Polyurea Formaldehyde Research Articles

Amino-silane surface modification of urea-formaldehyde microcapsules containing linseed oil for improved epoxy matrix compatibility. Part I: Optimizing silane treatment conditions

In microcapsule-filled self-healing coatings, a good microcapsule/matrix interface improves repairing performance by directing the crack through the microcapsule and releasing the core material. In this study, the surface of the synthesized linseed oil filled polyurea-formaldehyde (PUF) based microcapsules was treated with 3-aminopropyltrimethoxy silane (APS, via a two-step sol-gel route), in order to improve its interface with an epoxy coating. The treated microcapsules were then characterized using various characterization techniques. The effect of silane treatment on the microcapsule/matrix interface and tensile properties of the coating was evaluated.FTIR spectroscopy showed both physical and chemical interactions between APS and PUF microcapsules. SEM micrographs revealed an almost spherical morphology for both treated and un-treated microcapsules. TGA results showed that the maximum silane grafting occurs at pH 7.5. It was found that the addition of APS-treated microcapsules had a positive effect on the tensile properties of the coating due to improving microcapsule’s shell and polymer matrix compatibility. This was related to the reaction of hydroxyl groups on PUF microcapsules and silanol groups of the silane and the subsequent reaction of amine group of the silane with the epoxy group of the coating.

Effect of Incorporation of Self-Healing Microcapsules to Experimental Resin Composite on Some Mechanical Properties

Purpose: The present study aimed to investigate the effect of incorporation of the new Triethylene glycoldimethacrylate and N,N-Bis(2-hydroxyethyl)-p-toluidine (TEGDMA)- (DHEPT) in polyurea formaldehyde (PUF) micro-capsules into an experimental dental resin composite on the flexural strength and fracture toughness and the evaluation of its self- healing efficacy. Materials and Methods: Polyurea formaldehyde microcapsules were synthesized by insitu polymerization technique, encapsulating a triethylene glycol dimethacrylate and dihydroxy ethyl para toluidine (TEGDMA–DHEPT) as a healing liquid, then experimental composite resin is prepared. Microcapsules are incorporated in the resin composite with concentrations 0%, 2.5%, 5%, 7.5% and 10%, then experimental resin composite specimens were fabricated. Fracture toughness and flexural strength were examined by three point loading using universal testing machine till fracture. The fracture toughness was evaluated by using single edge V-notched beam method, self healing efficacy is evaluated as the ratio between the healed fracture toughness and the virgin fracture toughness. Results: Regarding flexural strength results, it was found that the 0% group has the highest flexural strength while the 10% group had the lowest flexural strength. On the other hand, on evaluating the results, of 7.5% group it was found that this concentration did not affect the flexural strength remarkably. Regarding the virgin fracture toughness results, 0% group has the highest flexural strength, while the 10% group the lowest flexural strength, specimens were fractured and healed, then fractured again to measure the healed fracture toughness, on examining the results of the healed fracture toughness, it was found that no significant difference between 0% and 2.5% as no healing occur at such specimen, Also the results showed that the highest healed fracture toughness was in 5%, followed by 7.5%, followed by 10%. The self-healing efficacy increased to a recovery of about 75% in KIC when the microcapsule mass fraction was increased from 5% to 7.5% till reaching 10% concentration. Conclusions: In light of restoration fracture as one of the primary failure reasons, the novel self-healing dental composite may be promising to heal crack damages and to prolong the durability of the restoration clinically.

Evaluation and failure analysis of linseed oil encapsulated self-healing anticorrosive coating

In this study, a linseed oil encapsulated self-healing coating was developed by incorporating 10 wt% synthesized microcapsules into an epoxy-polyamine coating matrix. The linseed oil encapsulated polyurea-formaldehyde (PUF) microcapsules had ∼80 wt% core content with ∼80 um diameter. The influence of embedded microcapsules on the anticorrosive property of the self-healing coating had been studied by electrochemical impedance spectroscopy. The intact self-healing coating exhibited excellent anticorrosive property as the intact pure epoxy coating, although the addition of microcapsules into the epoxy matrix resulted in a higher water-uptake. The scratched self-healing coating showed excellent healing ability and corrosion inhibition function for microcracks, but it still cannot recover the barrier property as good as the intact coating. The failure of the scratched self-healing coating had been analyzed and the possible reason may be the formation of conductive pathways at the interface between the linseed oil film and the epoxy matrix and/or PUF microcapsule shell.

Adsorptive removal of noxious cadmium from aqueous solutions using poly urea-formaldehyde: A novel polymer adsorbent

Cadmium is a heavy metal toxic that enters water resources through industrial, household, agricultural waste and non-sanitary landfill of urban and industrial wastes. Pollution of water resources by cadmium increases incidence of diseases including Itai-Itai, kidney disorders, cancer, chromosome effects and kidney tubular damages in low exposures. The aim of this study is to study the efficiency of a new poly urea-formaldehyde adsorbent in the removal cadmium ions from aqueous solutions. The effect of different variables such as initial pH, contact time, initial concentration of cadmium and test of real wastewater samples were evaluated. In addition, laboratory data of cadmium adsorption by urea-formaldehyde adsorbent were matched to Langmuir, Freundlich and Temkin isotherm models. The results of the study showed that maximum adsorption capacity obtained by Langmuir model was 76.3?mg/g at pH?=?5.5. Laboratory adsorption data matched mostly by Freundlich isotherm model (R2 =0.999) which indicates that adsorption of cadmium ions on heterogenic surfaces of poly urea-formaldehyde happens by chemical adsorption mechanism. Generally, the results of the study showed that new poly urea-formaldehyde adsorbent can be efficiently used to remove highly concentrated cadmium ions from aqueous solutions.

