Joining of carbon fiber reinforced polymer laminates by a novel partial cross‐linking process

Direct joining of partially cross‐linked and freshly infiltrated carbon fiber reinforced epoxy resin plates made from HTA/RTM6 is investigated as function of the partial curing degree. Partial cross‐linking maintains a certain chemical reactivity of the thermosetting resin which can be used for bonding to a second, freshly infiltrated resin part. A final curing cycle guarantees complete cross‐linking of the joined component. The bonding behavior and the interface morphology of the joined plates are analyzed by mechanical testing, acoustic emission analysis and microscopy. A significant dependence of the bonding and interfacial properties on the partial curing degree is found. Very low and very high partial curing degrees (below 70% and above 80%) result in low fracture toughness and discontinuous crack propagation. Intermediate curing degrees between 70% and 80% mainly show high fracture toughness, stable crack propagation and a ripple like interface morphology. The latter is created by the surface morphology of the partially cross‐linked plate with the typical peel‐ply imprint and results in a high contact surface and mechanical interlocking. The combination of chemical reactivity and high contact surface seems to be advantageous for the enhanced fracture toughness and the improved failure mode of samples with intermediate partial curing degree. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42159.     

UV‐activated silicone oligomer cross‐linking through photoacid and photobase organocatalysts

Diphenyl iodonium hexafluorophosphate salt and N‐alkyl morpholino acetophenone were shown to be effective photocatalyst generators for the cross‐linking of α,ω‐silanol terminated silicone oligomers. These two photoacid and photobase‐induced polycondensation pathways provided an attractive and efficient alternative to toxic and expensive organometallic catalysts. The utility of this novel UV‐curing process was demonstrated with a combination of time‐resolved infrared spectroscopy to follow the fast reaction kinetics and solid‐state ²⁹Si nuclear magnetic resonance to investigate the polysiloxane network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39875.     

Preparation of silica/polyurethane nanocomposites by UV‐induced polymerization from surfaces of silica

UV‐curable nanocomposites were prepared by the in situ photopolymerizaton with nanosilica obtained from sol–gel process. The photoinitiator 2‐hydroxy‐2‐methyl‐1‐phenylpropane‐1‐one (1173) was anchored onto the surface of the nanosilica with or without methacryloxypropyltrimethoxysilane (MAPS) modification. The photopolymerization kinetics was studied by real‐time Fourier transform IR (RTIR), and the microstructure and properties of the nanocomposite were investigated using transmission electron microscopy and UV–visible (UV–vis) transmistance spectra. RTIR analysis indicated that the nanocomposites without MAPS had higher curing rates and final conversion than those with MAPS. The nanocomposites with an uniformal dispersion of nanosilica had high UV–vis transmittance. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of vinyl‐polyhedral oligomeric silsesquioxanes‐reinforced silicone resin with three‐dimensional cross‐linking structure

A novel thermal stability and highly transparent silicone resin‐type material was prepared via hydrosilylation of vinyl‐polyhedral oligomeric silsesquioxanes (POSS)‐grafted methylhydrosilicone oil and vinylmethylsilicone oil in the presence of Karstedt catalyst. The morphology, mechanical property, thermal stability, optical transmittance, thermal‐oxidation resistance of the vinyl‐POSS‐reinforced silicone resins were systematically investigated. Scanning electron microscopy showed that the vinyl‐POSS‐reinforced silicone resins had good compatibility with polydimethylsiloxane (PDMS) systems. The mechanical analysis and thermo gravimetric analysis indicated that the mechanical properties and thermal stability increased with increasing quantity of vinyl‐POSS. However, the optical transmittance increased with the increasing amount of vinyl‐POSS rather than decreased. In addition, the incorporation of vinyl‐POSS did not improve the thermal resistance of the PDMS polymers. The product has the potential application for LED packaging. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42187.     

