MATERIAL SCIENCE: THE EXTRACTION OF RAW MATERIALS                

FROM PLANTS               

The use of plants not only as food but also as flavouring, colouring or in medicine has a long history. The interest in aromatic and medicinal plants has declined over the last half century, mainly due to the tremendous developments in the production of synthetic substitutes. Nowadays however there is a resurgence of interest in natural remedies which is in part due to some disillusionment with modern medicines and the hope that new treatments can be resurrected from ancient remedies.

            Medicinal and aromatic plants provide an inexhaustible resource of raw materials for the pharmaceutical, cosmetic and food industries and more recently in agriculture for pest control. People have learned to increase the power or usefulness of herbs, by preparing medicinal compounds from them, by preserving them so that they are always available and by finding new ways to release their active constituents.

          Increased efficiency in extraction leads directly to a reduction in material wastage and power ultrasound has been shown to improve extraction from plant materials. The classical techniques for extraction are mainly liquid-solid extraction by means of steam and/or organic solvents. All such techniques use relatively high temperatures and thus the energy consumption is very high and decomposition of some compounds may also occur. The use of ultrasound avoids these high temperatures and can result in enhanced component extraction at lower temperatures and in a faster time.

            Plants are a source of raw chemical materials and there are real possibilities for the growing crops for specific extracts. One of the best known examples is the rubber tree. It also well known that oil plants like sunflower, rape, castor, could be not only a source of food material but also a bulk source of chemicals for the cosmetic and chemical industries. Some examples are: linalool from coriander, limonene and carvone from dill seeds, anethole from fennel seeds and α-pinene which can be separated from turpentine oil extracted from coniferous trees in quite large amounts.

1.      Comparison of conventional and ultrasonically assisted extractions of pharmaceutically active compounds from Salvia Officinalis, M.Sali¨ovل, ¦.Toma and T.J.Mason, Ultrasonics Sonochemistry, 4, pp 131-134 (1997).

2.      Ultrasonically assisted extraction of bioactive principles from plants and their constituents, M.Vinatoru, M.Toma and T.J.Mason, Advances in Sonochemistry, 5, ed. T.J.Mason, JAI Press, pp 209-248 (1999)

3.      Towards the industrial production of medicinal tincture by ultrasound assisted extraction, P.Valachovic, A. Pechova, T.J.Mason, Ultrasonics Sonochemistry, 8, pp 111-118 (2001).

4.      Potential for the use of ultrasound in the extraction of antioxidants from Rosmarinus officinalis for the food and pharmaceutical industry, S.Albu, E.Joyce, L.Paniwnyk, J.P.Lorimer and T.J.Mason,. Ultrasonics Sonochemistry 11, pp 261-265  (2004).

Examples of Projects

“The extraction of Rutin from Sophora Japonica using ultrasound”

“The effect of various parameters and techniques on the efficiency of extraction of antioxidant materials from the herb Rosmarinus Officinalis”

“Extraction and analysis of anti-inflammatory agents from blueberries”

“Improved Extraction of Antioxidants and Flavonoids from Natural Materials”

MATERIALS SCIENCE: POLYMER SCIENCE AND TECHNOLOGY

There are several ways in which ultrasound has been used in Polymer science and technology.

Molecular Weight Reduction - Polymer Degradation

It has been known for some time that long chain molecules are broken down by ultrasonic waves. Although the exact mechanism by which this occurs is open to question, it is generally agreed that it is the hydrodynamic forces that are of primary importance. It is also believed that ultrasonic degradation, unlike chemical or thermal decomposition, is a non-random process with cleavage taking place at roughly the centre of the molecule and with larger macromolecules degrading the fastest. The consequence of this is that the larger molecules are preferentially degraded. It is also known that there is a limiting molecular weight below which degradation does not take place. This limiting molecular weight has the added effect of narrowing the molecular weight distribution.

Polymer Synthesis

Early investigations into the use of ultrasound in polymer synthesis involved sonicating solutions containing a polymer and a monomer. Polymerisation was thought to be affected by utilising the shock wave energy, released on bubble collapse, to homolytically break a carbon-carbon bond in the polymer's backbone thereby producing a radical entity which could attack the monomer and polymerise by a conventional mechanism. The sonochemical generation of radicals has also been utilised to improve emulsion polymerisation

Polymer Encapsulation

Over the past 30 or so years there has been a general interest in the development of technologies for the encapsulation of fine inorganic powders with organic polymers. The general aim of encapsulation is to affect the physical properties of such powders particularly in terms of increasing their dispersability in solvents or in composite phases. For example, if the end use of the powder is to be in either the coating field or the production of speciality films, then the two factors which dictate optimum physical properties are firstly an even and small particle size of the original powder, and secondly a uniform coating of each and every particle.

