epoxy resin will be improved

1.2 preparation methods of epoxy modified waterborne polyurethane there are two main preparation methods of epoxy modified waterborne polyurethane: mechanical blending method and copolymerization method. Generally, the blending method is to synthesize polyurethane prepolymer first, then evenly disperse an appropriate amount of epoxy resin in the prepolymer, then emulsify the prepolymer mixed with epoxy resin, and finally obtain the waterborne polyurethane lotion modified by epoxy resin. In the epoxy resin modified waterborne polyurethane lotion prepared by mechanical blending method, there is no chemical bond between epoxy resin and polyurethane, and the epoxy resin is not hydrophilic, while the carboxyl group and polyether segment in the polyurethane chain have affinity for water. When both are emulsified in water, the epoxy resin is coated in the polyurethane chain, which may form a certain core-shell structure. The copolymerization method mainly uses the epoxy groups at both ends of the epoxy resin chain to preferentially copolymerize with the polyurethane prepolymer, and then the hydroxyl groups on the epoxy resin molecules participate in the reaction to prepare the prepolymer, which is then emulsified in water. In addition, there is a ring opening reaction between carbamate group and epoxy group, which is a cross-linking reaction

there are three main feeding processes for epoxy resin: first, epoxy resin and polyether polyol are added to the reactor at the initial stage of the reaction; Secondly, the epoxy resin and the chain extender were added to the reactor together in the middle of the reaction; Thirdly, epoxy resin and hydrophilic chain extender were added to the reactor at the later stage of the reaction

1.3 application and research progress of epoxy modified waterborne polyurethane

the application of epoxy modified waterborne polyurethane in adhesives and coatings has been reported. Guojunjie and others have synthesized epoxy resin modified waterborne polyurethane adhesive for bonding composite films. The modified adhesive shows strong bonding performance to a variety of composite films, with further improved peel strength, good appearance and storage stability, and still has strong bonding performance after the solid mass fraction is reduced to 30%. Anhui University has synthesized epoxy modified polyurethane lotion through the grafting reaction between epoxy resin and polyurethane. The floor varnish prepared with the obtained lotion has small odor, good gloss and certain elasticity. It is dry after 1 day and has good application effect

jiangshouxia et al. Studied the influence of the content of epoxy resin in waterborne polyurethane lotion on the performance, and found that after adding epoxy resin, the water resistance of the product was significantly improved. With the increase of the content of epoxy resin, the hardness also increased, and the viscosity showed an upward trend

luojianguang et al. Found that it is more difficult to obtain stable lotion by copolymerization than by mechanical blending. The reason may be that the viscosity of the prepolymer increases due to the formation of partial branched chain structure in the prepolymerization stage of EP, which affects the emulsification; In addition, the epoxy group in the lotion prepared by copolymerization method opened the ring under the catalysis of triethylamine, formed a cross-linking compound and precipitated

2. Organosilicon modified waterborne polyurethane

2.1 characteristics of organosilicon

organosilicon polymer contains element silicon in its molecular structure. It is a high molecular compound with semi organic and semi inorganic structure. It has the characteristics of both organic and inorganic compounds, and has many excellent properties such as low temperature resistance, weather aging resistance, electrical insulation, ozone resistance, hydrophobicity, flame resistance, physiological inertia, etc. The most remarkable characteristics of organosilicon polymers are oxidation resistance and low surface energy. Oxidation resistance is good weather resistance, and low surface energy will produce excellent hydrophobicity. Silicone products usually refer to polysiloxane series, including non active polysiloxane, active polysiloxane, epoxy, hydroxyl, amino and other modified polysiloxanes. Silicone modified waterborne polyurethane can make up for the poor hydrolysis resistance of waterborne polyurethane, "said Mr. zhangweihua, head of the business section of the headquarters of golden medical business, in an interview, which makes the modified waterborne polyurethane show good hydrophobicity, surface enrichment, low softness and excellent biocompatibility

2.2 silicone modification methods

silicone modified waterborne polyurethane is also modified by blending and copolymerization. Blending can be realized by physical blending of waterborne polyurethane lotion and polysiloxane lotion. Polyurethane can improve the oil resistance of polysiloxane lotion, while polysiloxane lotion can improve the water resistance and solvent resistance of waterborne polyurethane. Blending the two can obtain the effect of learning from each other. However, due to the existence of emulsifiers, blending modification has a negative impact on the performance of the final film. Blending modification is only a simple mechanical mixing, without chemical bond formation, and the silicone oil is easy to migrate, resulting in short silicon sensing aging. Copolymerization modification is the most commonly used method for modifying waterborne polyurethane with organosilicon. Block copolymers are prepared by step addition and polymerization of polysiloxane oligomers with reactive functional groups at both ends (such as hydroxyl silicone oil, amino silicone oil, amino or alkoxy terminated silane coupling agents, etc.) and polyisocyanates

there are two different methods for the preparation of waterborne polyurethane modified by organosilicon copolymerization: synthesis and chain extension. The synthesis method is to introduce hydroxyl silicone oil or amino silicone oil into the polyurethane chain segment during the synthesis of prepolymer. The reaction activity of hydroxy silicone oil is moderate, and the synthesis process is stable, which is better controlled than amino silicone oil. Chain extension method refers to introducing amino silicone oil for chain extension in the process of prepolymer emulsification

