Grinding aids are surface active substances, wich separate particles of milled substance and prevent their reaglomeration.

Concern within the public health community is mounting regarding what some deem as "candy-flavored tobacco". A recent study by King et al. (2014) found that >40% of middle and high school student smokers use flavored cigarettes or flavored little cigars. This study investigated the validity of the "candy-flavored tobacco" designation by comparing flavor profiles of 18 flavored tobacco products with 15 candy and Kool-Aid products using gas chromatography mass spectrometry (GC/MS). Significant compositional overlap was found; nearly 75% of the compounds detected were present in at least one flavored tobacco and one candy or Kool-Aid product. Benzaldehyde and or benzyl alcohol were measured in cherry candies, Kool-Aid and tobacco. Similar levels of benzaldehyde were measured in the cherry Kool-Aid and wild cherry Cheyenne cigars at 3338 ± 623 and 3937 ± 251 μg/serving. Methyl anthranilate, 1-hexanol, [lowercase gamma]-decalactone, and raspberry ketone were found in all grape, apple, peach and berry products, respectively. Vanillin and or ethyl vanillin were constituents of all flavored tobacco products analyzed. Many flavorants, such as limonene, are also volatilizable biogenic organic compounds (VBOCs). A more comprehensive understanding of the identities and properties of VBOCs, precursors to secondary organic aerosol (SOA), would support air quality and climate change research and management. Our knowledge is limited by extreme compositional diversity within the VBOC class. Only recently have techniques such as two-dimensional gas chromatography time of flight mass spectrometry (GCxGC/TOFMS) been employed, and the complexity of the data poses analysis challenges. To address this, agglomerative hierarchical cluster analysis (HCA) was performed on data generated by GCxGC/TOFMS analysis of air samples collected during the Particle Investigations at a Northern Ozarks Tower: NOx, Oxidant, Isoprene Research (PINOT NOIR) study. HCA resulted in the assignment of 204 compounds into 27 clusters: these clusters were grouped into 4 distinct types making the data significantly more manageable. The assignment of a cluster to a type was mostly based on the frequency with which compounds appeared in samples. Type I clusters contained compounds that were present in only one sample, suggesting meteorological influence.

No description available.

No description available.

No / There is considerable interest, both fundamental and technological, in understanding how additives and impurities influence crystal nucleation, and in the modulation of nucleation in a predictable way by using designer additives. An appropriate additive can promote, retard, or inhibit crystal nucleation and growth, assist in the selective crystallization of a particular enantiomer or polymorphic form, or enable crystals of a desired habit to be obtained.[1¿3] Applications involving additives include the control of the nucleation of proteins,[4] the inhibition of urinary-stone formation[5] and of ice formation in living tissues during cryoprotection,[6] their use as antifreeze agents in Antarctic fish,[7,8] the prevention of blockages in oil and gas pipelines as a result of wax precipitation[9] and gas-hydrate formation,[10] crystal-twin formation,[11] and as a possible basis for the antimalarial activity of some drugs.[12]We report herein the mode of action and explicit (apparently intuitive) rules for designing additive molecules for the modulation of crystal nucleation. The mode of action and the design features have been derived from molecular-dynamics simulations involving simple models.[13] These findings will help to rationalize how known nucleation inhibitors and modulators exert their effect and aid in the identification or design of new additives for the inhibition or promotion of nucleation in specific systems.