Acoustic characterization of damage and healing of microencapsulation-based self-healing cement matrices

Self-healing of cracks in cementitious composites is of great significance to improve the serviceability of concrete structures. In this study, poly urea–formaldehyde (PUF) microcapsules enclosing epoxy resins were synthesized. The damage- and healing process of cement paste incorporating microcapsules was in situ detected by acoustic emission (AE) technique, in which passive AE and active AE were combined to provide complementary information about the damage and crack formation. The two representative AE signals, i.e., matrix cracking and debonding of the interface, were used as calibration for further AE post-processing analysis. The effects of the concentration of microcapsules and the level of pre-damage were investigated. The results revealed the distinguished cracking mechanisms according to the differentiated feature of the signals in terms of the temporal and spectral AE descriptors. The plot of average frequency (AF) versus RA index (rise time/amplitude) confirms that the cracking modes contribute to the characteristic spectrum.

Adsorption of Mefenamic Acid From Water by Bentonite Poly urea formaldehyde Composite Adsorbent

Poly urea formaldehyde –Bentonite (PUF-Bentonite) composite was tested as new adsorbentfor removal of mefenamic acid (MA) from simulated wastewater in batch adsorption procedure. Developed a method for preparing poly urea formaldehyde gel in basic media byusing condensation polymerization. Adsorption experiments were carried out as a function ofwater pH, temperature, contact time, adsorbent dose and initial MA concentration .Effect ofsharing surface with other analgesic pharmaceuticals at different pH also studied. Theadsorption of MA was found to be strongly dependent to pH. The Freundlich isotherm modelshowed a good fit to the equilibrium adsorption data. From Dubinin–Radushkevich model themean free energy (E) was calculated and the value of 5 KJ/mole indicated that the mainmechanism governing the adsorption of MA on PUF-Bentonite composite was physical innature. The kinetics of adsorption tested for first order, pseudo second order models andElovich’s equation, results showed the adsorption followed the pseudo-second-order model.

Preparation of Microcapsules Containing Benzoyl Peroxide Initiator with Gelatin-Gum Arabic/Polyurea-Formaldehyde Shell and Evaluating Their Storage Stability.

This work involves the optimized preparation and characterization of microcapsules which contain benzoyl peroxide (BPO) dispersed in dibutyl phthalate (DBP) with gelatin-gum arabic (Gel-GA)/polyurea-formaldehyde (PUF) shell. The microcapsules were prepared in two steps using complex coacervation and in situ polymerization techniques, respectively, at various mixing speeds and different core:shell ratios. The scanning electron microscopy (SEM), optical microscopy, and Fourier transform infrared (FTIR) spectroscopy were used for characterization of prepared microcapsules. The resultant microcapsules were spherical with average diameters about 120-200 μm, had no intercapsule bonding, and had thicknesses of 0.7-1.5 μm. The results revealed high core content loading, 82-89 wt % for microcapsules prepared at various mixing speeds. The differential scanning calorimetry analysis (DSC) indicated that the encapsulated BPO was not influenced by the encapsulation process and maintained its activity. Moreover, with a compact and double Gel-GA/PUF shell, the microcapsules were stable, and no leakage of core material in an acrylate-based resin and toluene as an organic solvent was recorded. The resultant microcapsules have the potential of usage in industries such as self-healing systems and structural adhesives where the impermeability of microcapsules is an important factor.

Effects of Preparation Conditions on the Yield and Embedding Ratio of Vinyl Silicone Oil Microcapsules

Self-healing materials could repair themselves without external influences when they are damaged. In this paper, microcapsules are prepared by in-situ polymerization method with vinyl silicone oil as core material, polyurea formaldehyde (PUF) as wall material and polyvinyl alcohol as dispersants. The morphology and structure of the microcapsules are tested with scanning electron microscopy (SEM), polarizing microscope（PM）and laser particle analyzer(LPA). Effect of the reaction temperature, stirring speed and PVA concentration on the yield, embedding ratio, particle size and distribution of the microcapsules are studied. Results show that the microcapsules can be successfully prepared by in situ polymerization method. When the reaction temperature was 60℃, the stirring speed 1000 r/min, dispersant concentration 0.1%, the yield and embedding ratio of the microcapsule are 52.5% and 50.1%. The microcapsules prepared have smooth surface, well dispersibility, narrow particle size distribution and the average particle size is 13 μm.DOI: http://dx.doi.org/10.5755/j01.ms.22.2.13026

Self-healing of polystyrene block–polyisoprene block–polystyrene

The addition of self-healing properties to polystyrene block–polyisoprene block–polystyrene by loading the polymeric matrix with microcapsules filled with monomer [dicyclopentadiene (DCPD)] and first generation Grubbs catalyst is described in detail. The confinement of DCPD in polyurea formaldehyde microcapsules has been demonstrated by Raman spectroscopy. The above mentioned components (polymeric matrix, microcapsules filled with monomer and catalyst) have been mixed in solution, and the solvent has been slowly evaporated. The polymerisation of the monomer (DCPD) within the self-healed polymeric system after the fracture of microcapsules has been confirmed by Raman spectroscopy. Slow stress–strain mechanical testing has confirmed the efficiency of the added self-healing capabilities.