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Influence of mechanical factors on surface layer of acrylic coatings modified with nanofillers
Over the last decade nanotechnology gained much interest, due to its large potential.The relevant benefits for coatings industry are its effect and properties evoked by the use of inorganic nanoparticles instead of conventional filler materials.
Water based nanocomposite dispersion, representing a innovative coating class for wood coatings and plastic are presented in this paper.These modern waterbased environmentaly frendly coating combine a soft film –forming polymerphase and a hard, non film forming polimer domain.This matrix of coating is a part “ from green technology “and can be formulated without solvents and show film hardness and good elasticity.
Among the nanofillers used in coatings formulation there are distinguised metal nanoparticles (such as: silver,copper) or metal compounds (iron oxides, zinc oxides, aluminium oxide, titanium dioxide, ziconium dioxide,SiO2 and calcium carbonate).
This water based nanonanocomposite dispersion can be obtain starting with acrylic nanopolymer (15-70 nm size), and 5-35% (mass) silica sol charged stabilised having primary particles with very fine sized (5-30 nm).
Fig. 1 - Primary nanosilica Fig. 2 – Coupling between silica surface and silane
Fig.3 Coupling mechanism between silica surface and silane
Fig. 4 Schematic presentation of bonded on silica surface (a) between silicas; (b) silica itself
Incorporation of nanofilers are made under pH control (9-10) and must to ensure that the inorganic particles are well distributed in the polimer net-work.
Fig.5. Scaning force microscopy of coating with PVC 23%, based on NC with 10% dry silica to dry binder; dark area:soft polymer, bright spots: hard silica
Only by homogenous fusion of organic and inorganic materials into the NC coating structure results in increased mechanical properties of dryed coatings and combine the cotradictory properties hardness and flexibility.
Experimental, the investigation of hardness of acrylic coatings was made following the standard test method DIN EN ISO 1522, using pendulum hardness tester and ISO 1518 using scratch tester.The results show that the silice modified acrylic coatings are more resistance with 20-60% than traditional acrylic coatings.
Fig 6 Hardness improvement
The resistance of coating to abrasion was tested using Taber abraser accordingly with ASTM D 4060.The lossing of weight after 50 cycles was decreased with 20-40% than the un modified acrylic coating.
One important feature for wood and plastic application is blocking resistance, which enables a fast stacking of fresly coated objects.The blocking resistance is impoved without modification on elasticity and Tg of polymer; The evaluation was made afrer ASTM d 2793;
The elasticity was evaluated complies with ISO 1520 using cupping tester and was observed that the elasticity of coat was not altere through addition of 5-35% silica sol.
1.Stefan Sepeur, Nanotechnology
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