Light‐diffusing materials for LED illumination applications: Comparing the effectiveness of two typical light‐diffusing agents

Light‐diffusing materials (LDMs) are the primary lampshade materials used for indoor light‐emitting diode (LED) illumination. In this work, two varieties of typical LDMs filled with acrylic or silicone diffusing agents were fabricated via a twin‐screw extruder, and the influences of the particle size, refractive index and light‐diffusing surface area of the light‐diffusing agents on the properties of the LDMs, including their light‐diffusing properties, thermal stability and mechanical properties, were explored in depth. The results indicated that both acrylic and silicone light‐diffusing agents can be dispersed evenly in a polycarbonate (PC) matrix. The light‐diffusing surface area and refractive index are the main factors that influence the diffusing properties of LDMs. Compared with the silicone LDM, the acrylic LDM exhibited higher transmittance but poorer thermal stability and impact strength, making this material suitable for a rapid injection molding process to form half‐sphere covers that combine high haze and transmittance for LED light bulbs. Silicone LDMs exhibit good stability and impact strength, favoring a slow single‐screw extrusion molding process to prepare tubular or panel covers for tubular LED lamps and panel lamps. In this study, a method for producing LDMs with both high transmittance and high haze is reported. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42923.     

Effects of small molecular weight silicon‐containing acrylate on kinetics,morphologies, and properties of free‐radical/cationic hybrid UV‐cured coatings

A series of UV‐curable, silicon‐containing mixtures were prepared by adding different micro amounts of small molecular weight silicon‐containing acrylate KH570 to an interpenetrating polymer network system composed of cycloaliphatic polyurethane acrylate, trimethylolpropane triacrylate, cycloaliphatic epoxy resin, free‐radical photoinitiator Irgacure 754 and cationic photoinitiator Irgacure 250 with a weight ratio of 15 : 15 : 65 : 1 : 4. Hybrid coatings with different addition amounts of KH570 (0.2, 0.6, 1.0 wt %) were cured from the mixtures by UV‐initiated free‐radical/cationic dual curing technique. Final reactant conversions and photopolymerization rates of the hybrid UV‐cured coatings were improved with the increase of KH570 content, as evaluated by conversion profiles. The morphologies and microstructures were characterized by scanning electron micro‐scopic, atomic force micrographic, and fourier transform infrared spectrophotometer measurements. Thermal, mechanical, and surface properties of the hybrid UV‐cured coatings were investigated. The increase in KH570 content caused a decrease in mechanical properties besides the breaking elongation. Thermo‐gravimetric analysis revealed that the incorporation of silicon into cross‐linked network structure resulted in high thermal stability. The surface properties of hybrid UV‐cured coatings, such as hardness, contact angle, flexibility, and glossiness were also examined. It is found that transparent hybrid coating with the addition of 1.0 wt % KH570 exhibited a relatively higher contact angle as a direct result of a relatively higher hydrophobic surface. These researches showed that micro amounts of small molecular weight silicon‐containing acrylate could greatly influence the morphologies of liquid nitrogen quenching cross sections and properties of hybrid UV‐cured coatings and could be used to modify UV‐cured coatings for some superior properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40655.     

UV‐activated hydrosilation reaction for silicone polymer crosslinking

In this article hydrosilation was employed to achieve a fully cured three‐dimensional silicone network. The UV‐activated hydrosilation reaction was investigated focusing on the curing conditions and their relationships to physical properties. After finding the optimum catalyst concentration, it was observed that by decreasing the molecular weight of the vinyl oligomer a slight increase of the T_g value was achieved together with a complete suppression of the Tm. It was possible to fully cure samples up to 4 cm of thickness. The dark curing process was evaluated by FTIR analyses and it was evidenced an important increase on dark‐polymerization, which is dependent on the length of the UV‐irradiation time. This result shows the versatility of UV‐curing technique for silicone network formation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ultraviolet‐curing behavior of an epoxy acrylate resin system

Ultraviolet (UV)‐curing behavior of an epoxy acrylate resin system comprising an epoxy acrylate oligomer, a reactive diluent, and a photoinitiator was investigated by Fourier transform infrared (FTIR) spectroscopy. The conversion changes of the resin system containing 20 phr of 1,6‐hexanediol diacrylate as a reactive diluent and 2‐hydroxy‐2‐methyl‐1‐phenyl‐propan‐1‐one as a photoinitiator were measured under different UV‐curing conditions. The fractional conversion was calculated from the area of the absorption peak for the vinyl group vibration occurring at 810 cm^?1. The effects of photoinitiator concentration, total UV dosage, one‐step or stepwise UV irradiation, UV intensity, atmosphere, and temperature on the curing behavior of the resin system were investigated. The conversion of the resin system increased rapidly at the initial stage of the UV‐curing process but increased very slowly after that. The final conversion of the resin system was mainly affected by total UV dosage. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1180–1185, 2005     

Ultraviolet/heat dual‐curable film adhesives with pendant‐acryloyl‐functional‐group‐modified epoxy resin

