1119-1104 Evolution of the Nigerian Polymer and Paper Bank Notes; the Challenges of Cost-Benefit and Structure – Property Advantages

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs ISSN: 1119-1104 EVOLUTION OF THE NIGERIAN POLYMER AND PAPER BANK NOTES; THE CHALLENGES OF COST-BENEFIT AND STRUCTURE – PROPERTY ADVANTAGES

*1Dalen, M. B., 2Ibrahim,. A. Q.,. 3Adamu, H. M. and 3Chindo, I. Y. 1.Department of Pure and Industrial Chemistry, University of Jos, Nigeria 2. Environmental Management Technology Programme, School of Environmental Technology, ATBU Bauchi, Nigeria 3Chemistry Programme, School of Science, ATBU Bauchi, Nigeria Email: [email protected]

(Received 14th May 2013; Accepted 4th September 2013)

ABSTRACT Synthetic polymers have become an indispensable part of our everyday life since their introduction over 100 years ago. This paper highlights the application and utilization of polymers in medicine, food and agriculture, housing and environment, engineering, electrical and electronics, particularly the use of biaxially oriented polypropylene (BOPP), a crystalline conformer that exists in monoclinic, hexagonal and trigonal shapes in the production of films for banknotes which in Nigeria today is facing photo-degradation challenges resulting to fading and brittleness. These challenges have prompted the Central Bank of Nigeria (CBN) to contemplate the scrapping of the polymer notes. The paper examines and compares cellulose, a natural polymer and a base material used for “paper” banknotes with BOPP, a synthetic polymer utilized for “polymer” banknotes in terms of physical and chemicals properties, ease of incorporation of security features amongst others in the light of the present challenges. The evolution of money in Nigeria from British West Africa to date is also highlighted.

INTRODUCTION affordable prices. (Cowie, 1973, Walker – It is well known that there are three (3) basic Homes, 1975). needs of man; food, shelter and clothing (Nkeonye, 1990). However, if man depends In housing and domestic environment, only on natural sources such as cotton, wool, synthetic polymeric products have replaced silk, hides and skins for clothing, sourcing most of the traditional materials for roofing, for these materials for the over six (6) billion wall clothing, furniture, table cloth, flooring people in the world today would definitely (tiles/rugs) and structural fittings such as have tasked the human productive ability. To doors, windows, sinks, baths and water solve this problem, human intellect therefore cistern at reduced cost and enhanced invented such synthetic fibres as nylons, aesthetic appeal (Obande, 1991). polyethylene terepthalate (PET), teflon (polytetrafloroethylene-PTFE), creslan In food and agriculture: Packaging and (polyacrylonitrile), vestolen, ulastron, storage of products are achieved almost polyethylene (PE), polypropylene(PP) et exclusively with the use of plastic bags, films certra. These are used as fabrics, braiding and containers. Polyvinylchloride (PVC), PE cordage, bristles, yatch sails and protective and woven PP are used extensively here clothing and in many of these applications (Walker – Homes, 1975). Furthermore, they out – perform the natural fibers buried perforated plastic pipes are (Nkeonye, 1990). At present, it is not always extensively used to drain and aerate marshy easy to distinguish visually between the soils for improved crop yield. Similarly, footwear made of natural leather from that fertilizers are being formulated with soluble made of synthetic leather materials which and biodegradable plastics to provide slow- provide comfort to millions of people at release media in order to save costs and check soil pollution (Onyido et al, 2012).

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs In medicine: Almost all equipments in of 58% (Blythe, 1980). In 1988 alone, an hospitals are made of one form of polymer or estimated 45,400 tones was used as the other ranging from stethoscope, compared to 4,500 tones for 1983. Polymers polyamide surgical sutures, to the complex with conjugated double bonds have been machines. Furthermore, damaged blood found to conduct electricity and heat due to vessels can be replaced using plastic pipes the presence of delocalized π-electrons, and a few bones can also be replaced with such polymers include polyacetylene, plastic mouldings. The target now is to polyphenylenesulphide and replace lungs, kidneys and liver with plastics. Polyparaphenylene, amongst others (Dyson, In addition, biodegradable plastics have been 1992). It is also worth mentioning their developed as slow drug- release agents so applications in areas such as photo- that diabetic patients no longer need to be conductors in electro-reprographic industry, subjected to the discomfort of daily insulin non-linear optics in telecommunication intake as well as intake of contraceptives for industry, that is frequency doublers, photo- family planning (Dyson, 1992). resists (sensitizers in screen printing). Their pyroelectric, piezoelectric and ferroelectric In electrical, electronics and audiovisual: properties have been employed in such Polymers are typically utilized in electrical applications as sonar hydrophone, ultrasonic and electronic application as insulators transducers, pyroelectric sensory, audio where advantage is taken of their very high frequency transducers and electro- volume resistivity of 108 - 1016 ohm/m as mechanical devices. Polydiacetylene and against 108 - 1012 for ceramics and 10-8 - 10-4 polyvinylidine floride (PVDF) have been ohm/m for typical conductors. For this used in this regard. PVDF in particular has reason a very thin costing of plastics such as generated much interest in application in PTFE is sufficient to withstand thousands of medical imaging because of the close volts at high temperatures (Marshal, 1978). acoustic impedance match between it and body tissues (Marshal, 1978, Dyson, 1992). Similar uses include cable sheathing, dielectric layers, and films for printed In engineering: Polymers have contributed circuit substrates and semi-conductors. tremendously to the field of engineering, Encapsulants from PTFE, PE, PVC which ranges from the vulcanization of combine rare qualities of very high natural rubber to mouldable formations resistivities and adequate mechanical useful for making rain coats, water-proof performance at extreme frequencies, boots, solid tyres to high load bearing glass temperatures and chemical environment and fibre-reinforced plastics (Punmia, et al, would continue to provide the bedrock 2001). Natural and synthetic rubbers are used necessary for any foreseeable advancement in several applications such as carpets, cover in the electrical, electronics and audio- for chairs, car bodies etc. Similarly the visual industry. PVC in particular is being adhesive and surface coating industries have used for audio-disc, tapes and video discs grown astronomically as a result of early making pocket video recorders, and cameras patented works of Hugo Backland et al perfect achievements (Kawai, 1984). (1907) on phenolic formaldehyde (PF), urea formaldehyde (UF), melamine formaldehyde Some other polymers also exhibit typical (MF) resins (Obande, 1991). The bond properties such as strength, flexibility, strength of these adhesives compares elasticity, stability, mouldability and ease of favourably with that of steel. These handling have increased research and characteristics are employed in aircraft, development have led to the production of spacecraft and building industries, as well as conductive polymers. In the United States in the shoe and allied industries. The molded of America, the use of conductive plastics resins provide excellent workings for the has been predicted to grow at an annual rate electrical, furniture and domestic ware

