Study on in situ preparation of nano calcium carbonate/PMMA composite particles
Introduction
The materials formed by embedding of inorganic particles into polymeric matrices represent a new class of polymeric materials that combine the properties of the inorganic particles (in terms of mechanical strength, modulus, and thermal stability) with the processability and the flexibility of organic polymer matrix. Of course, such materials can be obtained by simply mixing the organic and inorganic components. However, in order to achieve the best dispersion of the inorganic particle in polymer matrix and interfacial adhesion between the polymer and inorganic particle, the techniques for synthesizing composite particles made of inorganic particles coated by polymers have been developed [1], [2], including mini-emulsion [3], [4], suspension [5], dispersion [6], and emulsion polymerization [7], [8]. The soapless emulsion polymerization with organic monomers in the aqueous suspensions of inorganic particles has been considered as a promising and preponderant approach to prepare nano composite particles, because the organic components on the surface of inorganic particles can be synthesized in accordance with the applying systems. The inorganic particles can be well dispersed into polymer matrix. Moreover, due to lack of surfactants, the application fields of composite particles are enlarged compared with the products from emulsion polymerization. The prepared composite particles have great potential applications in Painting, Plastics, and Rubber, etc.
The inorganic particles were mainly nano silicon dioxide, nano titanium dioxide, nano aluminum oxide, etc., all of which have high surface activities and more active radicals [9], [10], [11]. Nano calcium carbonate that has lower surface activity and fewer active radical was used to prepare inorganic–organic nano composite particles by the technology only after its surface had been commendably modified by surfactants [12], [13], [14], [15], [16].
In the paper, it was innovatively validated that nano calcium carbonate without surface modification can also be well coated by polymers to form composite particles. The effects of synthesis parameters on monomer conversion were studied. The formation mechanisms of composite particles were proposed. The applications in epoxy varnish were investigated preliminarily.
Section snippets
Main raw material and reagents
Nano calcium carbonate in the form of filter cake was provided by Nanotech Science and Technology Ltd and produced by high gravity technology with a mean size of 40 nm, cubic shape and crystalline structure of calcite. Chemicals are generally reagent grade from commercial sources without further purification. Analytical-grade methyl methacrylate made by Beijing Yili Fine Chemicals Ltd was used as monomer. Analytical-grade ammonia persulphate (APS) made by Beijing Chemical Plant was used as
The effects of synthesis parameters on the preparation of nano composite particles
The basic technology of preparation of composite particles is soapless emulsion polymerization of methyl methacrylate in nano calcium carbonate aqueous suspension. The conversion is defined as the percentage of the mass of created polymer comparing with the total mass of monomer; its calculating formula is thatwhere C denotes the monomer conversion; M1 denotes the dried mass of composite particles; M2 denotes the mass of added calcium carbonate; M3 denotes the mass of added
Discussions of formation mechanism of nano composite particles
Based on the previous investigation, a formation mechanism of composite particles is proposed:S2O82−→SO4−•
At the beginning, there are few radicals in the system. The probabilities of termination reactions among increasing radicals chains is low. The collision probabilities of increasing radicals chains with nano calcium carbonate particles are high. Although CaCO3 is a electrovalent bonded compound, the CO32− is covalence radicals which contain CO double bonds. The increasing polymer chains
Conclusions
In this paper, the effects of synthesis parameters on monomer conversions were studied. The formation mechanism of composite particles was proposed. The conclusions obtained in the paper are as follows:
- (1)
Appropriate amounts of nano calcium carbonate can promote soapless emulsion polymerization of methyl methacrylate. Increasing stirring rate can enhance the probabilities for polymer to coat on the surface of nano calcium carbonate. When the temperature is lower than 80 °C and the dosages of
Acknowledgments
Prof. J.F. Chen would like to thank the support by the National Natural Science Foundation of China (no. 20236020, 20325621), the National R&D Program of China (no. 2001BA310A01), the Talent Training Program of the Beijing City (no. 9558103500), and the Fok Ying Tung Foundation (no. 81063).
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