To facilitate the fabrication of a reliable semiconductor package, the UV/heat dual curing of film adhesives was investigated. The curing system of the epoxy resin affected the film adhesive properties. As the UV/heat dual‐curable epoxy resin, a modified o‐cresol novolak epoxy resin, in which half of the glycidyl groups were substituted by acryloyl groups (OCN‐AE), was applied to the film adhesive. The formulated film adhesive contained acrylic copolymer, OCN‐AE, phenolic aralkyl resin as a heat‐curing agent of the glycidyl groups, and 1‐hydroxycyclohexyl phenyl ketone as a photoinitiator of the acryloyl groups. The formulated reference film adhesive contained unmodified o‐cresol novolak epoxy resin (OCN‐E) in place of OCN‐AE. Formulated film adhesives containing a mixture of OCN‐E and o‐cresol novolak epoxy acrylate were also used as references. The morphology and the film adhesive properties were investigated. In these investigations, the film adhesive of OCN‐AE showed better adhesive properties, lower modulus, and a better stress‐relaxation ability than the referenced adhesives. As a result, a reliable film adhesive for semiconductor packages was successfully developed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of partial cross‐linking degree on basic physical properties of RTM6 epoxy resin

Thermo‐physical and mechanical properties of partially and completely cross‐linked RTM6 epoxy resin samples in the glassy state have been investigated. A significant dependence of glass transition temperature, density, and modulus on the curing history and the curing degree is found. Density and modulus decrease with increasing curing degree and show a step‐like irregularity in the so called transition region, which is related to the transition from rubber to glassy state during cross‐linking and the starting of structural relaxation processes. The relationship between the thermo‐physical and mechanical properties, which is important for the development of new processing routes for fiber reinforced polymers, is addressed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4338–4346, 2013     

Investigating the surface properties of polyurethane based anti‐graffiti coatings against UV exposure

A permanent anti‐graffiti coating based on a polyurethane resin was prepared by incorporating different levels of an OH‐functional silicone modified polyacrylate additive. Static contact angle measurements and dynamic mechanical thermal analysis (DMTA) were employed to evaluate surface free energy and mechanical properties of the coating specimens, respectively. Effect of ageing condition on the graffiti properties of the coating samples was evaluated utilizing an accelerated weathering test. Color changes, surface morphology, and variations in the mechanical properties were also examined prior to and after being exposed to UV irradiation for 864 h in a QUV chamber. Results showed that surface free energy of the samples decreased with replacement of polyol with additive up to 5 mol %. A Scanning electron microscope equipped with energy dispersive X‐ray detector revealed that for the samples containing more than 5 mol % additive, there was an enrichment of silicone at the interface of films and air. At long exposure times and higher concentrations of additive, depreciation of graffiti properties was seen. DMTA and attenuated total reflectance‐fourier transform infra‐red studies before and after ageing showed that the silicone additive tended to degrade while it could cause an increase in crosslinking density. Water contact angles and atomic force microscopy images after ageing revealed that the cause of the depletion in anti‐graffiti properties was attributed to the deterioration of the silicone additive. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

UV‐curing and mechanical properties of polyester–acrylate nanocomposites films with silane‐modified antimony doped tin oxide nanoparticles

Antimony doped tin oxide (ATO) nanoparticles were used as nanofillers to improve mechanical properties of UV‐cured polyester–acrylate films. To improve the dispersion of ATO nanoparticles in the polyester–acrylate resin matrix and to strengthen interfacial interactions between ATO nanoparticles and the resin matrix ATO nanoparticles were first organically modified with 3‐methacryloxypropyltrimethoxysilane (MPS). The modification of ATO nanoparticles with MPS was confirmed by FTIR spectroscopy and thermogravimetric analysis (TGA). UV‐curing behaviors of the nanocomposites films were investigated by FTIR spectroscopy. Compared with the film with neat ATO nanoparticles, the film with the same amount of MPS‐modified ATO nanoparticles showed slightly higher UV‐curing rate and final conversion. The mechanical properties of the nanocomposites films were measured by universal testing machine. The MPS‐modified ATO nanoparticles could improve considerably the mechanical properties of the UV‐cured polyester–acrylate nanocomposites films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of UV weathering on the mechanical and antibacterial performance of peroxide‐cured silicone rubber containing biocide HPQM

