Crosslinking kinetics in emulsion polymerization

Network formation in free-radical polymerization is investigated both from experimental and theoretical points of view. In a bulk free-radical crosslinking copolymerization, the radical concentration increases significantly due to a decrease in the bimolecular termination rate. Some fraction of radicals is trapped during the course of network formation, and the reactivity of the radicals in liquid state is completely different from that in solid state (trapped radicals) in terms of both propagation and termination. In emulsion crosslinking polymerization, the crosslinking density tends to be fairly high even from the start of the polymerization. The crosslinking density development is substantially different from that in bulk and solution polymerizations, in which the crosslinking density increases with time, at least in the earlier stages of polymerization. Due to the elastic contribution of free energy change, the monomer concentration in the polymer particles is lower than for linear emulsion polymerizations as long as the monomer droplets exist, resulting in an enhanced tendency toward crosslinking reactions.     

The role of aqueous-phase kinetics in emulsion polymerizations

The kinetics of species in the aqueous phase control many events in emulsion polymerization: the rate of entry of free radicals into particles (equivalent to initiator efficiency), the rate of exit (desorption) of free radicals from particles, the fate of desorbed free radicals and of free-radical species derived directly from aqueous-phase initiator. Aqueous-phase kinetics also dominate particle nucleation and re-seeding (secondary nucleation), and the in situ formation of surfactant. The mechanisms of each of these events are discussed, and it is shown how general methods can be constructed to deduce the ratedetermining events for each of these. The methodology is then applied extensively to styrene, which leads to the following conclusions. (a) The aqueous-phase events which govern entry (initiator efficiency) are propagation and termination, with entry occurring irreversibly when a critical degree of propagation z is reached so that the resulting species (a di- or tri-styrenesulfonate species in the case of styrene with persulfate initiator) is sufficiently surface-active that, once adsorbed onto the particle it does not desorb before it propagates; the actual adsorption event is sufficiently rapid so as not to be rate-determining except during nucleation. (b) Exit of free radicals is governed by transfer inside the particle to form a monomeric radical which may desorb and diffuse irreversibly away from the parent particle before it propagates therein. (c) The fate of desorbed free radicals in the wide range of styrene systems examined is to re-enter another particle and remain therein, rather than the other possible fates (aqueous-phase termination or re-exit until intra-particle termination eventually occurs). (d) Below the cmc, nucleation is by the homogeneous-coagulative mechanism, while above the cmc, nucleation is through a process which combines the essential features of both homogeneous-coagulative and micellar-entry models. (e) Analysis of the aqueous-phase products produced in an emulsion polymerization shows that the species involved in termination, entry and exit also undergo subsequent reactions: hydrolysis and reaction with persulfate.     

Reaction kinetics of vinyl acetate emulsion polymerization

Transport of free radicals out of latex particles into the aqueous phase plays an important role in the emulsion polymerization of vinyl acetate. This so-called “desorption” process involves chain transfer to monomer which generates a mobile and rather stable monomer-unit free radical followed by the diffusion of this free radical out of the latex particle. A kinetic model is developed based on the reaction mechanisms of such an emulsion system. The experimental data available in the literature are used to test the model under various polymerization conditions. Reasonable agreement between the model predictions and experimental data is observed.     

Synthesis and kinetics of microgel in inverse emulsion polymerization of acrylamide

The kinetic behavior is studied in inverse emulsion polymerization of acrylamide. The polymerization rate in a micelle is proportional to the monomer concentration and the effective average radical concentration. When concentrations of monomer and radical are too low to proceed the polymerization only, some finite final conversion is obtained. The micelles of various sizes have different effective average radical concentrations at the same monomer concentration. Therefore, the polymerization rate and the final conversion are different for various sized micelles. The minimum amounts of emulsifier required to get stable state during reaction is 10 and 7 wt% (based on oil phase) in toluene and n-heptane systems, respectively. Phase inversion is observed with the increase of viscosity during polymerization. The final latex coagulates obviously in the toluene system even with 10 wt% of emulsifier, however, it can be improved more in the n-heptane system with 10 wt% of emulsifier. The crosslinking agent which copolymerizes with the monomer was supposed to remain in the interface of micelles. Such interfacial copolymerization not only hardens particles but improves the stability of the system also, therefore avoiding coagulation among particles. An increase in the content of crosslinking agent leads to a more uniform size of final particles. The microgel added in the alkyd resin decreases the drying time. The greater the amount of microgel added, the shorter the drying time.     

