Influence Of Hard Segment Content And Type On The Performance Of Waterborne Polyurethane

With the worsening environment and shortage of oil resources, traditional solvent polyurethane industry is shrinking. Waterborne polyurethane (WPU) is more environmental-friendly, and gradually replaces the traditional solvent polyurethane. Waterborne polyurethane was synthesized by introducing hydrophilic groups in the polyurethane chains or used added emulsifiers which can make polyurethane soluble or disperse in water, formatting polyurethane dispersion.As well as the traditional polyurethane, waterborne polyurethane has the typical block structure. According to the difference of the segment polarity, the polyol is regarded as the soft segment of WPU, while diisocyanate and chain-extender are seemed as the hard segments. The interaction between the hard and soft segments dominates wear resistance, low temperature flexibility, hardness, heat water resistance and other properties of waterborne polyurethane. Therefore, the structure and content of the soft and hard segments have an important impact on the performance of waterborne polyurethane. This paper mainly discussed the influence of hard segment component, and mainly contained studying the effects of the content of the aliphatic diisocyanate in polyether-based WPU, chain-extender structure and the ion type of the hydrophilic chain extender on the particle size, infrared structure, thermostability, strain-stress and water resistance properties of waterborne polyurethane.(1) Effects of aliphatic diisocyanate content on the properties of polyether-based WPUA series of waterborne polyurethane with different diisocyanate content were synthesized by isophorone diisocyanate, polyether diol, dimethylol propionic acid, and diethylene glycol as main materials. Properties of waterborne polyurethane with different diisocyanate contents were studied through tests of the particle size, Fourier transform infrared spectra, differential scanning calorimetry (DSC), thermogravimetry (TG), tensile and water resistance.The result displayed that with the increase usage of diisocyanate, the mean particle size increased and the distribution became wider when the hydrophilic group was constant. There was no influence on the N-H stretching vibration when the usage of diisocyanate increased, and the free C=O stretching vibration absorption decreased while the hydrogen bonding C=O stretching absorption increased. Variable temperature infrared test indicated that as the temperature rising in 50-200℃, the hydrogen bonding interaction of WPU system gradually reduced, and N-H and C=O stretching vibration absorption peek obviously shifted to higher wave numbers. DSC test showed that the increasing isocyanate amount resulted in hydrogen bonding disintegrate platform at50℃of WPU gradually moving to higher temperature, and caused the material heat resistance properties down while the water resistance increase.(2) Influences of different chain-extenders on the performance of waterborne polyurethaneFirstly, polyurethane prepolymer which had low molecular weight, was synthesized using isocyanate and polymer polyols in the process of waterborne polyurethane. In order to improve the molecular weight, polyurethane prepolymer need chain extension. It is a better way to use small molecules diol chain-extender in consideration of the reaction activity differences.There are many common diols used for chain-extender, such as ethylene glycol, propylene glycol,1,4-butanediol, diethylene glycol, and so on.The chain-extender structure can change the waterborne polyurethane chain to some extent, which has an influence on the regularity of molecular chain, the thermostability, water resistant, and mechanical properties.In this chapter, series of WPU were synthesized using several types of chain-extender agents, such as straight-chain type chain extenders with different length of carbon chain, chain extenders with different numbers of side methyl group, and chain extenders with ether oxygen groups. Prepared WPUs were characterized through tests of particle size, infrared spectrum, thermostability, water resistance, and tensile property. This part emphasized the research regarding to relationships between N-H vibration absorption peaks change of WPUs and different structure of small molecules chain extension agents.The latex particle size test showed that prepared WPU using neopentyl glycol chain extender containing two side of methyl groups, presented minimum particle size and narrow distribution, while WPU based1,6-hexanediol presented largest particle size and widest distribution. IR spectra of N-H stretching vibration absorption curve fitting results informed that with the carbon atoms number of straight chain extender increase, the free N-H absorption peak content gradually increased, and the hydrogen bonding N-H absorption peak content between the hard segments gradually decreased, while the hydrogen bonding N-H absorption peak content rose gradually under the influence of hydrogen bonding between the soft and hard segments. The strength of the whole hydrogen bonding force had a downward trend with the growth of the carbon chain. The structure of the chain extender containing ether oxygen groups can enhance the hydrogen bonding interactions in the system. The heat resistance property of WPU went up as the carbon chain length of straight-chain type chain extender increased. Tensile and water resistance tests showed that the crystallization and hydrogen bonding force of WPU played a role in tensile strength and water resistance properties. Thus, the crystallization and strong hydrogen bonding force could improve materials tensile and water resistance properties.(3) Influences of Ion types on the performances of polycarbonate-based WPUThis part mainly studied effects of ion types of hydrophilic chain extender on the structure and properties of WPU. A series of WPU were synthesized using dimethylol propionic acid and N-methyl diethanolamine hydrophilic as chain extenders, and through adjusting the isocyanate and hydroxyl molar ratio. Ion types of the hydrophilic chain extender affected the molecular chain structure of WPU, thus had an impact on water resistance and mechanical properties. The structures of WPUs based two hydrophilic chain extender were compared by IR spectrum. Differential scanning calorimetry and thermal gravimetric analysis focused on the thermal performance of these two ion-type WPU. Tensile and water resistance properties of WPU films reflected materials macroscopic properties.The strength of the hydrogen bonding interactions of cationic waterborne polyurethane system was greater than the anionic system, through quantitative research of N-H stretching vibration absorption peak, and the qualitative analysis of C=O stretching vibration absorption peak of waterborne polyurethane based two type ions. Differential scanning calorimetry indicated the glass transition temperature of cationic waterborne polyurethane displayed upward trend with the increasing molar ratio of isocyanate and hydroxyl. TGA test results showed that the decomposition of the two ion types WPU had three main stages. Firstly, small molecules volatilized before200℃, followed by the decomposition the urethane, allophanate and polyester in the range of300℃-360℃, and then followed by the decomposition of the soft segment at420℃. Tensile and water resistance tests displayed that the cationic WPU were superior to the anionic WPU in terms of tensile strength, elongation at break and water resistance properties.