Measurement of release rates of gossyplure from controlled release formulations by mini-airflow method

The use of the mini-airflow apparatus for the measurement of gossyplure release rates is described. The method involves the passage of air over controlled-release dispensers containing radiolabeled pheromone, through a coarse frit, and entrapment of the gossyplure on glass beads. Desorption of the beads with solvent is followed by quantification by liquid scintillation counting. The results of release rate measurements from hollow fibers, red rubber septa, and red rubber wicks are discussed.     

A vapor collection and thermal desorption method to measure semiochemical release rates from controlled release formulations

Chemicals (bp 270–490 °C/1 atm) evaporated from a controlled-release formulation dispenser were carried by an airflow to a collector packed with a polymeric adsorbent. After a set time, the chemicals were recovered by thermally desorbing them onto a gas-liquid chromatograpic column. They were then separated and quantified. The apparatus is described, and the requirements for its successful use are discussed. The soundness of the thermal desorption technique was confirmed by comparison with another technique: solvent elution from the collector. The advantages of the former technique are discussed.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of that product by the USDA.     

Release rates of tetradecen-1-ol acetates from polymeric formulations in relation to temperature and air velocity

An apparatus was developed for investigating the release rates of pheromone formulations at temperatures and air velocities that correspond with those in the field. Polyurethane foam proved an excellent adsorbent for the recovery of tetradecen-1-ol acetates, allowing high air flows at low differential pressure and without breakthrough of these compounds. The experimental setup and procedures are described. The release rates of all formulations investigated were almost proportional to the square root of air velocity, and their logarithms were proportional to the reciprocal of temperature (K). When temperature is increased from 15°C to 25°C, the release rates increase by about 2-2.5 ×. Both relationships were combined into one equation that allows a reliable estimate to be made of the actual release rates of a formulation, under varying conditions, on the basis of its specific parameters and the relevant meteorological data.     

Commercial hollow-fiber pheromone formulations: The degrading effect of sunlight on celcon fibers causing increased release rates of the active ingredient

The effect of weathering on the release of pheromone analogs from Celcon fibers has been studied. Results from fibers exposed in Quebec indicate that UV radiation in sunlight degrades the Celcon, causing an increase in the release of the active materials. The results are discussed in the light of large interfiber release rate variation experienced with commercial fiber formulations, and the fact that the major use areas, to date, have been Arizona and California where the effect is likely to be much more pronounced. Stability of the release device to weathering is shown to be one of the many parameters to be considered in formulation design.Contribution No. 412, Department of Biology, Laval University.     

A temperature-dependent model for predicting release rates of pheromone from a polyethylene tubing dispenser

A model was developed to describe release of two formulations of tetradecenyl acetates in Shin Etsu polyethylene tubing pheromone dispensers. Change in pheromone column length in the polyethylene tubing was modeled bydl/dt=l ... (a+bT)/dt (wherel is column length,t is time interval, andT is average temperature for that time interval). Regression of the natural log of relative change in liquid length against time interval and accumulated day degrees in orchards produced the coefficientsa andb. The model was validated by comparing predicted and actual liquid length remaining in field-aged dispensers, as well as measuring release rates by using gas chromatography. Mean daily orchard temperatures and measurement of column length of dispensers on a single date were used to accurately predict column length within 15%, after six months. Predictions of instantaneous release rate were also made from this model, and other possible model uses and limitations are discussed.     

Comparison of release behaviour from microcapsules and microspheres

The plasticizing effect of core oil in the polymer shell of core–shell particles, so-called microcapsules, was here examined. The study involved release measurements of 4-nitroanisole into aqueous solution from two types of microparticles. In the first study, a microcapsule with PMMA shell and hexadecane core was examined. The second type of particle was a homogeneous PMMA microsphere containing no oil. Experimental data were compared to models that describe release by a diffusion mechanism out from core–shell particles as well as homogeneous spherical particles. Results clearly show that the alkane oil has a plasticizing effect on the PMMA shell, thereby generating a faster release of 4-nitroanisole. In both types of microparticles, the diffusion coefficients of 4-nitroanisole could be determined. The findings increase our understanding of important parameters in the microcapsule design with regard to tuning the release behaviour. Using microparticles, the ambition is to prolong the protection of paint and other coatings against fouling.     