Erythrocytes carotenoids after astaxanthin supplementation in middle-aged and senior Japanese subjects

A randomized, double-blind human trial was conducted to assess the effect of 4- or 12-week astaxanthin supplementation (1 or 3 mg/day) on the carotenoid compositions of erythrocytes in Japanese middle-aged and senior subjects. Erythrocyte astaxanthin concentrations after 4- or 12-weeks of supplementation (3 mg/day) was significantly higher than after placebo or 1 mg astaxanthin supplementations. No differences were observed in either the carotenoid compositions or the phospholipid hydroperoxide concentrations in erythrocytes after astaxanthin intake in both the 1 and 3 mg/day groups.     

Suspension,bulk, and emulsion polymerization of vinyl chloride—mechanism,kinetics, and reactor modelling

A review of relevant microscopic processes, both chemical and physical, which occur during suspension, bulk and emulsion polymerization (both before and after pressure drop) is given. The state of the art of kinetic modelling of monomer consumption rate, reactor pressure, molecular weight and short and long chain branching development and polymer chain microstructure is illustrated. The effects of diffusion-controlled termination and propagation reactions and the significant decrease in initiator efficiency and decomposition rate constant at high monomer conversions on the relative rates of various chemical reactions are discussed. The application of temperature programming and semibatch operation are emphasized. Finally, attempts to model polymer particle morphology are described.     

非等温DSC法研究VAc-BA-AM共聚乳液固化反应动力学

以醋酸乙烯酯、丙烯酸丁酯、丙烯酰胺为单体,通过半连续乳液聚合方法制备PVC皮革用胶黏剂,借助非等温DSC法(差示扫描量热法)研究共聚乳液的固化过程。使用Kissinger方程、Crane方程和T-β(温度-升温速率)外推法,计算共聚乳液体系固化反应的动力学参数和固化温度。结果表明,共聚乳液体系固化反应的表观活化能为51.71 k J/mol,指前因子为2.79×106S^(-1),反应级数为0.889,最佳固化温度为295.4 K。     

非等温DSC法研究VAc-BA-AM共聚乳液固化反应动力学

以醋酸乙烯酯、丙烯酸丁酯、丙烯酰胺为单体,通过半连续乳液聚合方法制备PVC皮革用胶黏剂,借助非等温DSC法(差示扫描量热法)研究共聚乳液的固化过程。使用Kissinger方程、Crane方程和T-β(温度-升温速率)外推法,计算共聚乳液体系固化反应的动力学参数和固化温度。结果表明,共聚乳液体系固化反应的表观活化能为51.71 k J/mol,指前因子为2.79×106S~(-1),反应级数为0.889,最佳固化温度为295.4 K。     

乳胶基质老化过程的结晶动力学研究

乳胶基质作为乳化炸药的主体材料,其储存过程中的老化程度关系着产品的使用性能。通过分析乳胶基质的老化机理,从结晶动力学角度对其老化规律进行研究,得到了乳胶基质的老化方程。采用实验数据对老化方程进行验证,结果表明该方程具有很好的拟合优度。老化方程中的特征时间表征了在某种外界环境下,乳胶基质老化速率达到最大值时所需要的时间,是对乳胶基质稳定性的一种量化,有助于评判相似老化条件下,不同产品的储存性能。     

Phase separation kinetics of maya asphaltene emulsion and free-to-bound water transformation

Differential scanning calorimetry (DSC) and inelastic neutron scattering were applied to study the phase separation kinetics of Maya asphaltene water-in-oil emulsion by following the water separation from the upper phase. In addition, transformation of the separated water from the free state to the bound and/or restricted state was also investigated. Maya asphaltene in toluene with 0.1 M HCl forms emulsion following ultrasonic or high speed mechanical emulsification. Initially, water molecules in the emulsion are largely free water. The emulsion gradually separates into two phases and at the 7th day over 90% of water molecules have situated at the bottom phase. In the mean time water molecules at the free state initially slowly transform into bound state in a much slower pace (over 100 days) than the phase separation kinetics.     

Effects of inorganic electrolytes upon emulsion polymerisation reactions. I. Effects upon kinetics of styrene emulsion homopolymerisation and of styrene-acrylic acid emulsion copolymerisation

Results are given for the effects of two added inorganic electrolytes, potassium chloride and calcium chloride, upon the kinetics of the emulsion homopolymerisation of styrene and of the emulsion copolymerisation of styrene with a minor amount of acrylic acid, using sodium dodecylbenzenesulphonate as surfactant and potassium persulphate as initiator. Three reaction systems were investigated. Two were for the emulsion homopolymerisation of styrene, one reaction system using a relatively high level of surfactant and the other a relatively low level of surfactant. The third reaction system was for the emulsion copolymerisation of styrene and acrylic acid using an intermediate level of surfactant. The results show that the effects of added electrolytes can be varied and complex: they depend upon several factors such as the nature and amount of the added electrolyte, the level of surfactant, and the presence or absence of the acidic comonomer.     