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs industries; for example, highly transparent administration. The pounds and shillings were acrylic sheets, polymethyl methacrylate changed to Naira (N) and kobo (K), and three (PMMA) – perspex were developed in the denominations of notes were issued as follows; 1930s to replace glass for many applications N1; N5 and N10. In response to rapid because of its light weight, low cost and ease economic growth made possible by the oil of fabrication. Though it has not completely boom, N20, and N50 note denominations were replaced inorganic glass because of its poor added in 1977 and 1991 respectively. abrasion resistance, research is in progress to Considering cost effectiveness and expansion improve this deficiency (Obande 1991, Kani of economic activities, higher denomination and Kani 2005). Similarly in the automobile notes were issued. These were the 100 Naira industry, polypropylene is used for the note (1999) and 200 Naira note (2000). The production of under bonnet and interior parts, 500 Naira note was released in April, 2001 mainly by injection or blow mouldings which while the 1000 Naira note was released in th are coloured, durable, light and cheaper to October, 2005. On February 28 2007, as part produce than metal fabrications (Punmia et al, of the economic reforms, N50, N20, N10 and 2001). N5 banknotes and N1 and 5K coins, were reissued in new designs, while N2 coin was In the construction industry, plastic materials introduced (CBN, 2009). continue to provide better substitutes for ceramics and metals especially in pipes, gears HISTORY OF POLYMER BANK NOTES and component housing, mainly because of In 1983, Costa Rica and Haiti issued the first their ease of processing, greater resistance to Tyvek and the Isle of Man issued her first corrosion and lightness. The furniture industry Bradvek polymer (or plastic) banknotes; these continues to rely more on plastics as were printed by the American Banknote substitutes for wood, it is obvious that with Company and developed by DuPont dwindling forest reserves, wooden furniture Corporation of France (IPCA April, 2002). In could someday become extinct (Edoziem, 1988, after significant research and 1979). development by the Commonwealth Scientific and Industrial Research Organization (CSIRO) EVOLUTION OF MONEY IN NIGERIA and the Reserve Bank of Australia (RBA), The West African Currency Board was Australia produced the first polymer banknote responsible for issuing currency notes in made from biaxially-oriented polypropylene Nigeria from 1912 to 1959. Prior to the (BOPP), and in 1996 became the first country establishment of the West African Currency to have a full set of circulating polymer Board, Nigeria had used various forms of banknotes of all denominations (Enajekpo, money, including cowries and manilas. On 2003). Apart from Australia, other countries July 1st, 1959 the Central Bank of Nigeria such as Vietnam, Brunei, New Zealand, Papua issued Nigerian currency notes and coins and New Guinea, Romania etc, have all their . the West African Currency Board notes and circulating banknotes on polymer Since then, coins were withdrawn. It was not until 1st July, other countries to adopt circulating polymer 1962 that the legal tender status was banknotes include Bangladesh, Brazil, Brunei, withdrawn from West Africa Currency Board Chile, Indonesia, Israel, Malaysia, Mexico, (CBN, 2009). In 1963, Nigeria became a Nepal, New Zealand, Papua New Guinea, Republic, and this eventually led to the Romania, Singapore, the Solomon Islands, Sri changing of the banknotes in 1965 to reflect Lanka, Thailand, Vietnam, Samoa and Zambia, the country‟s new status. The notes were again with other countries issuing commemorative changed in 1968 following the misuse of the polymer notes, including China, Kuwait, country‟s currency notes, during the civil war Northern Ireland, Taiwan and Hong Kong. At (CBN, 2009, Vitafoam News, 2008). that time, other countries indicated a plan to issue polymer banknotes includes Nigeria and In 1973, Nigeria adopted a truly national Canada. In 2005, Bulgaria issued the world‟s currency in decimal form instead of the first hybrid paper-polymer banknote ( pounds, to replace the imperial system which www.CBM.com). Nigeria issued her first she inherited from the British colonial polymer currency in 2007, starting with the

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs N20 note and in 2009 introduced the N5, N10 and N50 notes (CBN, 2009).