Call number: LD2668 .T4 1979 P6 / Master of Science

Call number: LD2668 .T4 1979 T52 / Master of Science

LD2668 .T4 1962 P57

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This work involves the study of the effects of Reversible Addition-Fragmentation Chain Transfer (RAFT) agents on the emulsion polymerization of styrene. The feasibility of RAFT as a method for obtaining controlled radical polymerizations in emulsion systems is also investigated. Both seeded and ab initio systems were studied with three RAFT agents of varying structure. Inhibition and retardation effects on addition of various amounts of the RAFT agents to the emulsion systems were observed and the trends noticed. The effect of the RAFT agents on the average number of radicals per latex particle was calculated from reaction rates. The effect of the RAFT agent on the molecular weight and the molecular weight distribution was monitored by gel permeation chromatography. Exit of free radicals from the latex particles proves to be a major feature in the studied RAFT emulsion systems. Fragmentation of the RAFT agent in the latex particles, gives rise to free radical species that can exit from the particle and enter other particles where they can either terminate instantaneously or propagate. The exit and termination processes presumably result in both the inhibition and retardation of the emulsion polymerizations. A linear increase in Mn with conversion is observed, however the low concentration of RAFT agent in the latex particles is responsible for the obtained number average molecular weights being much higher than predicted. The low concentrations of RAFT agents in the latex particles is also responsible for the broad molecular weight distributions that are obtained. Reaction conditions for RAFT experiments should to be chosen so that the effects of exit processes are minimized and that the RAFT agent is primarily situated in the latex particles. These conditions must be met if the RAFT process is to be successful as a method of controlled radical polymerization in emulsions. / AFRIKAANSE OPSOMMING: Hierdie navorsing behels die studie van die effek van In bygevoegde addisie-fragmentasie kettingsoordragsreagent (RAFT1) op die emulsie polimerisasie van stireen. Die uitvoerbaarheid van RAFT as 'n metode om gekontroleerde radikale polimerisasies in emulsiesisteme te verkry is ook ondersoek. Eksperimente met drie RAFTkettingoordragsreagente van gevarieerde strukture is uitgevoer in beide seeded en ab initia sisteme. Die effek van die RAFT-reagent op die inhibisie en vertraging van die emulsie polimerisasie is waargeneem en die invloed van RAFT op die gemiddelde aantal radikale per partikel is bepaal. Die ontwikkeling van die molekulêre massa en die molekulêre massadistribusie is waargeneem deur middel van gel permeasie- kromatografiese tegnieke. Die ontsnapping van vrye radikale vanuit die partikels was 'n belangrike faktor in RAFT emulsiesisteme wat ondersoek is. Hierdie radikale is gegenereer deur die fragmentasie van die oorspronklike RAFT-reagent. Fragmentasie van die RAFT-reagent in die lateks partikels lei tot die vorming van vrye radikale spesies wat uit een partikel kan ontsnap en ander partikels kan binnedring waar dit onmiddellik kan termineer of propageer. Die ontsnappings- en terminasieprosesse van vrye radikale lei oënskynlik tot die inhibering en vertraging van die emulsie polimerisasie. 'n Lineêre verhoging in die gemiddelde molekulêre massa tydens konversie is waargeneem, alhoewel die Mn-waardes baie hoër was as wat verwag is. Die verskil kan toegeskryf word aan die klein hoeveelhede van die RAFT-reagent wat in die partikels teenwoordig is. Hierdie lae RAFT-konsentrasies is ook verantwoordelik vir die breë molekulêre massa distribusie wat waargeneem is. Vir die RAFT-proses om suksesvol te wees in gekontroleerde radikale polimerisasies in emulsies, moet reaksie kondisies so gekies word dat die ontsnapping van vrye radikale tot 'n minimum beperk word en die RAFT-reagent hoofsaaklik in die lateks partikels teenwoordig is.

Daugumos hidrotechnikos statinių ir jų konstrukcijų statyboje pagrindinė naudojama medžiaga yra betonas ir gelžbetonis. Kadangi šie statiniai pastoviai sąveikauja su agresyvia aplinka (vandens lygių svyravimas, vandens slėgis, šaltis, saulės radiacija, vėjas, ledas) jie turi ypatingai pasižymėti patvarumu ir ilgaamžiškumu. Todėl šios konstrukcijos privalo būti atsparios minėtiems veiksniams. Betonui kietėjant atsiranda nepageidaujamas reiškinys - betono susitraukimas. Dėl susitraukimo betone atsiranda mikroplyšiai ir įtrūkimai, o betonas tampa mažiau atsaparus minėtų veiksnių poveikiui. Todėl šiame darbe buvo atliekami bandymai su betono susitraukimą mažinančiais priedais, norint įšsiaiškinti kokią įtaką jie turi įvairioms betono savybėms. Šios medžiagos pagerina betono savybes, tai yra sumažina susitraukimą, vandens įgeriamumą, padidina atsparumą lenkimui ir gniuždymui, o tai suteikia konstrukcijoms patvarumą ir ilgaamžiškumą. Tyrimų metu buvo nustatinėjama susitraukimą mažinančių priedų įtaką betono mišinio tankiui, betono mišinio konsistencijai, betono susitraukimui, betono stipriui lenkiant, betono stipriui gniuždant, betono vandens įgeriamumui. Bandymų metu gautų rezultatų pagindu nustatyti efektyviausiai veikiantys priedai. / Concrete and reinforced concrete are the main materials used for most hydraulic constructions and its structures building. Since these constructions constantly interact with aggressive environment (water levels fluctuation, water pressure, cold, sun radiation, wind, ice), it have to be durable and long-term. Therefore these constructions have to be resistant to mentioned factors. When concrete is hardening, often unwelcome phenomenon appears – concrete shrinkage. Due to the shrinkage of the concrete occurs the microcracks and the crack, and the concrete becomes less resistant for aggressive environment. So in this final work there were done many tests with concrete shrinkage redusing additives mix, in order to find out what influence they have to variuos concrete features. These materials improve concrete features, it means reduce shrinkage, water absorption, increase resistance to bending and compression. This gives stability and long-term to constructions. During the research it was determined shrinkage redusing additions influence to concrete mixture density, consistency, concrete shrinkage, bending strength, compressive strength, water absorption. During the research results effectively acting additions were determined.