Impact of rye-based evening meals on cognitive functions,mood and cardiometabolic risk factors: a randomized controlled study in healthy middle-aged subjects

Background

Whole grain (WG) intake is associated with reduced risk of obesity, type 2 diabetes and cardiovascular disease, whereas type 2 diabetes increases the risk of cognitive decline and dementia. The purpose of this study was to investigate the effects of short-term intervention with WG rye on cognitive functions, mood and cardiometabolic risk markers in middle-aged test subjects.

Method

Rye-based breads were provided to 38 healthy test subjects (aged 52-70y) during three consecutive days in a crossover study design, using white wheat flour bread (WWB) as a reference. The rye-based bread consisted of a WG rye kernel/flour mixture (1:1 ratio) supplemented with resistant starch type 2 (RS2) (RB?+?RS2). The last bread portion was ingested at 2100 h, and cognitive function, mood and cardiometabolic risk markers were determined the following morning, 11???14 h post intake.

Results

In comparison to WWB, the RB?+?RS2 product increased ratings of mood parameters (valance, P?<?0.001; activation P?<?0.05). No differences were seen in the cognitive tests depending on intervention (P?>?0.05). RB?+?RS2 increased insulin sensitivity (P?<?0.05), fasting levels of gut hormones (PYY, P?<?0.05; GLP-2, P?<?0.01) and fasting concentrations of plasma acetate, butyrate and total SCFA (P?<?0.001). In contrast, fasting levels of IL???1β were decreased (P?<?0.05). Insulin sensitivity was positively correlated with working memory test performance (P?<?0.05).

Conclusions

This study display novel findings regarding effects of WG rye products on mood, and glucose and appetite regulation in middle-aged subjects, indicating anti-diabetic properties of WG rye. The beneficial effects are suggested to be mediated through gut fermentation of dietary fiber in the RB?+?RS2 product.

Trial registration

The study was retrospectively registered at ClinicalTrials.gov, register number NCT03275948. Registered September 8 2017.

     

Effect of impurities on emulsion polymerization: Case II kinetics

The effects of water-soluble and monomer-soluble impurities on the kinetics of emulsion polymerization of monomers following Case II kinetics (e.g., styrene) are investigated. Experimental studies reveal that impurities can have an appreciable effect on both polymer particle nucleation and growth. These effects are shown to be well predicted by a mathematical model.     

Effect of impurities on emulsion polymerization: Case I kinetics

The effect of water- and monomer-soluble impurities on the kinetics of emulsion polymerization for Case I systems (e.g., vinyl acetate and vinyl choride) was investigated. Model predictions on the effect of these impurities on polymer particle nucleation and growth rate are shown to be in satisfactory agreement with experimental results. The effect of monomer-soluble impurities is shown to be quite different from that observed in Case II emulsion polymerization systems.     

DSC measurements and modelling of the kinetics of methane hydrate formation in water-in-oil emulsion

The kinetics of formation of clathrate hydrates of methane was investigated in a water-in-oil emulsion using high-pressure differential scanning calorimetry in the range 10-40 MPa, at various temperatures. At high driving force, the heat peak related to the formation of hydrates has a regular and symmetric shape, and its height and width depend on the gas pressure and sub cooling degree. At near equilibrium conditions, hydrate formation is delayed by more than 1 h, but is still clearly observable. A model based on crystal growth theory, coupled with a normal distribution of induction times to take into account the germination in a population of micro-sized droplets, is proposed to represent the hydrate formation rate versus time in the particular case of water-in-oil emulsions. It uses four parameters which appear strongly correlated to the experimental conditions: the growth rate constant, the over saturation of gas in the water phase, the average and standard deviation of the induction time distribution.     

Morphological characterization and kinetics study of polyaniline film formation by emulsion polymerization

The kinetics and morphology of polyaniline film prepared by using ammonium persulfate (APS) as oxidant and dodecylbenzoyl sulfonic acid (DBSA) as both emulsifier and dopant were studied in this paper. The kinetics of the formation of polyaniline film was determined by using the quartz crystal microbalance (QCM), and the film morphology was characterized by scanning electron microscopy (SEM). The reaction exhibited half-order kinetics with respect to APS concentration and first-order kinetics with respect to aniline concentration. The activation energy is 41.15 kJ/mol, and the growth rate of PANI film increased with increasing temperature and decreased with increasing concentration of DBSA.     

