Polyurethane material has good physical and mechanical properties, excellent weatherability, flexibility and hardness with little change in temperature and other advantages. It has been widely used in many fields. With the improvement of environmental protection laws and regulations and the strengthening of peopleâ€™s awareness of environmental protection, the water-based polyurethane materials have received increasing attention. The research and development of waterborne polyurethanes have important application values. In order to better improve the comprehensive performance of waterborne polyurethanes and expand the application range, the research on modified waterborne polyurethanes has become a hot topic in recent years. Many researchers have conducted in-depth research and the modification methods are also changing rapidly. At present, the modification methods can be roughly divided into four types: (1) improving monomer and synthesis process; (2) adding additives; (3) performing cross-linking; (4) optimizing compounding. Among them, the optimization of compounding is most noticeable. According to different modifiers, the modification of waterborne polyurethane emulsions mainly includes: modification of epoxy resin, modification of polysiloxane, modification of acrylic acid, and composite modification of nanomaterials.
1 Epoxy resin modified waterborne polyurethane 1.1 Characteristics of epoxy resin Epoxy resin (EP) has many excellent properties, such as easy to cure, high mechanical strength, strong adhesion, low molding shrinkage, good chemical stability, and electricity. With good insulation, low cost, high modulus, high strength and good thermal stability, it has long been widely used in thermosetting plastics and plays an increasingly important role in the fields of machinery, electronics, and coatings. However, epoxy resins also have some outstanding drawbacks, such as poor toughness, low impact strength, and brittleness after curing, which limits their application in certain fields. Epoxy resins have secondary hydroxyl groups and epoxy groups and can react with isocyanates. The epoxy resin modified waterborne polyurethane will have improved mechanical properties, bonding strength, water resistance, solvent resistance and other properties.
1.2 Preparation of Epoxy Modified Waterborne Polyurethanes There are two main methods for preparing epoxy modified waterborne polyurethanes: mechanical blending and copolymerization. The blending method generally involves synthesizing a polyurethane prepolymer first, then dispersing an appropriate amount of the epoxy resin in the prepolymer, and then emulsifying the prepolymer mixed with the epoxy resin to obtain the epoxy resin-modified water-based resin. Polyurethane emulsion. In the epoxy resin modified waterborne polyurethane emulsion obtained by the mechanical blending method, there is no chemical bond between the epoxy resin and the polyurethane, and the epoxy resin is not hydrophilic, and the carboxyl group and the polyether chain segment in the polyurethane chain have water resistance. Affinity, when the two are emulsified in water, the epoxy resin is coated in the polyurethane chain, and it is possible to 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, followed by the hydroxyl groups on the epoxy resin molecules to participate in the reaction to make a prepolymer, and then emulsify in water. In addition, a ring-opening reaction occurs between the urethane group and the epoxy group, and this method is a cross-linking reaction.
There are three main types of epoxy resin feeding methods: First, the epoxy resin and polyether polyol are added to the reactor at the initial stage of the reaction; second, the epoxy resin and the small chain extender are added together during the middle period of the reaction. The reactor; thirdly, the epoxy resin and the hydrophilic chain extender are added together into the reactor at the later stage of the reaction.
1.3 Application and Research Progress of Epoxy Modified Waterborne Polyurethane Epoxy modified waterborne polyurethane has been applied in adhesives and coatings. Guo Junjie and others synthesized epoxy resin-modified waterborne polyurethane adhesives for bonding composite films. The modified adhesives exhibited strong adhesive properties to a variety of composite films. The peel strength was further improved, and the appearance and storage stability were improved. Good, and still has strong adhesive properties after the solid mass fraction has dropped to 30%. Anhui University used epoxy resin and polyurethane grafting reaction to synthesize epoxy modified polyurethane emulsion. The resulting emulsion prepared floor varnish with small odor, good film luster and certain elasticity. It was dried after 1 day and used well. .
Jiang Shouxia et al studied the effect of the content of epoxy resin in waterborne polyurethane emulsions on performance. It was found that after adding epoxy resin, the water resistance of the product was significantly improved. With the increase of the epoxy resin content, the hardness also increased, and the viscosity was increased. Upward trend. Luo Jianguang found that the copolymerization method is harder to obtain a stable emulsion than the mechanical blending method. The reason may be that the copolymerization method generates partial branching structure due to EP in the prepolymerization stage, which increases the viscosity of the prepolymer and affects the emulsification; in addition, the epoxy group in the emulsion obtained by the copolymerization method is catalyzed by triethylamine. Under the ring, cross-linked substances form and precipitate.