Table1: Countries that introduced Polymer banknotes with dates. Source: IPCA (April, 2002), International / polymer currency Association Bulletin. S/No Country Year of First S/No Country Year of First Note Note 1 CostaRica/Man 1983 15 Bangladesh 2000 Island 2 Singapore 1990 16 Brazil 2000 3 Papua New Guinea 1991 17 China 2001 4 Western Samoa 1991 18 Solomon Islands 2001 5 Kuwait 1993 19 Vietnam 2001 6 Indonesia 1994 20 Mexico 2002 7 Breunei Darussalam 1996 21 Nepal 2002 8 Thailand 1996 22 Zambia 2003 9 Malaysia 1998 23 Chile 2004 10 Sri Lanka 1998 24 Guatemala 2007 11 New Zealand 1999 25 Hong Kong 2007 12 Northern Ireland 1999 26 Nigeria 2007/2009 13 Romania 1999 14 Taiwan 1999 27 Chile 2010

WHY “POLYMER” BANK NOTES Opacifying- Two layers of ink (usually WERE INTRODUCED white) are applied to each side of the note, Polymer bank notes were developed to except for area(s) deliberately left clear for increase the security of Australia‟s paper creating an OVD. currency against counterfeiting. In 1967, forgeries of the Australian $10 notes were Sheeting- The substrate is cut into two found in circulation and the RBA was sheets suitable for the printing press. concerned about an increase in counterfeiting with the release of color photocopiers that Printing- traditional offset, intaglio and leer year. In 1968, the RBA started collaborations press printing processes are used. with the CSIRO and funds were made available in 1969 for the experimental Over coating- notes are coated with a production of distinctive papers. The protective varnish. insertion of an optically variable device (OVD) created from diffraction gratings in BOPP is a non-fibrous and non-porous plastic as a security device inserted in polymer compared to paper banknotes. Bank banknotes was proposed in 1972. The first notes using BOPP are more durable, harder patent arising from the development of to tear, more resistant to folding, more polymer banknotes was filed in 1973. In resistant o soil, water proof (and washing 1974, the technique of lamination used to machine proof), easier to machine process, combine materials; the all- plastic laminate shredable and recyclable at the end of their eventually chosen was a clear BOPP lives (http://www.polymer notes, Org/other laminate in which OVDs could be inserted Country). Furthermore, due to problems associated with the “paper” currency notes without needing to punch holes (www.CBM.com) The BOPP substrate is which includes dampness, low resistance to processed through the following steps: tear, stress, rubbing and staining, the “polymer” currency was introduced for

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs superior physical property advantages such counterfeiters (www.CBM.com ; IPCA, as tactile feel, tensile strength, tear 2002). resistance, resistance to staining and impervious to water over those of the ADOPTION OF POLYMER BANK “paper”( Enajekpo, 2003). NOTES As of 2011, countries that have converted Apart from improving durability over fully to polymer bank notes include; “paper”, polymer banknotes were developed Australia, Brunei, Bermuda, New Zealand, to prevent counterfeiting through Papua New Guinea, Romania and Vietnam. incorporated security features such as Other countries and regions with notes OVDs that are extremely difficult to printed on guardian polymer in circulation reproduce (Abraham and include; Brazil, Bangladesh, Canada, Chile, Waterman,1972).The traditional printed Dominican Republic, Hong Kong (for a two- security feature applied on paper can also be year trial), Indonesia, Israel, Malaysia, applied on polymer. These features include Mexico, Nepal, Nigeria, Solomon Islands (no intaglio, offset and letter press printing, longer issued), Sri Lanka, Thailand, Samoa, latent images, micro-printing and intricate Singapore and Zambia. Canada released its background patterns. Polymer notes can be first polymer bank note ($100) on 14th of different colors on the obverse and November, 2011, followed by the $50 bank reverse sides. note on the 26th of March, 2012 and the $20 bank note on 7th November, 2012. Countries Like paper currency, polymer bank notes can and regions that have issued commemorative incorporate a water mark (an optically bank notes (which are not in circulation) on variable “shadow image”) in the polymer Guardian polymer include: China, Taiwan, substrate. Shadow images can be created by Kuwait, Northern Ireland and Singapore. the application of optically variable ink (www.CBM.com). (OVI) enhancing its fidelity and color shift characteristics. Security thread can also be ORIGIN OF TERM “POLYMER” BANK embedded in the polymer notes; they may be NOTES magnetic, fluorescent, phosphorescent, micro The term “polymer” in place of “plastic” to printed, clear text as well as windowed. Like describe banknotes was introduced by the paper, the polymer can also be embossed Reserve Bank of Australia (RBA) at the (Charles, 2007). launch of its $10 note on 1st November 1993. Jeffrey Bentley-Johnson and his firm were Polymer notes also allow new security retained to assist in the launch of the $10 features unavailable on paper such as note after a cold reception for the preceding transparent windows and diffraction grating $5 note. He held the view that “plastic” and to be incorporated. Since 2006, however, the “bank note” were close to being oxymoronic. development of the paper transparency Having earlier worked in a firm that window technologies by De La Rue (optiks) designed and constructed synthetic fibre and G&D (Varifeye) have reduced that plants, he recognized the polymer nature of advantage (IPCA, 2002). The transparent the new bank note and so proposed the use of window where the OVD is located is a key the term (IPCA, 2002). The transition from security feature of the polymer bank note. It plastic to polymer is evidenced in the launch is easily identifiable, allowing anyone to be of the $5 note in July1992 (Plastic) to the able to authenticate a bank note. Because launch of the $10 note in November, 1993 polymer bank notes contain many security (polymer). This was documented on the features that cannot be successfully launch TV commercials viewable on the reproduced by photocopying or scanning, it RBA website (http://www.polymer notes. is very difficult to counterfeit. The Org /other Country). complexities of counterfeiting polymer notes are proposed to act as a deterrent to