2‐Hydroxypropyl‐3‐piperazinyl‐quinoline carboxylic acid methacrylate (HPQM) was used as a biocide in a silicone rubber compound. Antibacterial and mechanical performance of the compound was assessed before and after exposure to UV light for different times. Drop‐plate and halo tests were employed to evaluate qualitatively and quantitatively the antibacterial performance of the compound against Escherichia coli (E. coli, ATCC 25922) and Staphylococcus aureus (S. aureus, ATCC 25923). The results showed that the cure characteristics and the physical and mechanical properties of the HPQM‐containing rubber compound were strongly affected by the UV light. The tensile properties and hardness increased with UV aging. The lightness (L*) of the rubber compound without HPQM did not change with UV exposure, whereas that for the compound with HPQM decreased with UV exposure. The longer the contact time, the better the ability for killing the bacteria. After experiencing initial UV aging for 3 days, the rubber compound with HPQM showed an effective killing ability. However, after prolonged UV exposure, the antibacterial efficacy was reduced as a result of HPQM removal from the rubber surface during the condensation stage and a post‐curing reaction of the residual peroxide in the rubber compound. Under UV light, the silicone rubber compound with HPQM had a greater preference for killing the E. coli. J. VINYL ADDIT. TECHNOL., 20:49–56, 2014. © 2014 Society of Plastics Engineers     

Effect of multi‐walled nanotubes on the interlaminar shear strength of glass fiber/acrylate composite fabricated by stepwise ultra‐violet light curing

The interlaminar shear strength (ILSS) of glass fiber/acrylate composite with stepwise ultraviolet (UV) light curing was enhanced by adding multi‐walled carbon nanotubes (MWCNTs) into the resin matrix. The maximum content of MWCNTs that can be used in the process was investigated. Differential scanning calorimetry (DSC) results indicated that prepreg with MWCNTs of more than 0.5% by weight was difficult to cure by UV light because of its poor UV light penetration ability. The ILSS was improved obviously due to the improved resin toughness, crack propagation resistance and interfacial adhesion between the resin and glass fibers according to SEM images. Experimental results suggested that the addition of MWCNTs is an effective method to improve the ILSS of UV stepwise curing composites. POLYM. COMPOS., 38:2113–2118, 2017. © 2015 Society of Plastics Engineers     

Nano‐sio2‐reinforced ultraviolet‐curing materials for three‐dimensional printing

As an additive manufacturing technology, ultraviolet (UV)‐curing three‐dimensional printing, which requires the use of a photocurable resin, is increasingly being used to produce customized end‐user parts of many complex shapes. In this study, to improve the strength and ductility of printing materials, nano‐SiO₂‐reinforced photocurable resins were prepared by a planetary ball mill; then, the morphology, photochemistry, thermal property, and mechanical properties of the nanocomposites were investigated and characterized. Transmission electron microscopy analysis indicated that the modified nano‐SiO₂ was well dispersed in the photocurable resin. The glass‐transition temperature increased from 67.2°C for the unfilled resin to 71.7 and 80.1°C for nanocomposites with nano‐SiO₂ contents of 0.3 and 0.7 wt %, respectively. The tensile strength and impact strength were increased by 46.7 and 165.3% for nanocomposites with 0.3 wt % nano‐SiO₂. The flexural modulus of the nanocomposites increased from 1.7 to 8.0 GPa when 0.7 wt % nano‐SiO₂ was added to the photocurable resin; this appeared to originate from the relatively high level of dispersion and the intimate combination of the nano‐SiO₂ with the matrix. The investigation of the physical and chemical properties of such UV‐curing materials showed that the low filler concentration (<1 wt %) of nano‐SiO₂ did not affect the processability of the nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42307.     

Preparation and properties of transparent zinc oxide/silicone nanocomposites for the packaging of high‐power light‐emitting diodes

New transparent zinc oxide (ZnO)/silicone nanocomposites with outstanding integrated properties, including a high UV‐shielding efficiency and transparency, bigger thermal conductivity, and lower dielectric constant, were successfully developed; they were prepared by the uniform dispersion of organic modified nano‐ZnO in a silicone matrix through in situ polymerization. The ZnO precursor was prepared by a direct precipitation method, which was then calcinated at different temperatures to produce nano‐ZnO with various morphologies and sizes. The effects of the size, surface nature, and content of nano‐ZnO on the key properties (e.g., optical and dielectric properties, thermal conductivities) of the composites were systematically investigated. The results show that the organic nano‐ZnO prepared by 3‐methacryloxypropyltrimethoxysilane can increase the dispersion of nano‐ZnO in silicone resin, and the interfacial adhesion between inorganic and organic phases, and consequently improve the integrated properties of nanocomposites. The increase of the particle content and size of ZnO in composites can lead to high thermal conductivity and UV‐shielding efficiency but lower visible‐light transparency, so there is an optimum content and size of ZnO in composites to obtain the best integrated properties of the composites. Specifically, the nanocomposite containing 0.03 wt % organic nano‐ZnO with an average size of 46 ± 0.4 nm not only had a high visible‐light transparency, UV‐shielding efficiency, and thermal conductivity but also possessed a low dielectric constant and loss and met the requirements of high‐performance electronic packaging for high‐power light‐emitting diodes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ultraviolet‐curing behavior and mechanical properties of a polyester acrylate resin