2 Silicone Modified Waterborne Polyurethanes 2.1 Characteristics of Organic Silicones Silicone polymers contain elemental silicon in their molecular structure, which is a semi-organic, semi-inorganic polymer compound. They have the characteristics of both organic and inorganic compounds and have low temperature resistance. , weather resistance, electrical insulation, ozone resistance, hydrophobic, flame retardant, physiological inertia and many other excellent properties.
The most prominent characteristics of silicone polymers are oxidation resistance and low surface energy, oxidation resistance is good weatherability, and low surface energy produces excellent hydrophobicity. Silicone products generally refer to polysiloxane series, including modified polysiloxanes such as non-reactive polysiloxanes, reactive polysiloxanes, epoxy groups, hydroxyl groups, and amino groups. Silicone-modified water-borne polyurethane can make up for the poor water-resistance of water-borne polyurethane, making the modified waterborne polyurethane exhibit good hydrophobicity, surface enrichment, low-temperature flexibility and excellent biocompatibility.
2.2 Silicone modification methods Silicone modified waterborne polyurethanes are also two methods of blend modification and copolymerization modification. Blending can be achieved by physical blending of an aqueous polyurethane emulsion and a silicone emulsion. Polyurethanes can improve the oil resistance of polysiloxane emulsions, while polysiloxane emulsions can improve the water and solvent resistance of waterborne polyurethanes, and the effects of blending the two can be lengthened. However, due to the presence of emulsifiers, the blending modification has a negative impact on the final film forming performance. The blending modification is merely a simple mechanical mixing, no chemical bond formation, the silicone oil is easy to migrate, and the silicon sensing has a short aging time. Copolymerization modification is the most commonly used method for silicone-modified waterborne polyurethanes. It is a polysiloxane oligomer with reactive functional groups at both ends (eg hydroxy silicone oil, amino silicone oil, amino or alkoxy-terminated silane coupling agent). Etc.) and polyisocyanates are gradually added and polymerized to obtain block copolymers.
Silicone copolymerized modified waterborne polyurethane preparation methods mainly include two different methods of synthesis and chain extension. The synthesis method introduces hydroxy silicone oil or amino silicone oil into the polyurethane segment during the synthesis of the prepolymer. The reactivity of hydroxy silicone oil is moderate, the synthesis process is stable, and it is better controlled than amino silicone oil. The chain extension method refers to the introduction of amino silicone oil chain extension during the emulsification of the prepolymer.
2.3 Application and Development of Silicone Modified Waterborne Polyurethane Silicone modified waterborne polyurethane can be widely used in coatings, leather industry, printing industry, textile industry and other fields.
Wu Mingyuan et al. used aminopropylpolysiloxane to react with polyurethane prepolymers to produce siloxane-containing polyurethane prepolymers. The NCO groups were blocked by NaH-SO3 and dispersed in water to obtain silicone-modified heat-reactive waterborne polyurethanes. Emulsion. Hou Menghua et al. obtained a waterborne polyurethane emulsion modified with an aminosilane coupling agent in a solvent-free manner by using a chain extension method. The wood coating obtained by the waterborne polyurethane emulsion modified by the silane coupling agent has excellent water resistance. Sex, adhesion and mechanical properties. Liu Hongzhi et al. added TDI to a mixture of polyether diols and hydroxyl-terminated silicone monomers for reaction. The resulting prepolymers were 1,4-butanediol for chain extension reaction, followed by DMPA hydrophilic chain extension. And, emulsification, synthesis of silicone modified polyurethane emulsion, research shows that the silicone modified waterborne polyurethane material has improved water resistance, heat resistance and low temperature resistance.
3 Acrylic Modified Waterborne Polyurethane 3.1 Characteristics of Acrylate Compound Acrylate (PA) has excellent light resistance, outdoor exposure durability, that is, resistant to ultraviolet light is not easy to decompose yellow, can maintain the original color and luster, there are Good resistance to acid and alkali salts, excellent flexibility and lowest pigment reactivity. Acrylic modified waterborne polyurethane (PUA) can combine polyurethane with high tensile strength and impact strength, excellent abrasion resistance and good adhesion and weather resistance of acrylate resin, can produce high solid content, low cost And to achieve the use of water-based resin requirements.
