Carbon dioxide is a clean and versatile solvent for the synthesis and processing of a range of materials. This review focuses on recent advances in polymer synthesis and processing using liquid and supercritical CO2. The synthetic techniques discussed include homogeneous solution polymerisation, precipitation polymerisation, dispersion and emulsion polymerisation, and bulk polycondensation. The formation of porous polymers and polymer blends is also considered, and the specific advantages of CO2 in these processes are evaluated in each case. The use of CO2 as a solvent for polymer processing is reviewed from a materials perspective, with particular attention being given to the formation of polymers with well defined morphologies. The variable solvent strength associated with supercritical fluids has been utilised in areas such as polymer fractionation and polymer extraction. Plasticisation phenomena have been exploited for the impregnation and heterogeneous chemical modification of polymeric materials. The formation of microcellular polymer foams by pressure induced phase separation is considered, as is the use of CO2 for polymer particle formation, spray coating, and microlithography. The aim of the review is to highlight the wide range of opportunities available to the materials chemist through the use of carbon dioxide as an alternative solvent.

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Polymer synthesis and processing using supercritical carbon dioxide

The barrier solutions presently available on the market all have their drawbacks, e.g. cost, water-sensitivity, opacity or perceived environmental bad-will. At the same time there is a trend to use more plastic-based packaging materials for different applications, e.g. as replacements for metal and glass containers. This situation has stimulated the industry to provide new, more efficient barrier solutions. The innovations go along five major lines: (a) thin, transparent vacuum-deposited coatings; (b) new barrier polymers as discrete layers; (c) blends of barrier polymers and standard polymers; (d) organic barrier coatings; and (e) nanocomposite materials. This paper provides a comprehensive review of the different approaches, outlining the principle behind each barrier technology, its performance, its potential and the companies developing and producing the materials. Copyright © 2003 John Wiley & Sons, Ltd.

Recent innovations in barrier technologies for plastic packaging—a review

Cellulose macro- and nanofibers have gained increasing attention due to the high strength and stiffness, biodegradability and renewability, and their production and application in development of composites. Application of cellulose nanofibers for the development of composites is a relatively new research area. Cellulose macro- and nanofibers can be used as reinforcement in composite materials because of enhanced mechanical, thermal, and biodegradation properties of composites. Cellulose fibers are hydrophilic in nature, so it becomes necessary to increase their surface roughness for the development of composites with enhanced properties. In the present paper, we have reviewed the surface modification of cellulose fibers by various methods. Processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed in this paper.

/pdf/cellulose-based-bio-and-nanocomposites-a-review-5484pyqycf.pdf

Cellulose-Based Bio- and Nanocomposites: A Review

Polyhydroxyalkanoates (PHAs) are gaining increasing attention in the biodegradable polymer market due to their promising properties such as high biodegradability in different environments, not just in composting plants, and pro- cessing versatility. Indeed among biopolymers, these biogenic polyesters represent a potential sustainable replacement for fossil fuel-based thermoplastics. Most commercially available PHAs are obtained with pure microbial cultures grown on renewable feedstocks (i.e. glucose) under sterile conditions but recent research studies focus on the use of wastes as growth media. PHA can be extracted from the bacteria cell and then formulated and processed by extrusion for production of rigid and flexible plastic suitable not just for the most assessed medical applications but also considered for applications includ- ing packaging, moulded goods, paper coatings, non-woven fabrics, adhesives, films and performance additives. The present paper reviews the different classes of PHAs, their main properties, processing aspects, commercially available ones, as well as limitations and related improvements being researched, with specific focus on potential applications of PHAs in packag- ing.

http://www.expresspolymlett.com/letolt.php?file=EPL-0005219&mi=cd

Polyhydroxyalkanoate (PHA): Review of synthesis, characteristics, processing and potential applications in packaging

The use of supercritical carbon dioxide as a processing solvent for the physical processing of polymeric materials is reviewed. Fundamental properties of CO2/polymer systems are discussed with an emphasis on available data and measurement techniques, the development of theory or models for a particular property, and an evaluation of the current state of understanding for that property. Applications such as impregnation, particle formation, foaming, blending, and injection molding are described in detail including practical operating information for selected topics. The review concludes with some forward-looking discussion on the future of CO2 in polymer processing.

A Review of CO2 Applications in the Processing of Polymers

Crystallization and thermal behaviour of poly (d(−) 3-hydroxybutyrate)/poly(epichlorohydrin) blends

Dyeing of Cotton in Supercritical Carbon Dioxide

We investigated the structure of silk fibroin dissolved in water and in water-organic solvent mixtures by CD and small-angle x-ray scattering (SAXS). CD spectra indicated a disordered secondary structure in water and a beta-sheet conformation in aqueous organic solvents, such as methanol, dioxane, and trifluoroethanol (in trifluoroethanol a transient form evolving toward beta-sheet conformation was seen just after dissolution). The SAXS technique indicated the presence of fibroin particles of lamellar shape. The molecular weight was 188,000 daltons in water and 302,000 daltons in aqueous methanol.

CD and small‐angle x‐ray scattering of silk fibroin in solution

Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant Kn are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account.

Alberto Seves

Papers

Crystallization and thermal behaviour of poly (d(−) 3-hydroxybutyrate)/poly(epichlorohydrin) blends

Dyeing of Cotton in Supercritical Carbon Dioxide

CD and small‐angle x‐ray scattering of silk fibroin in solution

Poly(ethylene oxide)/poly(ethyl methacrylate) blends: Crystallization, melting behavior, and miscibility

Small-angle X-ray scattering study of the phase structure of poly(d-(−)-3-hydroxybutyrate) and atactic poly(epichlorohydrin) blends