Reinforced plastic canal and pipe linings

Presented at Irrigation and water resources in the 1990's: proceedings from the 1992 national conference held on October 5-7, 1992 in Phoenix, Arizona.Includes bibliographical references.Unlined canals and ditches seep, erode, and present management problems. Over time concrete lined canals crack and deteriorate. Pipelines and culverts crack, corrode, leak, and function poorly. A problem solution for unlined canals is to install a reinforced plastic lining which is cheaper, more watertight, and more durable than concrete. For deteriorating concrete canals a reinforced plastic lining can be applied to the existing surface. A reinforced plastic liner can be installed in deteriorating pipelines or culverts. water control structures can be rehabilitated. These measures can be accomplished with a process and machine which mixes and assembles raw materials (plastic components and reinforcing fabric) at the job site, and applies this composite to the surface of a canal, ditch, pipeline, or structure. As the plastic cures it adheres to the underlying surface and creates a reinforced lining. The plastic used can be formulated to fit the requirements of the particular situation. The lining is durable, water tight, and does not have to be earth covered. The lining can be laid in continuous overlapping strips across large canals, or along the length of small canals. Deteriorating pipelines can be lined using an inflatable bladder surrounded by the plastic composite. This paper explains the process and gives examples of its use

Characterisation and Skin Distribution of Lecithin-Based Coenzyme Q10-Loaded Lipid Nanocapsules

The purpose of this study was to investigate the influence of the inner lipid ratio on the physicochemical properties and skin targeting of surfactant-free lecithin-based coenzyme Q10-loaded lipid nanocapsules (CoQ10-LNCs). The smaller particle size of CoQ10-LNCs was achieved by high pressure and a lower ratio of CoQ10/GTCC (Caprylic/capric triglyceride); however, the zeta potential of CoQ10-LNCs was above /− 60 mV/ with no distinct difference among them at different ratios of CoQ10/GTCC. Both the crystallisation point and the index decreased with the decreasing ratio of CoQ10/GTCC and smaller particle size; interestingly, the supercooled state of CoQ10-LNCs was observed at particle size below about 200 nm, as verified by differential scanning calorimetry (DSC) in one heating–cooling cycle. The lecithin monolayer sphere structure of CoQ10-LNCs was investigated by cryogenic transmission electron microscopy (Cryo-TEM). The skin penetration results revealed that the distribution of Nile red-loaded CoQ10-LNCs depended on the ratio of inner CoQ10/GTCC; moreover, epidermal targeting and superficial dermal targeting were achieved by the CoQ10-LNCs application. The highest fluorescence response was observed at a ratio of inner CoQ10/GTCC of 1:1. These observations suggest that lecithin-based LNCs could be used as a promising topical delivery vehicle for lipophilic compounds

Crystallization tendency and polymorphic transitions in triglyceride nanoparticles

The ability of tristearin, tripalmitin, trimyristin and trilaurin to form solid lipid nanoparticles after melt-homogenization is investigated by DSC and X-ray diffraction. Upon storage at common temperatures after preparation solid nanoparticles are formed in tristearin and tripalmitin dispersions. In contrast to literature reports, colloidal dispersions of trilaurin do not form solid particles under those conditions. They should, therefore, be regarded as emulsions of supercooled melts rather than as nanosuspensions. Trimyristin nanoparticles which can be obtained in solid or liquid form have a larger incorporation capacity for the lipophilic model drug menadione in the liquid than in the solid state. The kinetics of polymorphic transitions after crystallization of triglyceride nanoparticles are slower for longer-chain than for shorter-chain triglycerides. Addition of tristearin raises the crystallization temperature of colloidally dispersed trimyristin and trilaurin facilitating solidification during production. The structure and melting behavior of the resulting mixed nanoparticles are more complex than those of nanoparticles prepared from the simple triglycerides. Depending on the mixing ratio, the time-course of polymorphic transitions after crystallization may also be altered significantly. The melting enthalpy of the mixed nanoparticle dispersions is usually not significantly different from that of dispersions of the simple triglycerides

