Dynamic Modelling of Emulsion Polymerization for the Continuous Production of Nitrile Rubber

Commodity and specialty-grade rubbers, such as styrene-butadiene (SBR) or nitrile-butadiene (NBR), are industrially produced in large trains of continuous reactors using an emulsion polymerization process. Both SBR and NBR systems are largely unstudied. Furthermore, the studies that have been published on NBR have been typically limited to issues concerning the characteristics of the product behaviour (i.e. oil/fuel resistance, tensile strength, hardness, compression set). In this work a detailed mathematical model has been developed in order to simulate the industrial production of NBR via emulsion copolymerization of acrylonitrile (AN) and butadiene (Bd) in batch, continuous and trains of continuous reactors. Model predictions include monomer conversion, polymerization rate, copolymer composition, number- and weight-average molecular weights, tri- and tetra-functional branching frequencies, and the number and average size of polymer latex particles. NBR is typically produced at low temperatures (5 to 10 degrees C) using a redox initiation system to generate free radicals. The system is typically composed of three phases, water, polymer particles, and monomer. Surfactants and electrolytes are used to stabilize the particle and monomer phases as polymerization proceeds. Of particular industrial importance, in today's world of tailor-made products, is detailed control over the polymerization reaction. Such control requires a deep understanding of the influence of various reactant feed rates and reactor operating conditions on the process response. In particular, policies to minimize copolymer composition drift and to control molecular weight, polydispersity and chain branching at desirable levels. The model is cast in a dynamic form using ordinary differential equations to describe the change of each species, the average number of particles, total average polymer volume, and the first three leading moments of the molecular weight distribution. With a multiphase system it is necessary to determine the concentration of each component in each phase. For this, a constant partition coefficient approach was adopted, as opposed to a purely thermodynamic approach. Particle generation was modelled considering both micellar and homogeneous mechanisms. Model parameters were obtained from the open literature or arrived at after sensitivity analysis. Simulations starting the reactors full of water, feeding all ingredients to the first reactor and using an average residence time of 60 minutes revealed considerable copolymer drift starting in the forth reactor (33% conversion), and heightened molecular weights and chain branching once the monomer phase disappeared (50% conversion). Further simulations revealed that both copolymer drift and the growth of molecular weight and branching could be controlled through additional feed streams of AN and chain transfer agent to downstream reactors. Furthermore, polymer productivity could be increased by appropriately splitting the total monomer feed between the first couple of reactors in the train