2.3 application and research progress of organosilicon modified waterborne polyurethane

organosilicon modified waterborne polyurethane can be widely used in coating industry, leather industry, printing industry, textile industry and other fields

wumingyuan et al. Reacted with aminopropyl polysiloxane and polyurethane prepolymer to form polyurethane prepolymer containing siloxane, blocked NCO group through nah-so3 and dispersed in water to prepare silicone modified thermal reactive waterborne polyurethane lotion. Houmenghua et al. Prepared the amino silane coupling agent modified waterborne polyurethane lotion by means of chain extension under solvent-free conditions. The wood coatings prepared by the silane coupling agent modified waterborne polyurethane lotion have excellent water resistance, adhesion and mechanical properties. Liuhongzhi et al. Added TDI to the mixture of polyether diols and hydroxyl terminated silicone monomers for reaction. The resulting prepolymer was subjected to chain extension reaction with 1,4-butanediol, and then the silicone modified polyurethane lotion was synthesized through DMPA hydrophilic chain extension, neutralization and emulsification. The research shows that the water resistance, heat resistance and low temperature resistance of organic silicon modified waterborne polyurethane materials have been improved

3. Characteristics of Acrylate Modified Waterborne Polyurethane

3.1 acrylate compounds

acrylate (PA) has excellent light resistance and outdoor exposure durability, that is, it is resistant to ultraviolet radiation, is not easy to decompose and turn yellow, can maintain the original color and luster for a long time, has good acid and alkali corrosion resistance, excellent flexibility and minimum pigment reactivity

acrylate modified waterborne polyurethane (PUA) can organically combine the high tensile strength, impact strength and excellent wear resistance of polyurethane with the good adhesion and weather resistance of acrylate resin, and can prepare waterborne resin with high solid content, low cost and meeting the use requirements

3.2 methods of Acrylate Modified Waterborne Polyurethane

there are many introductions on the synthesis methods of acrylate modified waterborne polyurethane. Here, only the preparation methods of copolymer lotion are briefly described

the preparation methods of copolymerized lotion are as follows: (1) Pu lotion and PA lotion are blended, and crosslinking agent is added to form polyurethane acrylate blend composite lotion; (2) First, Pu polymer lotion was synthesized as seed lotion, and then acrylate lotion was polymerized to form PUA composite lotion with core-shell structure; (3) The two lotion penetrate each other with molecular linear degree, and then react to form a polymer interpenetrating PUA composite lotion. These methods skillfully improve the compatibility of PU and PA. (4) The unsaturated carbamate monomer with C = C double bond was synthesized, and then the macromonomer was lotion copolymerized with other acrylate monomers to obtain PUA copolymerized lotion

the chemical principles for preparing PU dispersion and PA lotion are different. The former is addition polymerization and the latter is free radical polymerization. Therefore, the key to preparing PUA dispersion is to combine the two different chemical principles by adopting appropriate process to form latex particles with core-shell composite structure. The results show that in order to prepare high-performance PUA dispersion with core-shell multiphase structure, not only a unique process should be used to organically combine the above two polymerization mechanisms, but also some special materials should be used. Over the past 10 years, researchers have continuously developed new raw materials and new processes suitable for the preparation of PUA dispersions

3.3 research progress of Acrylate Modified Waterborne Polyurethane

acrylic modified waterborne polyurethane is widely used in leather finishing, coatings, adhesives, fabric coatings, printing and dyeing and other industrial fields. Xieweibin synthesized an acrylic modified waterborne polyurethane and applied it to the coating of cotton fabric. The test of coated cotton fabric shows that the introduction of methyl acrylate can improve the water resistance of the coating film, increase the tensile strength of the coating film, and the introduction of hydroxyethyl acrylate is beneficial to the permeability of the coating film and improve the elongation of the coating film. Aizhaoquan et al. Developed a series of water-based decorative adhesives containing multiple functional groups with polyurethane modified acrylate as the main body, which can be used as high-frequency adhesive, hot adhesive and cold adhesive. Chenwen et al. Synthesized waterborne epoxy acrylate resin and waterborne polyurethane acrylate, and then prepared Waterborne UV curable wood floor coating with excellent performance. The Waterborne UV curable material has the advantages of non toxicity, no pollution, no stimulation and production safety, and has broad application prospects in the field of wood floor coating. Zhoujianjun and others successfully made