Preparation And Study Of Melamine And Its Derivatives Modified Polyurethane

As the state began to limit VOC emissions, the waterborne polyurethane began to usher in a new development opportunities. Waterborne polyurethane has many advantages, such as, no pollution, excellent mechanical properties, safety, easy modification and good biocompatibility,etc. However, water resistance and poor heat resistance of the traditional waterborne、polyurethane is not is not satisfactory, mechanical strength should be improved, which partly limited application and promotion of the waterborne polyurethane, modified WPU materials is widely studied. Common methods of modified polyurethane are physical blending grafting, nanomaterials modification or crosslinking modification. Melamine is a trimer of cyanamide, with conjugated triazine ring, is stability at room temperature,with excellent heat resistance, will release a lot of nitrogen when the resin is made by its thermal decomposition, which can be used as a flame retardant. Melamine has a unique stable triazine ring structure and three allelic primary amino group, with considerable activity which can be reacted with isocyanates and directly introduced into the polyurethane chain. Isocyanate can reactive with hydroxymethyl which is the reaction product of melamine and formaldehyde, while high etherified melamine formaldehyde resin as a crosslinking agent widely used in water-based paint, which can cross-linking react with the anionic polyurethane, in order to achieve the purpose of modified cross-linking polyurethane, this paper modified polyurethane following three parts:(1) Preparation and characterization of modified melamine crosslinking waterborne polyurethane.Melamine as a crosslinking agent to modify WPU with two methods melamine modified polyurethane and urethane-modified rear diffuser, compared WPU with the same degree of cross-linked by TMP, the results show that ATR found melamine crosslinking modified WPU with expansion reaction is not complete; residual melamine did not participate in the reaction. Melamine directly crosslinked modified WPU films’tensile strength increased from 6.8 MPa to 13.45 MPa, broken elongation of flima decreased from 1069% to 643%. Three methods modified films’ tensile strength variation is that melamine cross-linked modified WPU> crosslinking modified WPU after chain extension> TMP crosslinked modified WPU, and broken elongation’s variation is on the contrary. The heat resistance of the modified WPU which is introducted of a triazine ring has been greatly improved, melamine modified WPU’s thermal decomposition temperature improved 69℃. TMP crosslinking the heat resistance is not improved much. Water resistance, acid and alkali resistance of Melamine crosslinking modified WPU film has been greatly improved. The overall performance of direct cross-linking melamine modified WPU is more excellent.(2) Preparation and characterization of trimethylol melamine crosslinking waterborne polyurethane modifiedMelamine and formaldehyde prepared by the reaction trimethylol melamine, after purification as an aqueous polyurethane crosslinking agent,1H NMR and C NMR analysis showed that the melamine resin prepared as trimethylol melamine, a series of modified waterborne polyurethane was preparated. Studie has shown that trimethylol melamine methylol groups reacted with isocyanates, melamine resin crosslinking improves the tensile strength of the modified WPU film hardness, tensile strength range to by 7 MPa tof 13.5 MPa, when the content of HMMM is 25%, increased 98.25%; broken elongation a is reduced from1050% to 400%, reduced 61.9%. With the increasing amount of melamine resin, the heat resistance of the film increases, the thermal decomposition temperature increased 60℃. The glass transition temperature of the soft segment is unchanged, the glass transition temperature of the hard segment is elevated. With increasing degree of crosslinking after film in water, acid and alkali liquid-absorbent first to reduce elevated, while the lowest degree of crosslinking was 20%, after the crosslinked film of water, acid and alkali resistance have been improved.(3) Preparation and Study of waterborne polyurethane modified by HMMMThe two methods of HMMM modified WPU is blending modified nonionic NPU and crosslinked modified anionic WPU, two kinds of modification methods are compared. ATR-FTIR showed that HMMM react with APU, the triazine ring is introduced into the polyurethane segment; FITR peak separation results show that increasing the hydrogen content of the modified APU with HMMM caused by interactions be weaken. With the content of HMMM increasing, average particle size of polyurethane emulsion becomes larger. With increasing HMMM content, modified NPU hydrogen bonding forces gradually increased, no change in particle size of emulsion. With the contentof HMMM increased, the heat resistance of the modified APU increased,when HMMM content of 10% the maximum rate of decomposition temperature increased 38℃, water resistance, acid and alkali resistance have been improved greatly. The heat resistance of modified NPU improved 18℃, lower than the crosslinking modification. Tensile strength and adhesion properties of anionic polyurethane is significantly improved when HMMM added, when the content of HMMM is 8%, the tensile strength increased by 124.6%, reached 14.5 MPa, broken elongation decreased by 62.59%, its peel strength increased 7.36 N/cm. The tensile strength of the modified NPU increased by 40%, the broken elongation dropped 43%, less than the degree of crosslinking modified films.