Molecular release from painted surfaces: Free and encapsulated biocides

The current standard way of using biocide in coatings for protection against micro-organic surface growth, so called biofouling, is insufficient as the biocide leaks out from the coating too fast. In this article, we investigate a method for prolongation of the coating protection by slowing down the release rate of biocides in a controlled way. The biocide is placed into micrometer-sized reservoirs, called microspheres, from where it is slowly distributed into the coating. By different microscopic techniques the microspheres were found to be compatible (i.e. no phase separation was observed) both with the coating material and the paint. Biocide release from the coating is recorded by liquid scintillation counting and it was clear that the release is considerably slower from coatings with microspheres compared to an ordinary formulation with freely dispersed biocides. Microspheres might thus be a beneficial tool for the development of coatings with a longer protection against biofouling.     

Temporal patterns of sex pheromone titers and release rates inHolomelina lamae (Lepidoptera: Arctiidae)

Six hydrocarbon components (2-methylhexadecane,n-heptadecane, 2-methylheptadecane, 2-methyloctadecane,n-nonadecane, and 2-methylnonadecane) were identified in sex-pheromone gland extracts and in airborne collections ofHolomelina lamae. Low variability in the ratio of components among individuals indicates tight regulation of blend composition. Minor changes were evident in the quantity and ratio of the blend as a function of time of day. Based on gland extracts, the total quantity of the six components increased from day 1 (X = 6299 ng) to day 4 (X = 7498 ng) and subsequently decreased. No significant correlations were found between total gland contents and wet or dry weights of moths. Emission rates ofH. lamae females were determined from pheromone adsorbed onto Porapak Q. Quantities released peaked shortly after the onset of calling and decreased rapidly as calling continued. Peak release rates ranged from 13 to 350 ng/10 min, and from 37 to 835 ng/60 min. Noncalling females did not emit detectable quantities of pheromone. Based on release rates and the rate of pulsation of the abdominal tip, the average amount released per pulse is not constant. The mean ratio of components released (0.787.45 84.802.842.591.53) was not very different from the ratio of components in gland extracts of 2-day-old females (0.704.1990.12 1.651.911.42). We propose that the blend is atomized rather than volatilized from the gland, thus retaining nearly the same ratios in the female's effluvium as in her gland.     

Synthesis of biodegradable thermo- and pH-responsive hydrogels for controlled drug release

Novel intelligent hydrogels composed of biodegradable and pH-sensitive poly(l-glutamic acid) (PGA) and temperature sensitive poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (PNH) were synthesized and characterized for controlled release of hydrophilic drug. The influence of pH on the equilibrium swelling ratios of the hydrogels was investigated. A higher PNH content resulted in lower equilibrium swelling ratios. Although temperature had little influence on the swelling behaviors of the hydrogels, the changes of optical transmittance of hydrogels as a function of temperature were marked, which showed that the PNH part of hydrogel exhibited hydrophobic property at temperature above the lower critical solution temperature (LCST). The biodegradation rate of the stimuli-sensitive hydrogels in the presence of enzyme was directly proportional to the PGA content. Lysozyme was chosen as a model drug and loaded into the hydrogels. The in vitro drug release experiment was carried out at different pH values and the release data suggested that both the pH and PNH content played important roles in the drug release behaviors of the hydrogels.     

Slow release rate: Individual granules and population behaviour

Individual granules within a given granule population of a slow-release fertilizer (SRF) have a different release pattern. The populations studied differed both in relation to the time delay before the start of the release process and to the duration of the release. An association between a short delay period and a rapid release was found.The random reease distribution can be approximated using first-order rate equations. In cases, a term describing a lag period should be added.The distribution of release timing among the fertilizer granules may allow a long-lasting nutrient supply to the plant, as long as there are enough granules within the root zone to allow a uniform supply pattern.     