Most paint formulations contain TiO₂ pigment particles produced by ball milling.  Unfortunately during storage there is a problem with the re-agglommeration of the TiO₂ pigment which ultimately leads to poor coverage and a patchy appearance of the final paint product. By applying ultrasound to TiO₂  pigment in an emulsion system (water, surfactant and monomer) we were able to show that it was possible to produce the “ideal” pigment for formulation purposes where each particle was separated from its neighbour and was totally covered with polymer and had no tendency to reagglomorate (see figure below).

In the absence of ultrasound                                                  in the presence of ultrasound

Plastics Technology

There are at present only a few commercial applications of ultrasound in the plastics industry.  The best known is probably the welding of thermoplastics, a process which lends itself readily to automation.  In the process ultrasound is applied to two layers of plastic, heat is generated at the interface causing the material to soften, and flow, and the two layers are subsequently glued or joined together.

The effect of ultrasound on the encapsulation of titanium dioxide pigment, J.P.Lorimer, T.J.Mason and D.Kershaw, Colloid and Polymer Science, 269, 392‑397, 1991.

The use of ultrasound for the controlled degradation of polymer solutions, Advances in Sonochemistry Vol 1 G.J.Price (pp231-287) ed. T.J.Mason, JAI Press 1990

Sonochemical initiation of polymerization, Advances in Sonochemistry Vol 2 P.Kruus (pp1-22) ed. T.J.Mason, JAI Press 1991

Examples of Projects

“The effect of ultrasound on the polymerisation of N-vinylcarbazole”

"The effect of ultrasound on the emulsion polymerisation of styrene"

"Ultrasonic degradation of dextran in aqueous solutions"

MATERIAL SCIENCE: THE PREPARATION OF NANOMATERIALS

There are close to 20 different methods for the fabrication of nanomaterials, these are regarded as the chemical and engineering materials of the future. What makes the use of power ultrasound effective and different from the other methods of synthesis are properties such as:

·                    The ability to produce nanomaterials in the amorphous state. This is of particular importance in catalysis, magnetism, coatings etc.

·                    The shorter reaction times involved e.g. mesoporous materials (MSPM) can be prepared in hours (it normally takes days by the sol–gel method).

·                    The insertion of nanoparticles into the pores of MSPM without blockage of the pores.

·                    The syntheses of inorganic fullerenes at room temperature. Other methods normally require high temperatures.

Power ultrasound provides one of the most exciting ways to synthesize pure and supported nanomaterials for research and industry. This is due to the high temperatures and pressures created during the collapse of an acoustic cavitation bubble is on a microsecond time scale and is associated with a rapid cooling rate (> 10⁹ K/s) which is much greater than that obtained by conventional rapid cooling techniques (10⁵-10⁶ K/s). This means that sonochemistry can be used to prepare amorphous nanosized metallic particles. Also, since the thermal conductivities of metal oxides are generally much lower than those of the metals, these faster cooling rates are necessary to prepare amorphous metal oxides.

The Sonochemistry Centre is involved in the preparation of nanoparticles through an EU STREP programme entitled “Development of multifunctional nanometallic particles by Sonoelectrochemistry” (SELECTNANO). SELECTNANO aims to manufacture new metal and transition metal nanoparticles for dedicated new applications, using the novel process of sonoelectrochemistry..This technique is a specialism of the Centre and combines electrolysis with sonolysis. The sonication horn serves as a cathode for the electrolysis process and as a transducer releasing ultrasonic waves.

A short electric pulse serve to reduce ionic species and deposit seed nanoparticulate metal crystals on the cathode. This is followed by a short ultrasonic pulse causing these nanoparticles to fbe released into the electrolysis mixture. Repeated sequential pulse then provide a semi-continuous method of generating the metallic powders.

This technique will be applied to fabricate nano Mg, Al, Fe, Co, Cr as well as nano alloys such as Fe-Cr, Fe-Mn, Fe-Co, and Cu-Sn which are foreseen to have a wide range of applications. Once formed, these nanoparticles can also be adsorbed onto stabilizing matrices such as colloidal dispersions using surfactants and polymers.

Applications for such materials include:

·                    Multifunctional printing; (conductive labels and information coding based on a printed pattern for security purposes

·                    nanostructured metallic coating

·                    sized shell structures for controlled release of encapsulated active materials

·                    molecular diagnostics and bio separations

·                    high intensity color pigments; novel cosmetic ingredients

·                    Nanoscale conductive structuring materials

·                    Novel coating additives

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