Mechanically Assisted Surface Modification of Polymer Particles with Superfine Calcium Phosphates
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Ltd.,
5-7,
2-chome,
Jonanjima,
Ohta-ku,
ABSTRACT A mechanical route plays an important role in particulate coatings and synthesis. A type of particulate surface modification, i.e., oriented coating of fine particles onto the surface of a core particle, is proposed. For achieving this concept, the author has developed a two-step process involving mechanical and chemical methods. As an example, needle-like dicalcium phosphate fine particles were coated, in a standing-up state, onto the surface of nylon-12 core particles (avg 50um). The effect of the crystal structure of dicalcium phosphate on the particulate oriented coating was investigated. INTRODUCTION Particulate materials, designed from morphological and/or compositional points of view, can be prepared by a mechanical method, e.g., surface modification of polymer particles with zirconia via mechanical dry embedding method [1] or synthesis of magnesium titanate through mechanochemical reaction [2]. The author has recently studied the surface modification of nylon-12 particles with calcium phosphate nanoparticles, where both fabrication and coating of the nanoparticles were accomplished by mechanical means [3,4]. Purpose of the present study is to further develop the application of mechanical way to "advanced particulate design". Particulate properties can be strongly affected by particulate surface structure. Conventional surface modification of particles through particulate coating can be classified into (1) monolayer coating, (2) film forming (microencapsulation), and (3) multi-layer coating [1]. These types of surface modification can be accomplished by a dry process using mechanical impact energy. This paper proposes a new type of surface modification, i.e., oriented coating of fine particles onto the surface of a core particle. It is impossible to be achieved only via a mechanical process. For achieving this concept, a mechanical and chemical two-step process is designed, as shown in Fig. 1. Firstly, inorganic fine particles are mechanically embedded onto the surface of a polymer particle. Then, the fine particles, serving as crystal nuclei, grow into a special shape, e.g., needle-like, under certain conditions. An experiment on surface modification of nylon-12 (avg 501am) via the above two-step process has been conducted in order to obtain some basic knowledge about this concept.
327 Mat. Res. Soc. Symp. Proc. Vol. 501 ©1998 Materials Research Society
Fine Particles (Inorganic) 0
Ordered Mixture Mixing
Core Particle
(Polymer)
*e Crystal Growth in a Solution Chemical Process Composite Particle with Oriented Coating
composite particle
Figure 1. The mechanical and chemical two-step process for oriented coating of fine particles onto the surface of a core particle. EXPERIMENTAL The mechanical operation was carried out by using the Hybridization System (NHS-0, Nara Machinery Co. Ltd.) which consists of several parts including the Hybridizer, the main part of the system, as shown in Fig. 2. The mechanical process is as follow. Firstly, a mixture con
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