Novel diffusion-dilution method for release of semiochemicals: Testing pheromone component ratios on western pine beetle

Each of the pheromone components of the Western pine beetle,Dendroctonus brevicomis LeC. (Coleoptera: Scolytidae), exo-brevicomin (E) and frontalin (F), were released in the forest at various ratios 0.011, 0.11, or 11 to a constant dose of the opposite component (E or F) plus the host monoterpene myrcene (M), which were each released at 1.5 mg/day. The components were released by a new method that combines the principles of chemical diffusion through a tube with mole percentage dilution of the chemical. Both sexes ofD. brevicomis were attracted similarly at comparable ratios (and release rates) of E or F and showed similar logarithmic relationships (r ²=0.920.99). The bark beetle predator,Temnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae) was apparently less sensitive to E thanD. brevicomis, being relatively less attracted to amounts of E equivalent to that released by 70 females, while none were attracted to that from seven females (while this rate still attracted significant numbers of conspecifics). The apparent insensitivity of bark beetles to extreme ratios between pheromone components in contrast to moths is discussed. The advantages of the diffusion-dilution method of releasing semiochemicals compared to previous methods of absorbents, wicks, capillary tubes, and semipermeable plastic membranes are also discussed.     

Controlled release of biocide from silica microparticles in wood paint

Porous microparticles represent an attractive encapsulation platform as they provide a feasible route to a wide range of encapsulated chemical compounds. This assures an increased lifetime of the encapsulated compound by protecting it from the surrounding environment as well as providing a way to control the release rate. Porous microparticles encapsulating the commonly used biocide for wood protection, 3-iodoprop-2-ynyl N-butylcarbamate (IPBC), have been synthesized. The microparticles are spherical with an average size distribution of roughly 1 μm as determined by scanning electron microscopy (SEM). Determination of the release rate of the biocide from microcapsules incorporated into the paint film has been performed under diluted conditions. These experiments show that a slower release of the biocide can be obtained by encapsulation. Additionally, the microparticles have been shown to prolong the biocidal effect of the fungicide under accelerated weathering tests by protecting the biocide from UV-induced chemical degradation.     

Experimental and modeling analysis of diffusive release from single‐shell microcapsules

There is much experimental and mathematical work that describes chemical transport from multilayered films of planar geometries. There is less so, however, for chemical transport from multilayered spheres, a common structure for controlled‐release materials. Based on the Sturm–Liouville approach of Ramkrishna and Amundson (1974), explicit analytical solutions for the concentration profiles and release kinetics from spherical capsules are presented. Fluorescent dye‐release studies using single‐shelled microspheres called nanoparticle‐assembled capsules were performed to validate the model for uniformly and nonuniformly sized capsules. The combined experiment‐modeling approach allows optical microscopy images and release measurements to be readily analyzed for estimating diffusion coefficients in capsule core and shell walls. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Insect sex pheromones: Evaporation rates of alcohols and acetates from natural rubber septa

The half-lives (t _1/2) of alcohol sex pheromones, 1-alkanols, acetate sex pheromones, and an epoxide (disparlure) were determined on natural rubber septa. Thet _1/2 values for the homologous alcohols from decanol to heptadecanol increased regularly from 2.2 to 1117 days, but thet _1/2 of octadecanol was 609 days. Thet _1/2 values of (Z)7-, (E)7-, and (Z)9-tetradecen-1-ol acetates were 154, 168, and 199 days, respectively, whereas those of five other tested 14-carbon acetates ranged from 310 to 350 days. The dependence oft _1/2 values on chain length and double-bond position is consistent with the hypothesis that molecular size is an important variable affectingt _1/2 values. Also, in accordance with the hypothesis, when aZ-alkenyl compound has a much shortert _1/2 than the corresponding saturated compound, thet _1/2 values of theZ compound and itsE isomer may be quite different. Thus, (E)-9-tetradecen-l-ol acetate had at _1/2 of 331 days. Thet _1/2 of disparlure was 180 days. The effect of thecis-7,8 epoxide group is apparently similar to that of the olefin group in lowering thet _1/2 below the value that would be expected solely on the basis of chain length.This paper reports the results of research only. Mention of a commercial product in this paper does not constitute a recommendation by the U.S. Department of Agriculture.     

