UF microcapsules

Such a product would bait or lure a pest to a capsule, but release the pesticide only when the pest digests or attacks the capsule. Using this method, UF microcapsules containing pesticide were prepared such that the capsule size was very small (-15 pm). The second wall material is formed by mixing appropriate amounts of gelatin, gum arabic, and ethyl cellulose in water. UF microcapsules mixed with peanut oil (as attractant) are added to the second wall material solution which, after stirring for 1 h at 65 °C, was cooled to room temperature and stirred for another hour. The resultant gelatin-based shell material encapsulated both peanut oil and UF microcapsules. 

UF microcapsules containing orange or rose extracts are reported to be most suitable for nonwoven fabrics due to their open structures [57]. Microcapsules containing perfume prepared by coacervation methods using gelatin and gum arable have been reported to be useful in solid soap composition. The perfume is released when the soap is placed in contact with water during use [58]. 

UF microcapsules containing DCPD have been prepared by in-situ polymerization in an oil-in-water emulsion [66]. Different experimental parameters such as agitation speed, temperature and pH have been studied in order to obtain microcapsules with a long shelf-life - that is, microcapsules which are impervious to leakage and diffusion of the encapsulated (liquid) heahng agent for a considerable time. 

Spherical UF microcapsules of quinolphos, prepared with different degrees of crosshnldng and varying in terms of the weight ratios of urea to melamine, have been found to be quite stable as dry powders [11,12]. Quinolphos is commercially... 

Poly(urea-formaldehyde) (UF) microcapsules prepared by in situ polymerization of urea and formaldehyde meet the demanding criteria required for use in self-healing materials (Suiyanarayanaa, 2008). These criteria includes excellent bonding to the matrix, sequestration of the healing monomer fiom the surrounding environment, and rapture and release of the monomer into the crack plane upon matrix damage (Blaiszik B. J., 2009). 

Figure 6. ESEM image of (a) UF microcapsules loading in TMPTA monomer and Darocur 1173 photomitiator with a smooth surface, (b) UF microcapsules loading m TMPTA monomer and Darocur 1173 photoinitiator with a rough surface and (c) ESEM image of ruptured Urea-Formaldehyde microcapsule...

Infrared Analysis - The comparison between infrared spectra of UF empty microparticles -Figure 7 (a) and UF microparticles loaded in TMPTA - Figure 3 (b), shows the presence of new bands, in particular at 1722 cm (C=0 stretching vibration), 983 cm (wagging of the =CH2 group), and 808 cm i (twisting of the =CH2 group), characteristic bands of TMPTA which indicates that this compound has been encapsulated in UF microcapsules. 

Figure 7. Infrared spectrum of (a) Empty UF microcapsules, (b) broken UF microcapsules loaded with TMPTA and (c) TMPTA monomer...

Thermogravimetric Analysis - Empty UF microcapsule shows - Figure 8, a weight loss (around 10 %) until 110 °C corresponding to the evaporation of free water in microcapsules, and an important decreasing in weight (around 80 %) starting from 180 °C due to the decomposition of urea-formaldehyde microparticles. Therefore the urea formaldehyde could not be used to self-heal spatial device composites because of polymer decomposition below 300 °C (maximum temperature in space). 

Lampiecht A, Schafer UF, Lehr CM. Visualization and quantification of polymo- distribution in microcapsules by confocal laser scanning microscopy (CLSM). hit J Pharm 2000 196(2) 223-226. 

Zhao, D. Liu, F. Mu, W. Han, Z.-R. Factors affecting morphology and encapsulation ratio of chlorpy-rifos microcapsules with UF-resin during preparation. Yingyong Huaxue (2007), 24(5), 589-592. 

The properties of supported enzyme preparations are governed by the properties of both the enzyme and the carrier material. The interaction between the two provides an immobilized enzyme with specific chemical, biochemical, mechanical and kinetic properties. The support (carrier) can be a synthetic organic polymer, a biopolymer or an inorganic solid. Enzyme-immobilized polymer membranes are prepared by methods similar to those for the immobilized enzyme, which are summarized in Fig. 22.7 (a) molecular recognition and physical adsorption of biocatalyst on a support membrane, (b) cross-linking between enzymes on (a), (c) covalent binding between the biocatalyst and the membrane, (d) ion complex formation between the biocatalyst and the membrane, (e) entrapment of the biocatalyst in a polymer gel membrane, (f) entrapment and adsorption of biocatalyst in the membrane, (g) entrapment and covalent binding between the biocatalyst and the membrane, (h) entrapment and ion complex formation between the biocatalyst and the membrane, (i) entrapment of the biocatalyst in a pore of an UF membrane, (j) entrapment of the biocatalyst in a hollow-fiber membrane, (k) entrapment of biocatalyst in microcapsule, and (1) entrapment of the biocatalyst in a liposome. 

The appeal of DCPD and ENB for self-healing has led to the development of several encapsulation techniques for these monomers. Most prominent techniques consist of forming a shell material around monomer droplets by in situ polymerization of an amino resin melamine-urea-formaldehyde (MUF, Figure 10.2a) [56], urea-formaldehyde (UF, Figure 10.2b) [13-16], or melamine-formaldehyde (MF) [17, 18] walls in an oil-in-water emulsion. Comparison of microcapsules made with different shell wall materials is challenging because... 

Figure 10.2 Assortment of microcapsules containing ROMP-based healing monomers, (a) ENB in a MUF shell, (b) ruptured UF shell embedded in a fracture surface, and (c) nanocapsules containing DCPD in a UF shell. Reprinted with permission from Refs. [3, 23, 56].

Scanning Electron Microscopy was performed to analyze surface morphology and shell wall thickness of the capsule. A dried microcapsule was placed on a conductive carbon tape attached to a mounting piece for imaging. Few microcapsules were mptured with a razor blade to confirm the presence of alkyd resin inside the UF shell. 

Thermal analyses of microcapsules were carried out to prove encapsulation of alkyd resin inside UF Shell. The TGA of microcapsule is done and the curve is shown in Figure 3. The first endothermic peak at 229.2°C corresponds to UF decomposition temperature (Siuyanarayanaa et al., 2008) and the endothermic peak at 350°C corresponds to the start of alkyd resin decomposition temperature which ends at 450.5°C. These results establish that microcapsules contain alkyd resin as core and UF resin as the shell. The weight loss of the sample was found to be 4.5 mg (98.11%)... 

The DSC curve of the microcapsule is shown in Figure 4. The endothermic peak at 115.7°C corresponds to melting of UF resin and at 199.4°C corresponds to melting of alkyd resin whereas at 147.4°C it corresponds to evaporation of solvent xylene. Deviations in the base line are said to be glass transition temperature... 

Alkyd resin along with solvent has been successfully encapsulated inside UF shell by In situ encapsulation technique. The SEM analysis shows that microcapsules were comprised of a thin continuous shell wall and a rough exterior shell wall. The FTIR spectra of original and soxhlet extracted resin proves the encapsulation of alkyd resin inside the shell. Moreover DSC and TGA analysis shows that the microcapsules contain both resin-solvent mixture as core and UF as shell material. These microcapsules incorporated in paints or coatings release the healing material when scratched which in turn heals the scratches and cracks. 

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