Physicochemical characterization of lipid nanoparticles and evaluation of their drug loading capacity and sustained release potential

Drug carrier systems based on lipid nanosuspensions prepared by melt emulsification present a number of severe stability problems such as a high gelation tendency, considerable particle growth and drug expulsion. Destabilization of the emulsified lipidic carriers is related to recrystallization of the lipids. The choice of stabilizers for colloidal lipid suspensions is, therefore, restricted. Systematic surface modifications are thus limited. In addition, the drug payload of crystalline nanosuspension particles is generally low. Improved stability and loading capacities were found for amorphous lipid nanoparticles which present the characteristic signals of supercooled melts in high resolution 1H-NMR. The NMR data indicate that such liquid but viscous carriers can, however, not immobilize the incorporated drug molecules to the same extent as a solid matrix. Sustained release over days or weeks as in slowly biodegraded solid matrices thus seems difficult to achieve with a supercooled melt. Attempts to combine the advantages of the solid crystalline lipids and the amorphous nature of the supercooled melts by generating solid but amorphous lipid suspension particles with a satisfactory long-term stability by a variation of the lipid matrix material have hitherto not been successful. Even a satisfactory stabilization of the α-modification using complex lipid mixtures to improve the loading capacity or to slow down the drug expulsion process could not be achieved. The rates of the polymorphic transitions were much higher in the colloidal lipid dispersions than in the bulk for the hard fats under investigation. Despite the fact that the properties of the lipids are superimposed with colloidal properties, significant differences between monoacid triglycerides and complex lipids were, however, found

Characterization of Native and Drug‐Loaded Human Low Density Lipoproteins

Low‐density lipoproteins (LDLs), the physiological vehicles for lipids, are potentially useful drug delivery devices for (hydrophobic) drugs. The physcochemical characteristics of LDL loaded with the adriamycin derivative AD 32 or the N‐mustard derivative WB 4291 were compared to that of native and reconstituted LDL at different temperatures. X‐ray solution scattering indicates that loading with AD 32 has no detectable effect on the particle structure at room temperature, in contrast to WB 4291. According to 19F NMR data, AD. 32 molecules are located in two distinct chemical environments with restricted motional freedom of the CF3 groups in samples stored as lyophilisates. 1H NMR signals from AD 32 were not observed, while those from WB 4291 could be distinguished from those of LDL constituents. WB 4291 molecules are in an environment with a higher motional freedom than AD 32 molecules. 1H NMR data suggest a higher fluidity of the core components for the WB‐loaded LDLs compared to the other LDL preparations. While the motional freedom of the phospholipid head groups seems to be temperature independent, there is an increase in the mobility of the lipid components in the core region of the LDL particles with temperature

Phase Behavior of Tyloxapol/Triton X100/Water Mixtures

The influence of admixture of Triton X100 to the polymer tyloxapol and the phase behavior of the mixtures in contact with water was investigated by viscometry, polarization microscopy, and X‐ray scattering. The viscosity of tyloxapol/Triton X100 mixtures is lower than that of pure tyloxapol. With increasing Triton X100 content, the phase behavior of the surfactant mixtures in contact with water evolves from the complex behavior of tyloxapol to the simpler one of Triton X100. In contact with water, mixtures rich in tyloxapol form hexagonal, cubic, and lamellar lyotropic liquid crystalline phases over a wide range of concentration and temperature, whereas Triton X100/water mixtures form only a hexagonal phase in a limited concentration and temperature range. The polymeric nature of tyloxapol stabilizes the liquid crystalline structures, and the size of the supramolecular structures in the water‐containing surfactant systems is independent of the tyloxapol/Triton X100 mixing ratio but depends highly on water content. The ability of tyloxapol to form stable lyotropic liquid crystalline phases at body temperature, which has been proposed as a basis for the development of novel peroral sustained‐release systems, is not significantly impaired by the addition of appropriate amounts of Triton X100. Admixture of Triton X100 to tyloxapol may thus provide a way to circumvent processing problems during the preparation of pharmaceutical formulations based on the highly viscous tyloxapol