1.1 Background study
Packagingvusing plasticvmaterialsvhas rapidly increasedvin recent times. Its vusevcovers a wide area of applicationvfromvautomobile parts, food, drinks, water, snacks, cloths, fresh and sea foods, vfarm products, vmedicals and pharmaceuticals, to mention but a few. The use of such bombasticvamount of schematicvplastics and itsvadvantage overvother packaging materialsvis due tovits diversevandvadvancevpropertiesvofvlongevity.Thevproperties include resistance tovchemicalvreaction, vthermal strength, mechanical and its tensile strength, vespeciallyvenzymaticvreactions (Ezeoha and Ezenwanne, 2013.).
For example it willvtake avveryvlongvtimevsay avhundredvyears to degradevjustva piece of plastic film (polyethene) used to package snacks (gala) at standard environmental conditions. vBasically, two challenges have been cited with the of conventional polyethene usevits dependence on vpetroleum and the problem vof waste disposal. Most of today’s conventionalvsynthetic polymers vare producedvfromvpetrochemicals that vare not biodegradable. Thesevstable vpolymers are a significant vsourcevof venvironmental pollution, vharming vorganic naturevwhen vthey are dispersedvin thevenvironment, changes thevcarbon dioxide cycle, problemvassociatedvwith increasedvtoxic emission. The sources of synthetic polymersvsuch as fossilvfuel and gas arevnow stimulated by environmental concerns. Scientists arevresearchingvdifferentvmethods ofvimprovingvplastics thatvcanvbevusedvmorevefficientlyvsuchvthat they could be recycled, vreused and to possiblyvdegradevafter use.
Alternationvisvtowardsvgreenervagriculturalvsources, vwhich valsovwouldvlead vto the reduction of CO2 emissions (Narayan, 2001). According to the Biodegradable ProductsvInstitutev (BPI), avbiodegradable plastics isvone in which degradation results from the vactionvofvnaturallyvoccurring vmicro-organismsvsuch as bacteria, vfungi or algae. Degradablevplastics are classified byvAmericanvSociety forvTesting and Materials (ASTM) into four these are:-
(1) Photodegradablevplastics: Degradation of the plastic results from natural daylight.
(2) Oxidativevdegradable plastics: A degradation of plastics as a result of oxidation.
(3) hydrolytically degradable plastics: – The degradability resultsvfromvhydrolysis, vand
(4) BiodegradablevPlastics: – Degradablevplastics invwhich there isvbreakdown of long chain polymervmoleculevinto smaller or shorter lengths. It undergoes oxidationvwhich is triggered by heat, ultraviolent light (UVlight), and mechanical stress. Itvoccurs in thevpresencevof moisture and actions from naturallyvoccurringvmicroorganismsvsuch asvbacterial, fungi and algae. (ASTM Standards, 1998)
Thevvariousvdegradablevplastics definitions classified above offers the onlyvproducts whichvarevnaturallyvdegradable. Starch isvbeenvdiscoveredvamongst all biopolymers as a high potentialvmaterial for biodegrablevfilms. Starchvconsists of two types of polysaccharides, amylose and amylopectinvdepending on the sucrose (10-20%) amylase and (80-90%) amylopectin. The hydrophlicity ofvstarch canvbe used tovincrease the biodegrability of starch-basedvplastics. Amylosevis avlinearvmolecule with a fewvbranches, whereasvamylopectinvis avhighlyvbranchedvmolecule. Therefore, vamylosevcontentvis an importantvfactor to biodegrable plastic filmvstrength. Branchedvstructure of amylopectin generallyvleads to filmvwith lowvmechanical properties. To improve thevflexibilityvof plastics, plasticizers arevadded tovreduce internalvhydrogen bondvbetweenvpolymer chainsvwhile increasing molecular space. The mostvcommonly used starchvplasticizers are polyols, sorbitol and glycerol. Thevkey emphasisvin biodegrability is thatvbiopolymer materialsvbreakdownvintovsmaller compounds, either chemically or byvorganisms sooner than synthetic plastics (Bastioli, 2005.). Biodegradablevpackagingvmaterials are materials that degrades back tovthe earth surfacevharmlessly when disposed. This help largely in reducingvthe amount of packaging materialsvthat goes back into landfills andvfurthermore, saves energy, as the biodegrable route requires little or novexternal source of energy its endothermic.
Biodegrable polymervsources are fromvreplaceable agriculturalvfeed socks, vanimal sources, vmarinevfoodvprocessingvindustriesvwaste, or microbial sources. In addition to replenshiable raw agricultural ingredients, biodegrable materials breakdownvinto environmental friendlyvproducts such; as carbon dioxide, vwater and quality compost.
