疏水改性的聚对二甲苯薄膜对聚氨酯泡沫阻湿性能的影响

Effect of Hydrophobic Modification of Parylene C Film on Moisture Barrier of Polyurethane Foam

硬质聚氨酯泡沫(RPUF)的吸湿特性导致泡沫塑化、溶胀变形,影响其服役安全性及稳定性。但目前针对这种亲水性多孔界面的阻湿研究鲜有报道。通过表面改性的方法引入阻湿层是一种非常有效的解决方法,聚对二甲苯(Parylene C)可在室温沉积条件下形成致密薄膜,具有优异的阻湿性能。在RPUF表面沉积Parylene C薄膜,然后利用全氟小分子组装进行界面疏水改性。通过一维和二维红外、低场核磁、微观形貌和元素组成等表征以及不同厚度镀膜试样吸湿曲线等分析,阐明RPUF的吸湿机理及复合涂层体系阻湿的相关规律。结果表明:当Parylene C镀膜达到一定厚度后,RPUF表面的孔缺陷会被覆盖,其阻湿性能可提高73.6%,同时全氟小分子表面疏水改性后聚氨酯泡沫表面和水分子的相互作用和吸附会被减弱,进一步降低吸湿率。揭示了RPUF吸湿机理和Parylene C薄膜界面阻湿的基本规律,有望用于解决硬质聚氨酯泡沫的长效阻湿问题。

The rigid polyurethane foam(RPUF)with porous structure possesses the characteristics of low density,high strength,strong thermal insulation,excellent shock absorption property,and so on.Therefore,it is widely used in outer packing fields such as aviation,navigation,and precision instruments,and has many application prospects.However,there are random micron-scale pore structures and polar hygroscopic chemical groups on the surface of RPUF,which cause foam plasticization,swelling,and deformation due to moisture absorption.The existence of these unfavorable factors would influence the dimensional accuracy and mechanical properties of precision components,which seriously affect service safety and stability.However,there are few reports about moisture barrier research aimed at this hydrophilic porous polymer material.Fortunately,the introduction of a moisture barrier layer by surface modification is a very effective solution.Generally,the deposition temperature of the moisture barrier exceeds 50°C,which will cause outgassing and damaging to the polyurethane foam.Coating the RPUF surface is another strategy to make up for defects,as this kind of method is complicated and the organic solvents used in the coating make polyurethane foam swell and crack.In this paper,a fully shape-matched micron-scale moisture barrier film is growing on the surface of polyurethane foam using Parylene C room-temperature deposition technology.The advantages are that the conditions of the deposition process are mild and undamaged to the substrate,and the high crystallinity and high molecular weight of the coating can effectively conceal the pore defects on the surface of the RPUF.Besides,the film has good adhesion with RPUF,and possesses uniform thickness and compact structure,which can effectively block the penetration of water molecules.Meanwhile,perfluorinated small molecules with hydrophobic properties are assembled on the surface of Parylene C film by the method of vapor deposition.The interaction between the hydrophobic modified interface and water molecules are weakened,which further reduced the adsorption and penetration of water molecules for RPUF.In addition,the moisture absorption mechanism and moisture barrier laws of the composite coating system were elucidated through the characterization of one-dimensional and two-dimensional infrared,low-field nuclear magnetic resonance,microscopic morphology,and element composition,as well as investigation of the adsorption kinetic curves of samples with different thickness Parylene C film.Results show that there are abundant hydrophilic groups in the RPUF segment,such as–NH and–C=O,which create water molecules with high solubility in the RPUF and form hydrogen bonding interactions.On the other hand,the loosely arranged polymer segments also provide a larger free volume for the diffusion of water molecules.Meanwhile,the external water molecules can directly enter the RPUF,or adsorb on the inner wall of the pores to form a hydration layer that increases penetration and moisture absorption under the action of capillary forces,which is due to the existence of the pore defects on the RPUF surface.However,the surface energy is significantly reduced after the RPUF or Parylene C film surface undergoes hydrophobic modification by perfluorinated small molecules,which is beneficial to reduce moisture absorption and slow down the adsorption saturation time,although the moisture barrier effect is not obvious.Fortunately,the water contact angle of hydrophobic modification surfaces remains almost unchanged when undergoing long-term ultrasonic treatment,which shows excellent durability and is conducive to a long-term moisture barrier.Moreover,the number of pore defects and sizes on the RPUF surface are decreased with the increase of the thickness of the Parylene C coating.The results demonstrated that Parylene C film can completely cover the pore defects on the surface of RPUF when its thickness reached 40μm,and the property of the moisture barrier is improved by 73.6%.Meanwhile,the Parylene C film has excellent adhesion on the surface of RPUF,and high and low temperature and relative humidity impact tests have little effect on it.To summarize,the reason for the moisture absorption of the RPUF and the basic laws of the Parylene C film for moisture barrier are revealed,which is expected to be used to solve the issue of the long-term moisture barrier of rigid polyurethane foam.