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs CONFIGURATION OF bonds that cannot be altered by physical POLYPROPYLENE means except by breaking and reforming the Polypropylene is recognized as a robust, chemical bonds such as C-C, C=C, and CC. durable and light weight product and as such Polypropylene is a linear hydrocarbon is an ideal carrier for security documents polymer containing little or no unsaturation. (www.CBM.com). Polypropylene was first The significant influence of the methyl group polymerized by Karl Rehn and Natta in is that it can lead to products of different March 1954 serving as a preliminary work tacticity, ranging from completely isotactic for large scale synthesis from 1957 onwards. and syndiotactic structures to atactic At first it was thought that it would be molecules giving products with different cheaper than polyethylene. An important physical properties (Billmeyer, 1984). concept in understanding the links between the structure of polypropylene and it‟s Isotactic Configuration properties is tacticity (Billmeyer, 1984). The This configuration can be described as alternating orientation of each methyl group polymers that have a single sequential (CH3) relative to the other methyl groups on arrangement of repeat units. Isotactic the neighboring polymer chain which has a Polypropylene is a polymer of considerable strong effect on the finished polymer‟s commercial importance and several studies ability to form crystals because each methyl have been made on its crystalline structure group takes up space and constrains back and properties of the various solid phase. bond bending (MCGraw,1975, These studies have shown that the material Enajekpo,2003). can easily form a random phase and can be easily converted to crystallined form Configuration can be defined as the (Enajekpo, 2003; Structure X). arrangement of atoms fixed by chemical

Structure X: Isotactic polypropylene

Syndiotactic confirmation: In this units. It has little or no commercial value configuration, there is an alternation in the (Billmeyer, 1984) arrangement of methyl groups on the repeat unit. The arrangement is such that each PHYSICAL AND CHEMICAL methyl group attached to a particular carbon PROPERTIES OF POLYPROPYLENE (PP) becomes the mirror image of an opposite Most commercial polypropylene is isotactic methyl group. (Structure X) and has an intermediate level of crystallinity between that of low density 3 Atactic Configuration: Is a random polypropylene (LDPE, 0.915g/cm ) and high 3 distribution of the methyl group on repeat density polyethylene (HDPE, 1.35g/cm ).

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs It‟s young‟s modulus is also intermediate. available in many profiles Polypropylene is normally tough and flexible vi. Propylene is autoclaveable for usage in especially when co-polymerized with bio-hazardous environments ethylene. This allows polypropylene to be vii Other uses include fittings and used as an engineering plastic, competing connectors, storage containers, sinks, with materials such as Acrylonitrile, and hoods. Butadiene-Styrene (ABS) rubber (Rubber viii The best joining method is hot air or World, 1983). nitrogen welding. Can be mechanically joined with screws or rivets. Ultrasonic inserts work well (www.dynalabcorp.com) Polypropylene, a polymer prepared catalytically from propylene which differs Polypropylene Quick Facts: from HDPE by having an isotactic replacement  Maximum Temperature: 135°C of a hydrogen atom by a methyl group on  Minimum Temperature: 0°C alternate carbon atoms in the main chain.  Hardness: R95 Although largely unreactive chemically, the  UV Resistance: Poor presence of the methyl groups  Autoclaveable; yes makes polypropylene slightly more susceptible  Polypropylene Repeat unit :CH CH to attack by strong oxidizing agents than 2 3 CHn HDPE. A major advantage is polypropylene's 3 higher temperature resistance, which makes it  Density:Amorphous=0.855g/cm , particularly suitable for items such as trays, crystalline(monoclinic,hexagonal,trigo nal)=0.946g/cm3 funnels, pails, bottles, carboys and instrument o jars that have to be sterilized frequently for use  Melting point :160-170 C in a clinical environment. Polypropylene is a  Rigid translucent material with excellent mechanical  Tensile Strength:4500 psi (High stress properties and has gradually replaced the Bearing) polyethylenes for many purposes.  Translucent (www.dynalabcorp.com).  Glass transition Temperature; -20oC o  Degrade temperature; 260-270 C PP Resistance:  Poly Olefin inertness and low dielectric losses. i. Excellent resistance (no attack) to dilute and concentrated acids, alcohols, bases and mineral oils CELLULOSE, A BASE MATERIAL USED FOR “PAPER” BANKNOTES ii. Good resistance (minor attack) to Cellulose is a natural polymer with the formula aldehydes, esters, aliphatic (C6H10O5)n. It is the permanent structure of plant hydrocarbons, ketones and vegetable cell walls mainly and chemically composed of oils ,D-linked polycondensate glucose units linked iii. Limited resistance (moderate attack together in 1,4 position by oxygen in glycosidic and suitable for short term use only) to linkages (Crawford, 1981, Structures Y and Z). aromatic and halogenated hydrocarbons and oxidizing agents iv. Great chemical resistance makes polypropylene a popular choice for plating and chemical tanks, as well as laboratory cabinetry and semi- conductor bench tops v. This material machines well and is

Structure Y: -D glucose (cellulose repeat unit)