Versatile Routes for Acrylonitrile Butadiene Rubber Latex Hydrogenation

The direct catalytic hydrogenation of acrylonitrile-butadiene-rubber in latex form was studied for the development of a simple process for the modification of unsaturated diene-based polymers. Acrylonitrile-butadiene-rubber, known as NBR, is a rubber synthesized from acrylonitrile and butadiene (monomers) via copolymerization. It has been widely utilized as oil resistant rubber components in industry. Selective hydrogenation of the residual carbon-carbon double bonds (C=Cs) in the NBR backbone could improve its physical and chemical properties which greatly extend its range of application and lifetime. However, the current hydrogenation procedure involves a number of cumbersome steps which substantially increase the production cost. Hence, it is worthwhile developing new technology which HNBR could be synthesized in a cheaper and environmentally friendly way. Considerable efforts have been undertaken to realize this goal. Among them, hydrogenation of commercial NBR latex becomes especially attractive and promising. Direct hydrogenation of NBR in the latex not only avoids using large amounts of organic solvent which is required in polymer solution hydrogenation but also produces hydrogenated-NBR (HNBR) in the latex form which can be utilized for painting or coating. It has been reported that the commercial NBR latex could successfully be hydrogenated using RhCl(PPh3)3 with added triphenylphosphine (PPh3). High quality HNBR latex was obtained after the reaction. However, the hydrophobicity of RhCl(PPh3)3 and PPh3 greatly restrict their separation and diffusion in the NBR latex, resulting in a very low activity in the heterogeneous NBR latex system. In order to improve the process of NBR latex hydrogenation using the RhCl(PPh3)3/PPh3 catalytic system, an in-situ hydrogenation process was developed where RhCl(PPh3)3 was directly synthesized from the water-soluble catalyst precursor RhCl3 and PPh3 in the NBR latex. The catalyst precursor RhCl3 is soluble in the aqueous phase of the NBR latex and PPh3 was well dispersed in the aqueous NBR latex after adding small amounts of alcohol. Compared with using pre-made solid catalyst, the in-situ synthesized catalyst in the NBR latex could quickly be transported into the polymer particles and faster hydrogenation reaction was observed. In addition, the influence of various operational conditions on the hydrogenation rate; such as catalyst concentration, latex system composition, reaction temperature and hydrogen pressure have been studied. With the success of NBR latex hydrogenation using RhCl(PPh3)3 catalyst, two water-soluble analogs of RhCl(PPh3)3, RhCl(TPPMS)3 (TPPMS = Monosulfonated Triphenylphosphane) and RhCl(TPPTS)3, (TPPTS = Trisulfonated Triphenylphosphane) were then used for NBR latex hydrogenation. It was found that the difference of their solubility in water greatly affected their activities in NBR latex hydrogenation. Successful hydrogenation was achieved using the RhCl(TPPMS)3 catalyst while only low conversion was observed when using the RhCl(TPPTS)3 catalyst. The catalysts retention in the polymer is also in agreement with the reaction results. High conversion could only be achieved when the catalyst diffused into the polymer particles in the latex. Using the RhCl(TPPMS)3, the reaction could be carried out in a temperature range of 70°C to 120°C. And no co-catalyst ligand (i.e. TPPMS) was required for catalyst diffusion or reaction. In addition, the effects of the particle size of the NBR latex and the molecular weight of NBR (gel fraction) on hydrogenation were also investigated using lab made “in-house” NBR latices. It was found that the hydrogenation reaction was much faster with smaller particle size. It was also observed that the gel fraction in the latex particles greatly influenced the mobility of the polymer chains within the particles. In addition to the rhodium based catalysts, ruthenium based catalysts have also been investigated for NBR latex hydrogenation. With the recent findings of the hydrogenation activity of the Grubbs type metathesis catalyst, the hydrogenation of NBR latex was studied first using the second generation of Grubbs catalyst (G2). It was found using the G2 catalyst with small addition of organic solvent such as mono-chlorobenzene (MCB) to dissolve the catalyst resulted in a successful hydrogenation in NBR latex. Meanwhile, the metathesis activity of the G2 catalyst was also measured during the hydrogenation reaction. Comparing with conventional ruthenium catalysts, the multifunctional G2 catalyst benefited the NBR latex hydrogenation process by controlling its molecular weight change. The increase of molecular weight within hydrogenation reaction was partially offset by a synchronous metathesis reaction between NBR and the added of chain transfer agent (CTA). As a result, no visible gel was observed in the final HNBR product. In addition, the kinetic behavior of the hydrogenation was systematically studied with respect to the catalyst concentration, hydrogen pressure as well as NBR concentration. The apparent activation energy over the temperature range of 80-130°C for the hydrogenation of metathesized NBR was also measured. Further experiments showed that the second generation of Hoveyda-Grubbs catalyst (HG2) could be employed for the NBR latex hydrogenation even without adding any organic co-solvent to dissolve the catalyst. Although HG2 catalyst is insoluble in water, it could be well dispersed in aqueous system with the addition of certain surfactants. A fast catalytic hydrogenation (e.g. TOF > 7000 h-1 at 95 mol.% conversion) was achieved and successful hydrogenation was still observed under very low catalyst concentration. Compared with using G2 catalyst, the degree of metathesis reaction under HG2 in this organic solvent free process was very limited. As a result of this research project, different catalysts were successfully developed for hydrogenation of NBR in latex. A significant milestone was achieved in improving polymer hydrogenation technology.1 yea

