Mechanical Properties and Structure of Melamine Formaldehyde/Poly(Vinyl Alcohol) Molecular Composites
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MECHANICAL PROPERTIES AND STRUCTURE OF MELAMINE FORMALDEHYDE/POLY(VINYL ALCOHOL) MOLECULAR COMPOSITES KECHENG GONG AND XINGHUA ZHANG
Dept. of Polymer Science & Tech., Guangzhou, P.R. China
South China Univ. of Tech.,
ABSTRACT The mechanical properties and structure of melamine formaldehyde (MF)/poly(vinyl alcohol) (PVA) composites were studied in this paper. When PVA content was less than a certain value(about 20 weight %), both flexible strength and impact resistance were improved obviously. While the impact resistance improvement remained the previous trend the flexible strength didn't increase so rapidly as before when the PVA content was more than 20%. The morphology and reactivity of the prepolymer powder and the morphology of the finished specimens were investigated by means of microscope, infrared spectrum and transmission electron microscope(TEM). The results indicated that molecular composite structure was formed in this two-component system. The well-distributed PVA in this system was beneficial to the formation of the molecular composite structure. That could explain the effects of PVA on the mechanical properties and showed that the molecular composite structure are favourable for making full use of the macromolecular potentiality. INTRODUCTION Since melamine was synthesized in 1834 by Liebig [1] its reactions with other chemicals have been studied. Melamine formaldehyde resin [21 extended the application of melamine. Like urea formaldehyde (UF) and phenolic formaldehyde (PF) resin, MF resin can be used as moulding and laminating materials, adhesive and coating.
In order to improve
its
toughness and to lower
its
cost, a lot of modified, reinforced or filled products are developed for practical uses 131. MF resin and its related products are often used in paper and textile industry 141. Particularly, the aqueous solution of MF and PVA is mainly used in papermaking r5).
The mechanical properties and structure of MF/PVA as mould-
ing material were studied in this paper. The results showed that the molecular composite structure benefited the improvement of the mechanical properties. EXPER IMENTAL Preparation of prepolymers When one mol 37% formaldehyde solution with pH 8.0-8.5 was heated to 60°C, 1/3 mol melamine was added into the solution. As melamine solved completely, the temperature was elevated to and kept at 85*C. As soon as one milliliter of this solution became turbid when it was mixed with three milliliters of water at room temperature, 5% aqueous solution of PVA was mixed with it. The liquid mixture was stirred at 850C for a period of time until it became a homogeneous mixture. After that, the liquid was put in a vacuum oven to eliminate water at 60°C for 72 hours. Mat. Res. Soc. Symp. Proc. Vol. 171. ©1990 Materials Research Society
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Then the solid obtained from the oven was grinded into prepolymer powder (90%). Ether bonds formed in processing. This was 1659 . proved by the increment 1200 900 1500 of 1050cm-lpeak(C-O-C . 1800 Wavenumbers (cm-i) asymmetric expansion vibration) in
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