Biodegradationvtakesvplace in two-steps: vdegradation/defragmentationvinitiated by heat, moisture, or microbial enzymes, andvsecond step – biodegradation – where the shorter carbonvchains passvthrough the cellvwalls of the microbesvand are used as anvenergy source. Biodegrable plastics are made from cellulose-based starchvand has been in existence for decades, with first exhibitionvof a cellulose-basedvstarch (which initiated thevbiodegradable plasticvindustry in 1862). Cellophanevisvthevmost cellulose-basedvbiopolymer. vStarch-based biopolymer, which swellvandvdeformvwhen exposedvtovmoisture, include amylose, hydroxyalkanote (PHA), polyhydroxybuterate (PHB), and avcopolymer of PhB and valeric acid (PhB/V). These are made from lactic acid formed fromvmicrobial fermentation of starch derivatives, polylactide does not degrade when exposed tovmoisture (Auras.et al, 2007) PHA, PHB, andvPHB/V are formedvby bacterial actionsvonvstarch (Krochta, 1997). In addition, biodegrable films can also bevproduce from chitosan, vwhich isvderivedvfromvchitin of crustacean and insectvexoskeletons. Chitin is a biopolymervsimilar tovcellulose structure. Therevare variousvwaysvstarchvcan be used for biodegrable polymervproduction;
- Starchvcompostvcontainingvmore than half byvmass of thevplasticizers.
- Biodegrable polymers preparationvusing thevextrusion process of mixtures of granularvstarch.
- Compositionvof starchvwith othervplastics of little quantityvof agricultural based material to enhance the biodegrability of conventional synthetic polymer.
Synthetic polymers can alsovbe madevpartially degradablevbyvblending with biopolymers, vincorporating biodegrable components such as starch, or by adding bioactive compounds. vThe bio compoundsvare degradedvto break thevpolymervinto smaller chains. Bioactivevcompounds work through diverse mechanisms. For example, theyvmay be mixed with swelling agents tovincrease thevmolecular structure ofvthe plastic whichvupon exposure tovmoisture vallow the bioactivevcompounds to breakdownvthe plastics.
1.2 Problem statement
Therevisvbasically, vtwo harmsvconnected to the wide applicationvof synthetic polymer plastics for packaging sincevits inventionvin the 1930s: They arevtotalvreliance on petrochemicalvproduct as itsvmain feedvstockvand the problemvof wastevdisposal. Most of today’s conventional synthetic polymers arevproduced from petrochemicalsvandvare not biodegradable. Thesevstable polymers are avsignificant source ofvenvironmentalvpollution, harmfulvtovorganicvnaturevwhen they are dispersed in the environment. The rawvmaterials such as fossil fuelvand gasvcould be replaced by greenervagriculturalvsources, which contributevto the reductionvof Co2vemissions (Narayan, 2001). Basedvon the abovevit becomes ofvvalue to producevplastics that are biodegradable,vin excess of the past few years syntheticvpolymer usersvhave been introducingvvarious forms ofvbiodegradablevplastics. Thevalternative rawvmaterialsvare nowvfrom plants products, the main amongvmanyvothers is cornvstarch.
Biovplasticsvwere too expensive for considerationvof replacementvfor petroleumvbased plastics. The lowervtemperature needed for the production of bio plastics and the more sTable supply of biomass combined withvthevincreasing cost of crude oil make bio plastics prices morevcompetitivevwithvregular plastics. Starch isvinexpensivevand abundancevin nature, Nigeriavbeing the world largestvproducer of cassava (FAO, 2009) and being a root crop that canvbe grown in every part of the nation, Starchvis totally biodegradable in a wide range of environmentsvand can be usedvin the developmentvof biodegrable packaging products for variousvmarket uses. Incineration of starch product is a way of recycling, the atmosphericvCO2 trapped by starch-producingvplant duringvgrowth, thusvclosing the biological carbonvcycle (Ceredavet al).
The aimvof thisvresearch is to produce biodegrable plastic films from cassava starch used in food packaging, using various additives and plasticizers. This will be achieved via the following objectives.
- Extraction of starch from fresh cassava.
- Improving the extracted starch with addition of plasticizers and various additives,
- Determining the biodegrability and tensile strength of the produced biodegradable products and comparing with that of synthetic polyethene.
- Testing for the validity of the produced biodegradable film.
1.5 Scope of study
The scope of theses work is strictly limited to:
I. Extraction of starch from cassava.
II. Physical and chemical properties of plasticizers and additives in resumption.
III. Cost estimation.
IV. Biodegrability test, and the characterization of the produced film.
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