Designing Ion-Containing Polymers with Controlled Structure and Dynamics

Ion-containing polymers are a unique class of materials for which strong electrostatic interactions dictate physical properties. By altering molecular parameters, such as the backbone chemical structure, the ion content, and the ion-pair identity, the structure and dynamics of these polymers can be altered. Further investigation of the molecular parameters that govern their structure-property relationships is critical for the future development of these polymeric materials. Particularly, the incorporation of ammonium-based counterions into these polymers offers a facile method to tune their electrostatic interactions and hydrophobicity. Applying this concept, a bulky dimethyloctylammonium (DMOA) counterion was used to modify the organic solubility of styrenesulfonate in order to facilitate its direct solution copolymerization with isoprene. With these poly(isoprene-ran-styrenesulfonate) (P(I-ran-SS)) copolymers the effect of ion content and the counterion identity on the structure and dynamics were evaluated. In the first project, poly(isoprene-ran-dimethyloctylammonium styrenesulfonate) (P(I-ran-DMOASS)) copolymers with high molecular weights and dimethyloctylammonium styrenesulfonate (DMOASS) compositions ranging between 8 and 40 mol% (30 - 77 wt%) were synthesized via nitroxide-mediated polymerization. Thermal and viscoelastic characterization revealed distinct behaviors for the low (30 - 51 wt%) and high (56 - 77 wt%) DMOASS content copolymers. Three structural regimes were identified: ion clusters (30 wt% DMOASS), continuous ionic phase (56 - 77 wt% DMOASS), and the coexistence of the two (42 - 51 wt% DMOASS). As DMOASS content increased, small angle X-ray scattering revealed a gradual transition from the characteristic ion cluster structure to a smaller, more regular backbone-backbone structure associated with a continuous ionic phase. The ion clusters acted as physical crosslinks and introduced additional elasticity into the low DMOASS content copolymer, while the continuous ionic phase showed restricted flow behavior and the disappearance of a definitive plateau modulus. Dynamic mechanical analysis revealed two distinct Tg’s at intermediate DMOASS content, indicating the coexistence of both structures. In the second project, the role of counterion sterics on the structure and dynamics of a low glass transition temperature, amorphous P(I-ran-SS) at low ion contents (7 mol%) was investigated using a series of symmetric, tetraalkylammonium counterions with methyl (TMA), ethyl (TEA), propyl (TPA), and butyl (TBA) pendent groups in addition to a sodium cation control. A detailed analysis of the aggregate structure was achieved by fitting the X-ray scattering profiles with a modified hard sphere model. Increasing the counterion sterics from sodium to TEA resulted in slight changes to the aggregates with some ionic groups present in the isoprene matrix. For the more sterically hindered TPA and TBA counterions, considerable disruption of the structure occurs. Using solid-state NMR, dynamic mechanical analysis, and rheology, the effect of the counterion sterics on the copolymer dynamics was determined. The larger counterions exhibited an increase in the dynamic moduli at high frequency while decreasing the dynamic moduli at lower frequencies in addition to possessing faster molecular dynamics. These two observations correspond to the incorporation of more ionic groups into the isoprene matrix and weakening of the dipole-dipole interactions, respectively. Lastly, binary mixtures of TMA and TBA ammonium counterions were employed in these P(I-ran-SS) copolymers. The P(I-ran-SS) ionomers with TMA:TBA weight ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 were prepared through solution blending. The SAXS profiles and Kinning-Thomas fitting showed only slight structural changes between 100:0 and 50:50, while major modification of the structure appears once the ratio reaches 75:25 and above. The alterations of the structure also indicated a mixed counterion aggregate structure. The linear viscoelastic characterization of the mixed counterion ionomers showed an increase in the polymer dynamics at low frequencies with increasing TBA weight percentages. Additionally, preliminary tensile tests were collected that showed increased mechanical properties with the stronger electrostatic interaction associated with TMA counterions. Thus, the structure and properties of these low Tg, amorphous ionomers can be specifically tuned by using multiple counterions. Through these studies, the role of both ion content and counterion identity on the structure and dynamics of low Tg, amorphous P(I-ran-SS) copolymers have been elucidated. Furthermore, ammonium-based cations have been shown to offer a versatile means to modify both the ion aggregate structure and interaction strength of an ionomer. Appropriate selection of the pendent groups and mixture of different counterions allow for the properties of the ionomer to be freely tuned