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs

Structure Z: Cellulose polymer chain (Klemm, et. al., 2005

Cellulose is the structural component of the and stabilizers in processed foods. Cellulose primary cell wall of green plants, many powder is for example used in Kraft's forms of algae and the oomycetes. Some Parmesan cheese to prevent caking inside the species of bacteria secrete it to form tube (Weiner and Lois, 2000). Cellulose biofilms. Cellulose is the most common insulation made from recycled paper is organic compound on Earth. About 33% of becoming popular as an environmentally all plant matter is cellulose. Cellulose (E460) preferable material for building insulation. It is mostly prepared from wood pulp (the can be treated with boric acid as a fire cellulose content of cotton fiber is 90%, that retardant. Cellulose consists of crystalline of wood is 40–50% and that of dried hemp is and amorphous regions. By treating it with approximately 45% (Cellulose, 2008). strong acid, the amorphous regions can be broken up, thereby producing nanocrystalline For industrial use, cellulose today is mainly cellulose, a novel material with many obtained from wood pulp and cotton. It is desirable properties. Recently, mainly used to produce paperboard, paper, nanocrystalline cellulose was used as the cardstock and textiles made from cotton and filler phase in bio-based polymer matrices to linen and to a smaller extent it is converted produce nanocomposites with superior into a wide variety of derivative products thermal and mechanical properties (Peng et such as cellophane and rayon (Lawrence and al, 2011). Rina, 2008). Both cellophane and rayon are known as "regenerated cellulose fibers" and Physical properties of Cellulose are identical to cellulose in chemical structure and are usually made from Molecular (C6H10O5)n dissolving pulp via viscose. A more recent formula and environmentally friendly method to Appearance White powder produce a form of rayon is the Lyocell Density 1.5g/cm3 process. Melting point Decomposes at 320oC Solubility (water) None Cellulose is the raw material in the Crystalline forms Monoclinic and manufacture of nitrocellulose (cellulose triclinic nitrate) which is used in smokeless gunpowder and as the base material for celluloid used for photographic and movie films until the mid-1930s.(Peng et al, 2011). MOLECULAR STRUCTURE OF Cellulose is used to make water-soluble CELLULOSE adhesives and binders such as methyl cellulose and carboxymethyl cellulose which Cellulose is an insoluble molecule consisting are used in wallpaper paste. Microcrystalline of between 2000 - 14000 residues with some cellulose and powdered cellulose are used as preparations being somewhat shorter. It inactive fillers in tablets and as thickeners

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs forms crystals (cellulose Iα) where intra- heated beyond 60–70 °C in water (as in molecular (O3-H O5' and O6 H-O2') cooking), cellulose requires a temperature of and intra-strand (O6-H O3') hydrogen 320 °C and pressure of 25 MPa to become bonds holds the network flat allowing the amorphous in water (Deguchi, et al, 2006; more hydrophobic ribbon faces to stack. David and Roy, 2008). Weak C6-H O2' hydrogen bonds may also make some contribution to the crystal Many properties of cellulose depend on its stability. Cellulose has no taste, is odorless, chain length or degree of polymerization, the is hydrophilic with the contact angle of 20– number of glucose units that make up one 30, is insoluble in water and most organic polymer molecule. Cellulose from wood pulp solvents, is chiral and is biodegradable. It has typical chain lengths between 300 and can be broken down chemically into its 1700 units; cotton and other plant fibers as glucose units by treating it with concentrated well as bacterial cellulose have chain lengths acids at high temperature. The overall ranging from 800 to 10,000 units (Peng, et structure is of aggregated particles with al, 2011). Molecules with very small chain extensive pores capable of holding relatively length resulting from the breakdown of large amounts of water by capillarity cellulose are known as cellodextrins; in (Charles, 2007). contrast to long-chain cellulose, cellodextrins are typically soluble in water and organic The natural crystal is made up from solvents. Cellulolysis is the process of metastable Cellulose I with all the cellulose breaking down cellulose into smaller strands parallel and no inter-sheet hydrogen polysaccharides or completely into glucose bonding. This cellulose I (that is, natural units; this is a hydrolysis reaction. Because cellulose) contains two coexisting phases cellulose molecules bind strongly to each cellulose Iα (triclinic) and cellulose Iβ other, cellulolysis is relatively difficult (monoclinic) in varying proportions compared to the breakdown of other dependent on its origin; Iα being found more polysaccharides. Plant-derived cellulose is in algae and bacteria whilst Iβ is the major usually found in a mixture with form in higher plants. Cellulose is derived hemicellulose, lignin, pectin and other from D-glucose units, which condense substances, while microbial cellulose is quite through β(1→4)-glycosidic bonds. This pure, has a much higher water content, and linkage motif contrasts with that for α(1→4)- consists of long chains. Cellulose is soluble glycosidic bonds present in starch, glycogen, in cupriethylenediamine (CED), and other carbohydrates. Cellulose is a cadmiumethylenediamine (Cadoxen), N- straight chain polymer: unlike starch, no methylmorpholine N-oxide and lithium coiling or branching occurs, and the chloride / dimethylformamide. This is used molecule adopts an extended and rather stiff in the production of regenerated celluloses rod-like conformation, aided by the (such as viscose and cellophane) from equatorial conformation of the glucose dissolving pulp (Stenius, 2000). residues. The multiple hydroxyl groups on the glucose from one chain form hydrogen ADVANTAGES OF “POLYMER” OVER bonds with oxygen atoms on the same or on “PAPER” BANKNOTES a neighbor chain, holding the chains firmly Polypropylene can be made translucent when together side-by-side and forming uncoloured but is not readily made microfibrils with high tensile strength. This transparent as polystyrene, acrylic and strength is important in cell walls, where the certain other plastic. It is often opaque or microfibrils are meshed into a carbohydrate coloured using pigment. Polypropylene has matrix, conferring rigidity to plant cells. good resistance to fatique and is commonly Compared to starch, cellulose is also much recycled with the number “5” as its resin more crystalline. Whereas starch undergoes a identification code (Table 2; Dalen and crystalline to amorphous transition when Nasir, 2009).