Ultraviolet (UV) curing technology has been widely used in many applications because it has several distinct advantages compared to solvent‐based processes or thermal‐curing technology. The effects of photoinitiator types and their contents as well as reactive diluent types and their contents on the UV‐curing behavior and mechanical properties of a UV‐curable polyester acrylate resin were investigated in this study. Three photoinitiators, Irgacure 184, Darocur 1173, and benzophenone, were used in this study. Hexanediol diacrylate, tripropylene glycol diacrylate, and trimethylol propane triacrylate were used as reactive diluents to modify the properties of the acrylate resin. The change of chemical structure during UV curing was monitored by FTIR. A universal testing machine was used to measure the tensile properties of various UV‐cured acrylate films of different compositions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3921–3928, 2004     

Improving properties of ceramic silicone rubber composites using high vinyl silicone oil

Reactive high vinyl silicone oil (HVSO) was selected to prepare the ceramic silicone rubber composites. The effects of HVSO on the mechanical properties and thermal stabilities of ceramic silicone rubber composites were investigated. The structures of the cross‐linked network of silicone rubber with or without HVSO were studied. The intermolecular space of silicone rubber was enlarged, and the cross‐linked point was concentrated by addition of HVSO, which was demonstrated by cross‐linking densities, scanning electron microscope (SEM) images, and dynamic mechanical analysis (DMA). The cross‐linked network model was formed with the slipping of the cross‐linked points along with the silicone rubber chain. Mechanical properties of composites were enhanced by the formation of this cross‐linked network. The tear strength, tensile strength, and elongation at break of the composites were increased by 18.5%, 13.2%, and 37.4% by the adding of 2 phr HVSO, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41864.     

Investigation of polysiloxanes containing phenylethynyl groups as cross‐linkers of heat‐curable silicone rubber

Hydrosilation‐curing vulcanizates (HCV) and peroxide‐curing vulcanizates (PCV) were prepared respectively by using polysiloxanes containing phenylethynyl groups (PE‐PDMS) as cross‐linkers. The mechanical properties and average molecular weights of effective units (M̄_c) of HCV and PCV were measured. The experimental results show that PE‐PDMS can be used as cross‐linkers of heat‐curable silicone rubber instead of C gum, and when adding suitable amounts of PE‐PDMS, the vulcanizates exhibited good mechanical properties. The tear strength of some vulcanizates reached 30.0 kN/m, the tensile strength 11.7 MPa, the modulus at 100% extension 3.3 MPa, and the permanent deformation is low. PE‐PDMS also has cure retardation to hydrosilation‐cure silicone rubber and thus can prolong the shelf time of stocks. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1554–1557, 2000     

High‐temperature‐resistant polymer gel system with metal–organic mixed cross‐linking agents

A high‐temperature (200°C)‐resistant polymer gel system was developed from partially hydrolyzed polyacrylamide (HPAM), chromium lactate (CrL), and water‐soluble phenol/formaldehyde resin (WPF) mixed cross‐linkers. Rheological measurements indicated that the gelation process of the gel system could be divided into four successive steps: induction, first cross‐linking with metal cross‐linker, secondary cross‐linking with organic cross‐linker, and stabilization. Effects of various parameters that affect the gelation time and gel strength including polymer concentration, cross‐linker concentration, salinity, pH, and the gelation temperature were evaluated. Gelant formulated with 0.5 wt % HPAM, 0.1 wt % CrL, and 0.9 wt % WPF and treated at 80°C for 48 h showed sufficient gelation time, high rigidity, and good thermal stability. Morphology observation by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the gel had compact network microstructure. A cross‐linking mechanism for the gel system was proposed based on the gelation process and experimental results. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42261.