Zinc oxide whiskers

Zinc oxide whiskers possess the following attractive physical properties  

Highly regular morphology and size. General zinc oxide whiskers are needle-like or particles with different sizes, while polygonal zinc oxide whiskers have a uniform structure and size. 

Good isotropy. The composites made with zinc oxide whiskers have good isotropic mechanical, electrical, and optical properties because of the isotropic structure and properties of zinc oxide whiskers. 

Semiconductor performance. The n-type semiconductor (resistivity = 7.14 il-cm) is formed when polygonal needles of polygonal zinc oxide whiskers overlap with each other. The resin matrix composites reinforced by polygonal zinc oxide whiskers could be used to make electronic 

Color Shape Density (glcm ) Diameter (pm) Length (pm) Tensile Strength (GPa) Elasticity Modulus (GPa) Moh s Scale of Hardness Melting Point (°C) 

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Isotactic polypropylene composites with tetra-needle-shaped zinc oxide whisker were prepared via melt blending in a twin-screw extruder. The whisker is a p-nucleating agent, which offers higher crystallization temperature, smaller sphemlites, and faster crystalhzation rate than can be obtained in neat iPP. The addition of whisker also increases heat deflection temperature and thermal degradation temperature of iPP composite. ... 

Table 3.5 Physical and Chemical Properties of Zinc Oxide Whiskers... 

Ultraviolet absorption. Zinc oxide whiskers have obvious ultraviolet absorption properties, which could be used to improve the aging resistance of polymers. 

High density. Zinc oxide whiskers can be used to make composites with sound insulation, shock absorption, and vibration resistance properties because of their high relative density (5.78 g/cm ). 

Like other acicular whiskers, general acicular zinc oxide whiskers are mainly used as reinforcing agents in composites tetragonal acicular ZnO whiskers are also used to prepare functional composites because of their unique structure. They are employed to improve some properties of composites, such as tensile strength, flexure resistance, wear resistance at room temperature, as well as chemical and dimensional stability at high temperature. 

Chen et al. treated zinc oxide whiskers via in situ polymerization. The first step is the dispersion process of zinc oxide whiskers. First expose zinc oxide whiskers to air for 24 hours, after which a large number of zinc oxide groups are produced. Then dry for 2 hours at 120°C. Then submerge the whiskers into an ethanol solution of APTS (y-aminopropyltriethoxysilane) and stir for 10 hours at 80°C. The sample is treated in an ultrasonic tank and then dried. 

The second step is the polymerization process between the treated whiskers and matrix. First, a certain amount of zinc oxide whiskers, aniline, and ethanol are mixed and stirred in a magnetic stirrer. Then 0.01 mol/L hydrochloric acid is added dropwise while stirring to trigger the polymerization reaction, which is done in an ice bath at 0°C-2°C for 10 hours. Then the polymerized products are treated for 10 minutes in a centrifuge at 3000 rpm and dried for 24 hours in a vacuum furnace. 

Liu et al. 5 treated zinc oxide whiskers using several different coupling agents. Table 3.14 shows the contact angles using different coupling agents with a concentration of 4 wt%. 

Figure 3.17 Infrared spectrum of zinc oxide whiskers before and after modification.

Weiping Liu, Jianping Zhou, Keqiang Qiu. Surface modification and characterization of zinc oxide whiskers. China Plastics Industry, 32(5) 47-49, 2004. 

For example, Chen et al. prepared zinc oxide whisker/ polyaniline core-shell composite material using in situ polymerization. The specific operation is as follows. A certain amount of treated zinc oxide whiskers, aniline, and ethanol are well mixed then the appropriate amount of 0.01 mol/L HCl is added dropwise with stirring in an ice bath of 0-2°C to initiate polymerization and the mixture is reacted for 10 minutes. The reaction mixture is centrifuged, filtered, and then dried in a vacuum furnace at 50°C for 24 h. 

When polygonal needle-like zinc oxide whiskers are added to matrix resin, adjacent needles overlap with each other and form a conductive path, which makes the transmission of charge possible, gives electrical conductivity to material, and also gives the polymer material a certain antistatic property. 

It can therefore be used as a filler for antistatic plastic. Wu prepared a conductive membrane with good performance by using zinc oxide whisker as packing material and polyvinyl alcohol and poly(methyl methacrylate) as the matrix. 

He found that zinc oxide whiskers can effectively improve the conductive property of PP resin. When the whisker volume fraction reaches 3%, the resistivity of the material decreases to below 10 Q cm, which is seven orders of magnitude lower than the resistivity of a pure PP matrix, whose resistivity is 10 Q cm and could meet the requirement of a general antistatic material. Wan and Jin put zinc oxide whiskers into an epoxy resin and obtained the same findings. Zhou et al. believed that there are three kinds of conductive mechanisms in the system network conduction, tunnel effect, and point discharge effect. 

The heat conduction of whiskers relies mainly on lattice vibration, namely phonon vibration thus thermal conductive performance is excellent, whereas the heat conduction of polymer materials depends mainly on internal vibration between atoms, which makes the thermal conductive performance poor. If whiskers are filled into polymers, they overlap with each other in a matrix and form pathways of heat conduction. Therefore the thermal conductivity of the composite will be greatly increased. Zhou found that low filling content can effectively improve the thermal conductivity performance of epoxy resin. When the whisker content is only 10%, the thermal conductivity of the material increased by 3 times compared with the pure matrix. Li et al. found that the thermal conductivity of PP filled with 30% zinc oxide whiskers increased by 55.9% over pure PP. 

Shuhua He, Jianping Zhou, Wanli Fu. Study on electroconductivity of tetragonal zinc oxide whisker (T-ZnOW)/polypropylene composite. Fine and Specialty Chemicals, 15(ll) 29-32, 2007. 

Jing Shi. Study on tetra-needle-shaped zinc oxide whisker modifying nylon 6 and high density polyethylene. Chengdu Southwest Jiaotong University, 2008. 

Additives used in final products Fillers barium and strontium ferrites, boron carbide, calcinated clays, calcium carbonate, carbon black, carbon-silica dual phase filler, clays, dolomite, fumed silica, iron oxide, magnesium aluminum silicate, magnesium carbonate, mica, montmorillonite, nickel zinc ferrite, nylon fibers, pulverized polyurethane foam, quartz, silica carbide, soapstone, talc, zinc oxide Plasticizers naphthenic oil, polybutene, aromatic oil, esters of dicarboxylic acid Plasticizers adipates, aromatic mineral oil, paraffin oil, phosphates, phthalates, polyethylene glycol, processing oil, sebacates Antistatics dIhydrogen phosphate of 8-amlnocaprolc add. Iodine doping Antistatics carbon black, quaternary ammonium salt, zinc oxide whisker Antiblocking diatomaceous earth Release propylene wax Slip erucamide+stearamide ... 

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