Planning of Petrochemical Industry under Environmental Risk and Safety Considerations

The petrochemical Industry is based upon the production of chemicals from petroleum and also deals with chemicals manufactured from the by products of petroleum refinery. At the preliminary stages of chemical plant development and design, the choice of chemical process route is the key design decision. In the past, economics were the most important criterion in choosing the chemical process route. Modified studies imply that the two of the important planning objectives for a petrochemical industry, environmental risk and the industrial safety involved in the development. For the economic evaluation of the industry, and for the proposed final chemicals products in the development, simple and clear economic indicators are needed to be able to indicate an overall economic gain in the development. Safety, as the second objective, is considered in this study as the risk of chemical plant accidents. Risk, when used as an objective function, has to have a simple quantitative form to be easily evaluated for a large number of possible plants in the petrochemical network. The simple quantitative form adopted is a safety index that enables the number of people affected by accidents resulting in chemical releases to be estimated. Environmental issues have now become important considerations due to the potential harmful impacts produced by chemical releases. In this study third objective of planning petrochemical industry was developed by involving environmental considerations and environmental risk index. Indiana Relative Chemical Hazard Score (IRCHS) was used to allow chemical industries routes to be ranked by environmental hazardous. The focus of this work is to perform early planning and decision-making for a petrochemical plants network for maximum economical gain, minimum risk to people from possible chemical accidents and minimum environmental risk. The three objectives, when combined with constraints describing the desired or the possible structure of the industry, will form an optimization model. For this study, the petrochemical planning model consists of a Mixed Integer Linear Programming (MILP) model to select the best routes from the basic feedstocks available in Kuwait -as a case study- to the desired final products with multiple objective functions. The economic, safety and environmental risk objectives usually have conflicting needs. The presence of several conflicting objectives is typical when planning. In many cases, where optimization techniques are utilized, the multiple objectives are simply aggregated into one single objective function. Optimization is then conducted to get one optimal result. This study, which is concerned with economic and risk objectives, leads to the identification of important factors that affecting the building-up of environmental management system for petrochemical industry. Moreover, the procedure of modelling and model solution can be used to simplify the decision-making for complex or large systems such as the petrochemical industry. It presents the use of simple multiple objective optimization tools within a petrochemical planning tool formulated as a mixed integer linear programming model. Such a tool is particularly useful when the decision-making task must be discussed and approved by officials who often have little experience with optimization theorie

Pressure sensitive adhesives from renewable resources

Pressure-sensitive adhesives (PSAs) represent an important segment of the adhesives market. In this work, novel insights into the adhesive performance of bio-based pressure sensitive adhesives are presented. Three different homopolymers based on fatty acids derived from native vegetable oils as renewable feedstock were characterized in terms of their mechanical and adhesive properties

Modeling and Simulation of Polymerization Processes

This reprint is a compilation of nine papers published in Processes, in a Special Issue on “Modeling and Simulation of Polymerization Processes”. It aimed to address both new findings on basic topics and the modeling of the emerging aspects of product design and polymerization processes. It provides a nice view of the state of the art with regard to the modeling and simulation of polymerization processes. The use of well-established methods (e.g., the method of moments) and relatively more recent modeling approaches (e.g., Monte Carlo stochastic modeling) to describe polymerization processes of long-standing interest in industry (e.g., rubber emulsion polymerization) to polymerization systems of more modern interest (e.g., RDRP and plastic pyrolysis processes) are comprehensively covered in the papers contained in this reprint

Application of surface thermal lens technology combined with polarization to the study of polymers