Application of hot-melt coating for controlled release of propranolol hydrochloride pellets

Waxes are available in various lyophilicity, and they can be used to regulate the release from multiunit-controlled release pellets. In this study, the application of saturated polyglycolysed glyceride (Gelucire® 50/02) and glycerol palmitostearate (Precirol® ATO5) as drug release regulators for propranolol pellets and the kinetics of release were investigated. Propranolol pellets containing 60% microcrystalline cellulose (Avicel® PH101) were prepared by using direct pelletization technique in a fluidized-bed rotary granulator (Glatt GPCG1). The pellets of 16:18 mesh size were collected and coated with the molten wax(es) at various ratios and thicknesses in a fluidized-bed top spray coater (Glatt GPCG1). The dissolution was determined using test method for Propranolol Extended Release Capsules USP 24 and was found to be very rapid with the uncoated pellets. The dissolution of coated pellet was decreased with the increases in Precirol ATO5 proportion and coating thickness. Plot of log % drug release vs. reciprocal of time showed a good linear relationship. The k value derived from the slope of the plot and designated as a “diffusive resistance constant” linearly increased with the coating level. The findings indicated that drug release could be adjusted by varying the ratio of Precirol® ATO5 to Gelucire® 50/02 as well as the thickness of the coat.     

Preparation and characterization of polyurethane based on dimer acid for environment-friendly controlled release fertilizers

ABSTRACT

The paper presents a new controlled release fertilizer coated by dimer acid-based polyurethane (PU). The structure and property of the sample were characterized. Results indicated that the polyether polyol modified PU (MPU) coating reduced water absorption rate by 72.1% after 29 d, and increased the cross-linking density by 23%, and decreased the coating porosity by 26%, Moreover, MPUFs and PUFs both exhibited excellent nutrient controlled release abilities, especially the MPUF possessed longer nitrogen release longevity (118 d,131%) compared with PUF (51 d). Thus, the high-performance MPUFs with environmentally friendly and excellent controlled release could be widely applied to agricultural fields.     

Dendronized polymer as building block for layer-by-layer assembly: Polyelectrolyte multilayer films for incorporation and controlled release of water-insoluble dye

The multilayer films of the carboxylic acid terminated Fréchet-type dendronized polymer (denpol) and poly(diallyl-dimethylammonium chloride) (PDDA) were fabricated using the electrostatic layer-by-layer (LbL) assembly technique on planar substrates. The influence of pH and ionic strength of the polyelectrolyte dipping solutions on the fabrication of the PDDA/denpol multilayer films has been investigated in detail. AFM images showed that pH of the polyeletrolyte dipping solutions can obviously influence the surface morphology and roughness of the denpol layer in the multilayer films. We also use a preassembly method for incorporating water-insoluble molecule of pyrene into interior of denpol, and then fabricate the PDDA/pyrene-loaded denpol multilayer films. Moreover, we demonstrated that the loaded pyrenes can be released from the LbL films, which can be controlled by ionic strength of immersing solutions. Interestingly, the pyrene-released multilayer film can be used to reload pyrene when immersing the pyrene-released film into a saturated aqueous solution of pyrene.     

A polypyrrole-based microchip for controlled drug release

A novel polypyrrole-based microchip has been developed by electrochemical deposition of drug-doped polypyrrole films on the Au microelectrode arrays. The drug release from the microchip is controlled by a potential application. Due to its unique configuration, the microchip exhibits some appealing characteristics, such as being able to supply single or multiple drugs with precise small doses, ability to achieve pulsatile release mode, small in size, and good biocompatibility, and thus has the potential for application as implantable device in the field of controlled drug release.     

Antifouling effect of hydrogen peroxide release from enzymatic marine coatings: Exposure testing under equatorial and Mediterranean conditions

Hydrogen peroxide (H₂O₂) may be considered an environmentally friendly antifouling alternative to common biocides such as Cu₂O and various organic compounds. In this work, the efficiency of antifouling coatings releasing hydrogen peroxide via enzyme-mediated conversion of starch, under Mediterranean and equatorial climatic conditions, is investigated. During seawater exposure of the coatings, starch is first converted to glucose by glucoamylase (rate-controlling step) and subsequently glucose is rapidly oxidised by hexose oxidase in a reaction producing hydrogen peroxide.