Fracture toughness of inorganic-organic hybrid coatings

2009

Telechelic glycidyl epoxide siloxanes substituted with either methyl, cyclopentyl, or cyclohexyl groups were cured thermally with corresponding telechelic aliphatic amine. Also, the three glycidyl epoxide functionalized siloxanes were homopolymerized via a photoinitiated cationic mechanism. Both the UV and thermal curing were performed by formulating with reactive diluents. The mechanical properties, viscoelastic behavior, and coatings properties of the thermally cured siloxanes were studied. In addition, the X-ray measurements were performed. The rate of polymerization increased with the increasing size of substituent on the siloxane backbone. The hardness, adhesion, and solvent resistance increased as the bulk of the substituent increased in the siloxane backbone. The release properties for adhesion and readhesion increased with increase in steric bulk of the backbone substituents. Crosslink density reduced and oxygen permeability increased with increase in siloxane substituent size. There was also an increase in the advancing and the receding contact angles with the increase in substituent size. The inverse dependency of substituent size and free volume was observed in the d-spacing of the X-ray data.

Section: Methodsmentioning

confidence: 99%

Mechanical and film properties of thermally curable polysiloxane

Chakraborty

2009

“…The plane‐stress fracture toughness ( K c , stress intensity factor at fracture) was calculated using eq. (1),26, 27 where w is the width, a is the notch length, b is the thickness, and F is the force at which crack propagation begins.…”

Section: Methodsmentioning

confidence: 99%

Microgel formation and thermo‐mechanical properties of UV‐curing unsaturated polyester acrylates

Nebioglu

2007

The effect of internal and terminal unsaturation on the properties of the acrylated polyester films was investigated. Four types of acrylated polyester resin were prepared using adipic acid, maleic anhydride, neopentyl glycol, trimethylolpropane, and acrylic acid. Terminal and internal double bond content as well as branching was adjusted by the molar quantities of trimethylolpropane and maleic anhydride, respectively. A reactive diluent, trimethylolpropane triacrylate (TMPTA), was also used. A three-factor, three-level Box-Behnken design was used to investigate complex nonlinear relationships. Dynamic mechanical, fracture toughness, and tensile properties were evaluated with respect to the amount of terminal and internal unsaturation, and reactive diluent concentration. It was found that microgel formation extensively affects the final UV-cured film properties. Small quantities of microgels function as micro-support units, whereas high extent of microgelation causes phase separation through cluster formation and hence, decreases the mechanical properties. It is essential to control the extent of microgelation and phase separation to optimize product performance.

“…K c (i.e., the stress intensity factor at fracture) was determined with the following equation:24 where w is the width, a is the notch length, b is the thickness, and F is the force at which crack propagation begins. The energy release rate per unit of crack area at fracture ( G c ) was calculated with the following equation:24 where E is the tensile modulus. The G c values were calculated with average values of K c and E .…”

Section: Methodsmentioning

confidence: 99%

Dual‐curable unsaturated polyester inorganic/organic hybrid films

Nebioglu

Teng

2005

An unsaturated polyester, based on maleic anhydride, 1,6-hexanediol, and trimethylol propane, was formulated with tetraethylorthosilicate (TEOS) oligomers and a coupling agent to prepare inorganic/organic hybrid films. TEOS oligomers were prepared through the hydrolysis and condensation of TEOS with water, and 3-(triethoxysilyl)propylisocyanate was used as the coupling agent between the organic and inorganic phases. The hybrid materials were cured by moisture via sol-gel chemistry and by the UV curing of unsaturated polyesters. To compare the properties of the moisture-cured inorganic/organic hybrid films, a conventional 2K polyurethane system was also prepared. The tensile, adhesion, abrasion, and fracture toughness properties were investigated as functions of the coupling agent and relative amount of UV cure versus thermal cure. Although no difference could be observed in the tensile properties, the abrasion resistance, fracture toughness, and adhesion were enhanced by the incorporation of TEOS oligomers into polyurethane films. Also, the abrasion resistance, fracture toughness, and tensile properties were increased with both moisture and UV exposure.