A new approach was attempted to investigate the characteristics of polymers by using photothermal technology. The Surface Thermal Lens (STL) technique was employed to study polymers because of its higher spatial resolution and greater sensitivity than the classical photothermal detection techniques (PDT). Zeonex [Cyclo-Olefin-Polymer] and acrylic [Poly–Methyl- Meth-Acrylate] were used as the samples. Polarization was applied to the STL technique. The signals of Zeonex were different from those of acrylic when the STL probe beam was polarized. Two different polarizer orientations for the probe beam, crossed and parallel, were used to observe the STL signal response to the samples. No time dependence in the STL signals of both Zeonex and acrylic was observed when the probe beam was unpolarized, but time dependence of the signals was observed when the probe beam was polarized. Zeonex showed the most significant signal changes under the crossed-polarizer conditions, and acrylic showed the most significant changes under the parallel-polarizer conditions, indicating a difference in the response of the chain-like molecules to the heating beam. Therefore, STL techniques using polarized light may provide new insight into structural changes in polymers

Anisotropic colloids in soft matter environments : particle synthesis and interaction with interfaces

We have shown new applications and synthetic routes for polymer colloids in the field of home and personal care products by controlling polymer and/or colloidal architectures. Our initial aim was to develop functional particles that imparted beneficial properties to fibrous substrates and as such our first goal was to develop a method for depositing particles onto such surfaces. Chapter 2 describes the method by which we achieved this goal, namely adding a small amount of a low glass transition polymer to an otherwise non-adhesive polymer to enhance colloidal deposition. Following on from this work we looked into ways in which to impart desirable characteristics from the particles onto fibres. In Chapter 3 we describe how the use of a hydrazide functional monomer in polymer gels can provide a continuing slow release of fragrance molecules that reacts to the environment it is held in such that if the local fragrance concentration is low then more is released. In Chapter 4 we describe the synthesis of highly porous particles with controlled pore sizes and the use of such particles in oil absorption for applications in water-free cleaning systems. The particles are capable of carrying many times their own weight in oil and are shown to be reusable. In Chapter 5 we describe a computational model that predicts the ability of a particle to stabilize emulsions. The model is highly adaptable and can be used to predict the surface activity of almost any particle morphology. Chapter 6 builds on this work and described the synthesis of highly anisotropic polymer particles by templating preexisting structures and explains their surface activity, or lack thereof

Development and evaluation of asphalt technologies utilizing renewable resources and innovative pavement systems

As the cost of construction materials continues to rise and place financial constraints on transportation agencies, engineers are looking for innovative technologies that minimize construction costs and optimize the selection of materials used in asphalt pavements. This dissertation includes a selection of four papers that advance the development, application, and utilization of innovative asphalt pavement technologies. Among the four papers, three subject areas in asphalt materials are examined to cultivate the use of newly-developed technologies in the asphalt industry. These include: the robust evaluation of hot mix asphalt from multi-state sources that utilize recycled asphalt shingles (RAS), the application and evaluation of a crack-relief interlayer asphalt mix design using new polymer technology, and the development of a bio-based thermoplastic elastomeric block-copolymer as a modifier for asphalt binder. In the case of the bio-based polymer, polymerized triglycerides from soybean oil serve as the rubbery block to replace butadiene in butadiene-based styrenic block co-polymers, thereby creating a new thermoplastic elastomeric polymer that is more renewable and biodegradable than its petroleum based counterparts. For each subject area, laboratory experiments were conducted on experimental asphalt materials to determine the performance characteristics for the development and/or evaluation of new technologies. The results of each study show the advantage of implementing the technologies in pavement applications. Asphalt formulations developed with the bio-based block-copolymer demonstrate the block-copolymer\u27s effectiveness in improving the rheological properties of asphalt binder; crack-relief interlayer mixes utilizing an improved polymer modified binder formulation are effective in delaying reflective cracking in overlay pavement systems; and a variety of asphalt pavements that incorporate RAS alone or in combination with other cost saving technologies can be successfully produced and meet laboratory performance testing standards