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs While polymer currency technology was and house hold chemicals as mentioned originally developed to make counterfeiting earlier. This enhanced durability has resulted more difficult and costly; it also has in a big reduction in the number of notes advantage over paper currency in terms of required and therefore printing costs for the durability and recycle value (Table 2). notes. Imperviousness to water and the Polymer notes no longer fit for use are longer life span of polymer note also mean granulated and then melted and blended into less waste compared with “paper” notes. To pellets. These pellets are the raw materials achieve maximum cost and operational for recycling, a range of environmentally savings in both note issue and note handling friendly products can be produced using and also provide clean and secure bank note polymer pellets including garden items such to the public. It also reduces the cost of as compost bins, plumbing supplies as grease replacing dirty notes which leads to the traps and house building items including reduction in cost thereby free resources that brink and roof shingles. The synthetic could be used for other commitments (IPCA, polymer substrate is more robust and 2002). resistant to damage from moisture, dirt, oils

Table 2: Simple methods for identification of plastics; Source: Braun, 1982 Resin Resin Name Common Uses Examples of recycled products Code 1 Polyethylene Soft drink bottles, peanut Liquid soap bottle, strapping, Terephthalate (PET) butter jars, salad dressing fiberfill for winter coats, bottles, mouth was jars. surfboards, paint brushes, fuzz on tennis balls, soft drink bottles, film 2 High density Milk, water and juice Soft drinks based cups, flower Polyethylene (HDPE) containers, grocery bags, toys, pots, drain pipes, signs, stadium liquid detergent bottles. seats, trash cans, recycling bins, traffic barrier cones, golf bag liners, toys. 3 Polyvinyl chloride Clear food packaging, Floor mats, pipes, hoses, mud flaps (PVC) shampoo bottles 4 Low density Bread bags, frozen bags, Garbage can liners, grocery bags, polyethylene (LDPE) grocery bags multipurpose bags 5 Polypropylene (PP) Ketch-up bottle, yoghurt Manhole steps, paint buckets, containers, margarine, tubes, automobile battery parts, video medicine bottles, polymer cassettes storage cases, lawn notes mower wheels. Etc 6 Polystyrene (PS) Video cassette case, compact License plate holders, golf course disk jackets, coffee cups, and septic systems, desk top cutlery, fast-food sandwich accessories, hanging files, trash container, cafeterias trays cans.

DISADVANTAGES OF POLYMER 1977, Stuctures ZA). The rate and extent of BANKNOTES; Photo-degradation: the structural deterioration process is largely A serious technological problem associated determined by the mechanical integrity of the with polymeric materials (particularly polyblend, its chemical constitution and the polyblends) in their service life is that of variety, concentration and severity of the structural deterioration engendered by attacking species. The resistance of numerous interaction processes taking place polyblends to the effect of degradative within the polymer or polyblend matrix, in agencies, mainly heat, light and oxygen, is the presence of degradation agents (McNeil,

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs therefore regarded as an important parameter necessary towards assessing the for accessing blend quality. technological value and importance of polyblends in their service life. In particular, Thus the selective matching of miscible or the thermal stability of polyblends has been compatible polymer pairs and the study of the subject of several previous studies the stability of their polyblends against (Yusuf, 1996). prolonged exposure to degradation agents are

Structures ZA: Polymer bank notes prone to photo-degradation

Photo degradation takes place as a result of in an eventual fall in the rate of hydroxyl exposure of polymer currency to UV build-up in the system (Yusuf, 1996). The radiation such as that present in sun light following schemes are suggested, to account (McNeil, 1977; Yusuf, 1996). The ability to for the chemical transformations photo-degrade increases as the wavelength of accompanying photo oxidative degradation the incident radiation decreases, that is, as of polypropylene. Yusuf (1996) investigated the energy of the quanta increases. Photo infra-red evidences from thermal studies of degradation is widely recognized to proceed PVAc-PEMA observed that PVAc degraded via free radical mechanism (Encyclopedia of via autocatalytic decomposition process Polymer Science and Tech. 2006). involving the molecular elimination of ethanoic acid as reported by some previous A characteristic feature of the oxidative workers. On the other hand, observed degradation of polymers is the formation of persistent discoloration of PVAc during carbonyl compounds. The initial increase in exposure is an indication of the presence of hydroxyl concentration is attributed to conjugation. increase in the rate of formation of hydroxyl species, in the form of hydro peroxides, due Therefore the generation of radicals by auto- to the onset of degradation reactions that oxidation could set in leading to the probably involved radical attack and formation of hydro peroxides and carbonyls. subsequent auto-oxidation of polypropylene Auto oxidation is a more likely phenomenon polymer substrate. The hydroperoxides than direct disproportionation into monomer, formed are converted to carbonyls, resulting which should be the case if the polymer were

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs degraded in vacuum (McCallum and Schoff, oxygen is very small in the reaction medium. 1972).Chain scission reactions of the type It is possible to have reactions (3),(4) playing discussed above are believed to be a more important role. responsible for the pronounced deterioration observed. Initiation: Initiation also follows from the formation of All polymers degrade with or without the second reaction. Once this hydro- oxygen; the reaction is faster because it is peroxide is formed other reactions follow usually auto- accelerating that is oxygen whether by thermolysis or photolysis. acts as a catalyst and the process is such that initially the degradation in air is slow but ∆H   later accelerates at a constant value. If one ROOH RO + O H …… (6) adds an initiator, it would remove or reduce hv the slow auto-accelerating induction time, ROOH RO + OH .....… (7) but if one adds an anti-oxidant or a stabilizer this will extend the auto acceleration Because RO and OH can effectively extract induction time. RH hydrogen atom