3.2 Methods of Acrylate-Modified Waterborne Polyurethane There are many methods for synthesizing acrylate-modified waterborne polyurethane. Here, only the preparation method of the copolymer emulsion will be briefly described.
The preparation methods of the copolymerization emulsion mainly include the following: (1) Blending of PU emulsion and PA emulsion, plus a cross-linking agent to form a polyurethane-acrylate blended composite emulsion; (2) first synthesizing a PU polymer emulsion; The seed emulsion was then subjected to acrylate emulsion polymerization to form a PUA composite emulsion having a core-shell structure. (3) The two emulsions penetrated each other with molecular linearity, and then reacted to form a PUA composite emulsion of a polymer interpenetrating network. These methods subtly improve the compatibility of PU and PA. (4) Synthesis of an unsaturated urethane monomer with a C=C double bond, followed by emulsion copolymerization of the macromonomer with other acrylate monomers to give a PUA copolymer emulsion.
The chemical principle of preparing PU dispersion and PA emulsion is different. The former is addition polymerization, and the latter is radical polymerization. Therefore, the key to preparing PUA dispersion is to combine these two different chemical principles using a suitable process. It forms latex particles with a core-shell multiphase structure. Studies have shown that in order to prepare a high-performance PUA dispersion with a core-shell multiphase structure, a unique process must be used to combine the above two polymerization mechanisms and use special materials. In the past 10 years, researchers have continuously developed new raw materials and new processes that are suitable for the preparation of PUA dispersions.
3.3 Acrylic modified waterborne polyurethane research progress Acrylic modified waterborne polyurethane is widely used in leather finishing, coatings, adhesives, fabric coatings, printing and dyeing and other industrial fields. Xie Weibin synthesized an acrylic modified waterborne polyurethane and applied it to the cotton fabric coating. The test coated cotton fabric showed that the introduction of methyl acrylate can improve the water resistance of the coating film, increase the tensile strength of the coating film, and facilitate the introduction of hydroxyethyl acrylate. Coating film permeability, increase coating film elongation. Ai Zhaoquan developed a polyurethane-modified acrylate-based water-based series of decorative decorative adhesives with multiple functional groups that can be used as high-frequency adhesives, heat-sealing adhesives, and cold-adhesives. Chen Wen et al. synthesized waterborne epoxy acrylate resin and waterborne urethane acrylate, and then formulated it into a water-based UV-curable wood floor coating with excellent properties. The waterborne UV-curable material has the advantages of non-toxicity, no pollution, no stimulation, and production safety. , There are broad application prospects in the field of wood floor coatings. Zhou Jianjun successfully prepared a self-crosslinking PUA composite emulsion and obtained a core-shell structure (PA is a core, PU is a shell) of undispersed rubber latex. The stability of the emulsion is good, and its adhesive use test shows that the adhesive force, Water resistance is better. Tang Xun et al. synthesized a UV-curable aqueous anionic urethane acrylate. Synthetic water-based cured film has good adhesion, high hardness (>6H), high gloss (>90%), high tensile strength (>29MPa), and coating film has excellent water resistance, acid and alkali resistant Solvent and solvent resistance, can replace solvent-based wood floor light curing coating.
4Silicone Acrylate Double-Modified Aqueous Polyurethane <br> The ternary combination of polyurethane, acrylate, and organosilicone to prepare an aqueous material that combines the advantages of three resin materials: acrylate, polyurethane, and silicone, and Water as a dispersion medium meets the requirements of environmental protection. Combining the three organically combined, according to the requirements of different uses, and exerting the advantages of synergy, it can be made into a soap or soap-free emulsion, used as a textile coating agent and leather finishing agent.
There are mainly two methods for synthesizing silicone-acrylate double-modified water-based polyurethane. One is to first synthesize an appropriate amount of hydroxyethyl acrylate or hydroxypropyl acrylate-terminated polyurethane prepolymer, and then add an initiator to the emulsified aqueous PU. A mixture of acrylic monomers and silicone coupling agents, ie, a silicone acrylate double modified waterborne polyurethane. The other method is to first synthesize a silicon-containing polyurethane prepolymer and then add the acrylic monomer to be blended and then emulsify in water to obtain a silicon-modified polyurethane aqueous dispersion containing a swelling acrylate monomer, and then to the above-mentioned containing-swelling C.
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