The kinetics of methyl linoleate emulsion autoxidation in the presence of polyhydroxy compounds

The kinetics of the autoxidation of methyl linoleate emulsions activated by carbohydrates likely to be present in meat, with special reference to the effects of functional groups, number of carbon atoms and configuration have been investigated by the rate of oxygen uptake. On the basis of equimolar concentrations of aldoses in the system, oxidation rate of methyl linoleate increases as the number of carbon atoms in the sugar molecule decreases, reaching a maximum in the presence of glyceraldehyde. Configuration of the aldose has a slight effect on the oxidation rate of methyl linoleate emulsions. At comparable molar ratios of hexose to methyl linoleate, the rate of oxidation was found to be: ketohexose > aldohexose > hexahydroxy alcohol. Replacement of the primary alcohol group in an aldohexose with a methyl group decreases the oxidation rate of methyl linoleate emulsion. An opposite effect is observed when the primary alcohol group is substituted with a carboxyl group, i.e., in the presence of sodium glucuronate. 2-Deoxy-D-glucose and 2-deoxy-D-ribose exhibit a lesser effect on the autoxidation of methyl linoleate emulsion than glucose and ribose, respectively. Oxidation rates in the presence of reducing disaccharides, maltose, lactose and cellobiose, are more rapid than in the presence of the non-reducing disaccharide sucrose. Presented at the AOCS Meeting, Toronto, 1962. American Meat Institute Foundation Journal Paper No. 254.     

Increases in hyperlipoproteinemia,disturbances in cholesterol metabolism and atherosclerosis induced by dietary restriction in rabbits fed a cholesterol-rich diet

The influence of dietary restriction on cholesterol transport and metabolism was investigated in rabbits given standard or cholesterol-rich diets (0.2 g cholesterol/kg body weight daily) eitherad libitum or with 50% caloric ration. Dietary restriction which has only a slight influence in control rabbits markedly aggravated the disturbances induced by exogenous cholesterol. With limited feeding, control rabbits presented a moderate increase in plasma cholesterol, whereas marked aggravation of hypercholesterolemia was observed in cholesterol-fed rabbits. Analysis of the lipoprotein profile showed that the excess of plasma cholesterol with the restricted cholesterol-rich diet corresponded to an increase in the concentration of very low density lipoprotein (VLDL) and low density lipoproteins (LDL) without any additional changes in the composition of these lipoproteins. No significant change appeared in the high density lipoprotein (HDL) concentration. The parameters of cholesterol metabolism were determined, from the curves of [³H] cholesterol radioactivity decrease, using a two-pool model. The increase in cholesterol turnover rate induced by the cholesterol-rich diet was accentuated by dietary restriction, whereas rabbits on standard restricted diet showed a slight decrease. The large increase in the size of both pools A and B in cholesterol-fed rabbits was even more pronounced with limited feeding. Dietary restriction induced additional accumulation of cholesterol in the aortic wall and the grade of the lesions was also aggravated.     

Seeded emulsion polymerization of vinyl chloride. A new approach to mechanism and kinetics

Some peculiarities concerning the mechanism and the kinetic behaviour of the vinyl chloride emulsion polymerization are described. Seeded emulsion polymerizations in the presence of an adequate mixture of anionic and non-ionic surfactants were carried out in order to avoid the micellar initiation. New kinetic parameters were determined from the experimental data as follows: (i) MSA, the minimum surface area of polymer seed particles necessary to capture all ion-oligoradicals generated in aqueous phase at a given initiator concentration; (ii) MCCI, the maximum critical concentration of initiator per unit surface of polymer particle under which the formation of new polymer particles is avoided; (iii) PVR₁, the polymer volume per active growing radical, necessary to be within the particle for 1 s. It was found that the average number of propagating radicals per particle, n, depends on the size of the polymer particle, as a resultant of entry and exit and then of the initiation and termination reactions. The practical consequences of the accurate control of the polymer particles growing during seeded emulsion polymerization of vinyl chloride were emphasized.     

Fast re-oxidation kinetics and conduction pathway in Spark Plasma Sintered ferroelectric ceramics

The re-oxidation kinetics of BaTiO₃ ceramics sintered by Spark Plasma Sintering (SPS) was investigated using in-situ impedance spectroscopy. Thanks to the flexibility of the SPS process, the grain size of the dense ceramics was tuned from 0.5 μm to 10 μm. The re-oxidation kinetics are found to be very fast regardless of the grain size and a full re-oxidation of the ceramics are achieved after 20 h of exposure to an ambient environment at only 600 °C. The residual density of charge carriers is reduced when using finer starting powders. SPS ceramics made with micrometer size grains demonstrate a residual charge-carrier density that is one tenth that of ceramics made from 10 μm particles. Grain-boundary conduction is dominant through fine-grain SPS ceramics. This latter feature is similar to BaTiO₃ sintered using the conventional route with 10 μm size grain. Finally, the critical grain size for optimal dielectric permittivity is found to shift from 0.7 μm in standard ceramics to 1.5 μm in SPS ceramics.