Oxygen usually exists in the triplet state or   RO ROH + R ……….. (8a) di-radical (O=O, O-O). This is the state in RH which oxygen is injurious to a polymer and OH HOH + R ……….. (8b) accounts for more of radical degradation of the polymer in air. The sequence of the reaction (8a) and (8b) further inject radicals in the reaction medium and which goes back and initiate. It is known that reactions (6) and (7) R + O ROO ………………… (1) 2 are catalyzed by some metal ions such as   manganese, copper and cobalt ions. ROO + RH ROOH + R ………(2) ROOH + M+ RO + OH- +M2+ ….(9) 1st reaction occurs readily because of very low activation energy, where R= alkyl or ROOH + M2+ ROO + H+ + M+ ..(10) aryl. 2nd reaction occurs less readily because it involves a carbon-hydrogen scission Since little or no hydro-peroxide is present at therefore it has a higher activation energy. In the beginning of the anti-oxidation, the rate nd most polymers, the 2 reaction is the rate of oxidation increases in the characteristic  determining step (rds) except when R is auto accelerating manner as the resonance stabilized such as 2, 6-dimethyl concentration of hydro-peroxide builds up in hepta-2,5-diene. the system (curve a). Addition of trans-metal ion or hydro-peroxide reduces or removes Termination reactions in auto oxidation the auto-accelerating part of the curve given occurs by 3 routes for a short time at least a linear rate of oxidation due to stationary hydro-peroxide 2R R-R ……. (3) concentration. This would arise because reactions (6) and (7) are equivalent to R + ROO ROOR …….. (4) reaction (2). Commercial polymers do not behave the same because of additives such as  2ROO ROOR + O2 …………… (5) fillers, e.t.c (Peters and Still, 1996).

Since reaction (2) is rate determining step In auto-acceleration, the most useful tool to (RDS) (5) will be the termination stage but monitor the rate of degradation by infra-red

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs spectroscopy in the region of 1710-1735 cm-1 The hydroxyl component in the early stages which characterizes; can be measured because they give broad 1720 cm-1 for C=O absorption which are not very useful as a 1735 cm-1 for CHO result of hydrogen bonding. The presence of 1710 cm-1 for COOH any of those groups indicates the chemical changes occurring in auto-acceleration.

Brittle(b) Hydroperoxide thermosets Ceramics Ductile/malleable(a) Pure polymer metals (iron), steel etc

Stress

obsorbed obsorbed

2 O

Elastomers; Natural and synthetic rubbers

Temperature Strain Fig. 1 : Temperature vs absorbed Oxygen on degradation of polymers (a = pure polymer; b = hydro-peroxide is added; c = anti-oxidant is added). This simple curve shows the ideal behavior of a hydrocarbon being oxidized in air.

∆H  RH/O CH2CH2CH2 CH2CHCH2CH CH2CHCH2CH2+ OH -CH2CHO + CH2CH2 2 -CH2C = O

OOH O OOH

-CH2C = O

OH ……….(11)

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs Polymers of different chemical structures behave differently in their resistance to degradative oxidation.

CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2

X – C – OO + H – C – X X – C – O – O – H – C X – C – O – O – H – C X –C – OOH + C – X

CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 ;;(

….(12)

Depending on x, the carbon atom carrying the labile hydrogen in the transition state, a partial ionic charge, positive or negative or a combination of all these.

In hydrocarbon polymers the oxidation increases in this way.

-CH2- < -CH- < CH- < -CH2CH = CH- < -CH = CHCH2- …………. (13)

Other substituents such as methyl, the releasing also makes the polymer to be more susceptible to oxidation. In polymers containing hetero atoms, polarity dominates and the rate of oxidation decreases in this series (Yusuf, 1996) CH3 F F

CCH2 > -CH2NHCO-CH2 >-CH2OCO > -CH- > -CH > C- > CH > C-C

COOCH3 COOCH3 COOH CN F F ………………….. (14)

Apart from the fundamental structures, other standard orifice at a given time and factors such as minor impurities may also temperature and is inversely proportional to determine their oxidative stability e.g. low the mole weight) of polymers (Roger, 1979). density polyethylene contains more branches than the high density polyehylene, therefore MFI  1/molecular weight …… (15) it breaks slower (Peters and Still, 1996). Oxidation of commercial polymers Most commercial polymers are stable to The Physical Effect of Auto-oxidation degradation at a fair temperature as The most pronounced effect of auto- polymerized. The problem however is during oxidation is the reduction in molar mass their conversion to useful products where which affects physical properties. Chain they are subjected to high temperatures and scission is one of the most important high shearing in the melt state because it is consequence of the auto-oxidation of completely impossible to exclude oxygen at polymers which occurs in the -, alkoxy high temperature, the important radical bearing compounds as C- C-O which modifications in the chemical structure of a have twice as many chains. This chain is polymer occur. This will have a profound measured by viscosity or melt flow index, effect on the subsequent service MFI (amount of polymer extruded through a performance. The fabricating process

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs involves melting the polymer to a liquid molecule. Benzoquinone is one of the which is then extruded through a die or into a most efficient radical acceptors mould (Yusuf, 1996). During extrusion, the known in the polymer industry and polymer is continuously mixed by means of when it is added it causes rapid a screw. Thus at this stage the polymer degradation. The mechanism of undergoes shearing and temperature effects stabilization was further confirmed in which reduces the molecular weight of the natural rubber when it was shown polymer to give micro-radicals which initiate that in both rubber containing degradation. There are four evidences which diphenylpicrylhydrazyl and a confirm these micro-radical formation; polystyrene containing 1,1- dinaphthyl disulphide, it was found (a) Radical scavengers are known to that the number of terminal bearing have a great effect on the reaction. At chains of these compound correspond ordinary temperatures, micro radicals to the number of chains which was are also found but because oxygen is measured by decrease in molar mass. excluded, the micro radicals simply In natural rubber, the weakest bonds recombine. Whereas at the other are those between the isoprene units stage where there is oxygen or a because the radicals so formed are radical scavenger, they combine with stabilized by allylic resonance these micro radicals to form a stable

  -C-CH=CHCH2CH2-C=CH2CH- -CH2C=CH CH2 + CH2C=CHCH2-

CH3 CH3 CH3 CH3 ………….. (16)

(b) If the polymer is degraded in the presence of a vinyl monomer and in the absence of oxygen, a block copolymer is formed as in scheme 1.

