Preparation and Characterization of Polysulfide Sealant Microcapsules Based on in situ Polymerization of Urea and Formaldehyde†

doi:10.7503/cjcu20170417

Abstract

Abstract:

A novel microcapsule of polysulfide sealant was designed and prepared by in situ polymerization technology with poly(urea-formaldehyde) resin(PUF) as shell material and polysulfide rubber as core material under the weak acid conditions. The microencapsulating process of core material, the morphology and chemical structure of microcapsule were monitored and characterized by surface observation and Fourier-transform infrared spectroscopy(FTIR) techniques, respectively. At the earlier stage of emulsification and dispersion, it was found that the particle diameter of dispersed polysulfide rubber decreased nonlinearly with the increase of PVA-124 concentration and PVA-124 was the best emulsifying agent among the various stabilizers studied. Through a large number of experiments, the following optimized conditions for the emulsification and dispersion of polysulfide rubber were obtained: using 1.5%(mass fraction) PVA solution as dispersion phase and PhMe as diluter, stirring speed 500 r/min and stirring time 0.5 h. At the later stage of polymerization reaction, we found that when the pH of solutions was adjusted to 2.5—3.5 and the reaction temperature was kept at 25 ℃, the polysulfide rubber microspheres could be gradually coated by PUF with the increase of reaction time, and the polysulfide rubber microspheres were completely encapsuled after the polymerization reaction was continued for 6 h. Then the products were placed in dry oven at 50 ℃ for one day after filtering. The results indicated that PUF microcapsules containing polysulfide rubber could be successfully synthesized, which had regularly spherical shape, rough outer surface and good dispersion. In addition, the optical photos of microcapsules showed that the average particle diameter was about 200 μm. Based on the detailed examining of some affecting factors such as emulsifier types and its concentration, stirring speed, reaction temperature and pH value, the optimum prepared condition was obtained. The quantitative analysis results revealed that the encapsulation efficiency of the core materials was 73% and the content of polysulfide sealant in microcapsules was 65% by ultraviolet(UV) spectrophotometer. The present work provides a valuable help for the further investigation and industrial application for the pre-coated technology of polysulfide sealant in the future.

Key words: Polysulfide rubber, Urea-formaldehyde resin, In situ polymerization, Microcapsule

CLC Number:

TrendMD:

WANG Xuan, JIN Tao, WANG Haowei, LIAO Shengzhi, YANG Huaiyu. Preparation and Characterization of Polysulfide Sealant Microcapsules Based on in situ Polymerization of Urea and Formaldehyde^†[J]. Chem. J. Chinese Universities, 2018, 39(2): 397.

Figures/Tables 10

References 23

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Type of dispersion stabilizer (1%, mass fraction)	Effect of emulsifying and dispersion for polysulfide sealant
Tween 80	Not dispersed, and reunited after standing
Span 80	Spherical particles with clear boundary, but largely difference in particle size and adhesion between particles
TX-100	Not dispersed, agglomerated into a block after standing
SDBS	Uniformly dispersion, the particles were spindle type
Methylcellulose	Mostly spherical particles with clear boundary and partial particles were spindle type, small difference in particle size
Arabic gum + gelatin	Non-uniformly dispersion, irregular shape and largely difference in particle size, partially reunited after standing
PVA-124	Uniformly dispersion, well-defined spherical particles with clear boundary, little difference in particle size
PVA-1799	Uniformly dispersion, spherical particles with clear boundary, but largely difference in particle size
PVA-1750	Poor dispersion, irregular shape, largely difference in particle size

Type of dispersion stabilizer (1%, mass fraction)	Effect of emulsifying and dispersion for polysulfide sealant
Tween 80	Not dispersed, and reunited after standing
Span 80	Spherical particles with clear boundary, but largely difference in particle size and adhesion between particles
TX-100	Not dispersed, agglomerated into a block after standing
SDBS	Uniformly dispersion, the particles were spindle type
Methylcellulose	Mostly spherical particles with clear boundary and partial particles were spindle type, small difference in particle size
Arabic gum + gelatin	Non-uniformly dispersion, irregular shape and largely difference in particle size, partially reunited after standing
PVA-124	Uniformly dispersion, well-defined spherical particles with clear boundary, little difference in particle size
PVA-1799	Uniformly dispersion, spherical particles with clear boundary, but largely difference in particle size
PVA-1750	Poor dispersion, irregular shape, largely difference in particle size

Reaction temperature/℃	Encapsulation effect of polysulfide sealant
25	Completely encapsulated, well-defined spherical particles with thick wall, little wall materials precipitated
30	Completely encapsulated, well-defined spherical particles with thick wall, little wall materials precipitated
40	Partially encapsulated, poor spherical particles with thin wall, little wall materials precipitated
50	Encapsulated, particle shape was irregular and large materials precipitated
60	Completely encapsulated, spherical particles with thin wall, large wall materials precipitated
80	Partially encapsulated, spherical particles with thin wall, large wall materials precipitated

Reaction temperature/℃	Encapsulation effect of polysulfide sealant
25	Completely encapsulated, well-defined spherical particles with thick wall, little wall materials precipitated
30	Completely encapsulated, well-defined spherical particles with thick wall, little wall materials precipitated
40	Partially encapsulated, poor spherical particles with thin wall, little wall materials precipitated
50	Encapsulated, particle shape was irregular and large materials precipitated
60	Completely encapsulated, spherical particles with thin wall, large wall materials precipitated
80	Partially encapsulated, spherical particles with thin wall, large wall materials precipitated

pH	Encapsulation effect of polysulfide sealant
2	Completely encapsulated, well-defined spherical particles with thick wall, but large precipitation and low utilization for the wall materials
2.5	Completely encapsulated, well-defined spherical particles with thick wall, but large precipitation and low utilization for the wall materials, and large difference in size
3	Completely encapsulated, well-defined spherical particles with thick wall and uniform size, little precipitation and high utilization for the wall materials
3.5	Completely encapsulated, well-defined spherical particles with thick wall and uniform size, little precipitation and high utilization for the wall materials
4.5	Well encapsulated, well-defined spherical particles with thick wall, but large precipitation and low utilization for the wall materials