– C – CH = CH CH2CH2C = CH2CH – – CH2 – C = CHCH2

CH CH3 CH3 3 CH3

+ CH2 = C – COOMe

CH3

– CH2 – C = CHCH2OOH – C = CHCH2 – CH2 – C

CH COOMe 3 CH3 n

Scheme 1: Degradation of natural rubber ……(17) If the two polymers are mixed together under the stirring effect and again in the absence of oxygen, block copolymers (eqn. 17) which will be obtained which confirms the formation of micro radicals. NR = AAAAA AAA + AAA AAABBB

PMMA = BBB BB + BBB …………. (18)

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs Evidence was demonstrated by the presence of radical scavengers e.g. dinaphthyl disulphide and mercaptobenzylthiazole is labeled with radioactive isotopes. It was discovered that the polymer developed radioactivity (Peters and Still, 1996).

(b) Electron Spin Resonance Technique: This technique has confirmed radical formation and suggested their attachments at the end of the polymer chain as accepted from chain scission (McNeil, 1977).

shear   -CH2-C-CH2C- nCH2-C + CH2-C -CH2-C-CH2-C CH2-C-CH-C + CH3-C- …………….. (19)

Specific examples

Polyvinylchloride and Poly olefins The reduction in molar mass which occurs in natural rubber (NR) during compounding is not a serious problem because it is during that, that vulcanization and additives are added to convert the NR to cross links. For thermoplastics, this could be dangerous because the hydro peroxide links formed can act as a source of weak link during service life of the polymer (Polymer Science and Technology, 2008). This is problem with polypropylene (PP) which undergoes an increase in melt flow index during processing whereas polyethylene‟s MFI decreases due to cross linking. In both cases however the shearing is similar as discussed for NR (McNeil, 1977).

OOH Me Me . . . RO. . O2/RH . – CH – CH – CH (R )– C CH CH – – CCH CH – – C – CH CH – (RO) + OH 2 2 2 (c) 2 (a) (b) . Me CH3 Me Me Me Me O

(e) (d)

. . – C = CH2 + CH – – C = O + CH2 – CH – Me Me Me Me

Chain scission (O2 deficiency) Chain scission (excess O2)

……………….. (20) Scheme 2: Degradation of poly olefins

The difference lies in the subsequent reaction mixer than in a close mixer. In low oxygen of the micro allyl radical after the depletion concentration, PP undergoes of oxygen which both dissolve in the depolymerization, that is reaction “e” polymer and trapped between the polymer whereas polyethylene (PE) undergoes cross molecules. If oxygen is increased linking (Peters and Still, 1996). deliberately, reaction d, predominates tha is peroxide concentration increases with processing time much rapidly in an open

African Journal of Natural Sciences 2013, 16, 1 – 20 www.ajns.org.ng/ojs CONCLUSION AND RECOMMENDATION Braun D; (1982) Simple methods for From the base structures of cellulose and identification of plastics, Macmillan polypropylene and their physical and publishing Co. Inc. New York. chemical property differentials, it is easily observed that cellulose readily absorb BS/3662/2. www.goole.comhttp:llen- moisture (water and other liquids) due to the wikipedia.org/wik.filecopolymers.org presence of free hydroxyl side groups in its accessed on 10-12-2010 structure (Y and Z) while polypropylene exhibits high polyolefinic inertness with high CBN (2009); 50th anniversary News degree of hydrophobicity (X). Magazine. The glycosidic links are lesser in strength compared to the C-C bonds in PP hence has Cellulose (2008). In Encyclopædia higher tear strength than cellulose. However, Britannica, Encyclopædia Britannica the hydrogen atoms on the methyl side Online. Chemical Composition of Wood groups on the chain of the PP are labile and undergo oxidation on exposure to sunlight Charles, A. Bishop, ed. (2007); Vacuum (UV radiation) leading to discoloration and deposition onto webs, films, and foils, brittleness of the polymer base substrate Volume 0, Issue 8155. p. 165. ISBN 0- (McNeil, 1977; Yusuf, 1996). Polymer 8155-1535-9. currency prone to UV-degradation can be stabilized by incorporation of special Cowie, G.M.J (1973); Polymer Chemistry additives commonly known as UV- and Physics of modern materials absorbers. Examples include; carbon black international Textbook Company Ltd, (1-5%), Benzophenone and its derivatives, Bucks. phenyI salicylates and benzotriazoles as well as Ba/ Cd soaps. We strongly believe that Crawford, R. L. (1981); Lignin Federal Governmen of Nigeria (FGN) and biodegradation and transformation. New the Central Bank of Nigeria (CBN) can York: John Wiley and Sons. ISBN 0- engage the expertise of color chemists and 471-05743-6. polymer scientists to solve this problem of photo-degradation of the polymer bank notes Dalen, M.B (2007); The Role of polymer Science and Technology in Agriculture, rather than accepting the CBN‟s recent st planned scrapping of the polymer bank notes Medicine and Engineering in the 21 (Thisday Newspapers May 12th, 2013). Century, Paper presented at a workshop organized by Student Chemical Society REFERENCES of Nigeria, University of Jos. Abram, B.I and Waterman, N. G (1972); Dirty Money, JAMA 219:1202-1203 Dalen, M.B and Nasir, T. (2009). Plastic wastes Recycling, Science World Journal Billmeyer, F.W. Jr (1984), Text book of 4, 1 pp 7-10 Polymer Science; John Willy and sons Inc. David, G. Barkalow and Roy L. Whistler (2008) "Cellulose", in AccessScience, Blythe A.R (1980); in electrical properties of McGraw-Hill, doi:10.1036/1097- polymers, Cambridge university press, 8542.118200. accessed 11 January Cambridge. 2008.

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