Wednesday, April 3, 2019

Product Profile of a Plastic Shopping Bag (HDPE)

Product Profile of a Plastic shop Bag (HDPE)Samantha PearsonPlastic shopping bags/ lean bags be subroutined extensively in forthwiths world. They be produced in many divergent sizes and glosss, determined by its take and marketing campaign of the purchasing firm/industry. Carry bags atomic number 18 do of formative that is flexible and relatively tough1. The plastic is identified as High assiduity poly thereforee (HDPE), indicated by the Voluntary Plastic Container coding System2 (used to identify different plastics for recycling) on the carry bag itself. High tautness polythene is listed as 2 on the coding system2.How HDPE is made polyethylene is made of monomers of ethylene. Monomers of ethylene are obtained from petroleum by a cinch process or by modifying natural gas such as methane or ethane3. polyethylene domiciliate be made into three different types of polymers under different conditions, namely High density polyethylene, Low assiduousness Polyethylene (LDP E) and Linear Low Density Polyethylene (LLDPE). High Density Polyethylene is produced from petroleum and under impression pressure conditions (pressure of about 10-80atm) 3 whereas Low Density Polyethylene is produced under high pressure conditions.At the higher(prenominal) end of the low pressure and higher temperatures (about 80atm and 60-200C) a Phillips throttle valve is used to create an dynamical site for polymerisation6. The process that uses the Phillips particle accelerator is know as the Phillip Process. The Phillips process was made industrial by Phillips Petroleum go with in 19614. A Phillips accelerator is a highly active catalyst made of chromium oxide on silica with a high get up domain of a function. The active site is the chromium carbon bond where the transitional surface (chromium) oxidation state is reduced by a reaction with alkene (a synthetic fibre made from polyethylene) 5 which set outs the active site to a greater extent reactive4. A Phillips cat alyst is prepared before it enters the reactor payable to the complexity of the silica support that needs to be the correct structure for optimum polymerisation5. In a Phillips process plant an ethylene feed sprout is supply into a reactor with a stream of diluted pre-made catalyst. polymerization takes place in the reactor and exits as a slurry. The slurry is then desiccated and pellets are collected at the end4. The advantage of the Phillips process is that the catalyst does non suck up to be deactivated or removed from the slurry as the silica bum increases the activity of the catalyst and all of the catalyst reacts with the monomer ethylene4. Polyethylene with less leg is produced in this process when compared to the Zeigler Natta catalyst process4.At the lower end of the low pressure and lower temperature (about 1-10atm and 60-70C) a Ziegler Natta catalyst is used6. A Ziegler Natta catalyst is a combination of a transition metal compound from Groups IV to septenary and a co-catalyst made of an organometallic compound from Groups I to III. In general titanium tetrachloride or titanium (III) chloride and a trialkylaluminum is used7. The catalyst, like the Phillips catalyst, also needs a support with high surface area magnesium chloride, magnesium chloride or silica as they maximise the surface area and therefore the active sites on the catalyst7. The Zeigler Natta catalyst is prepared in the same reactor as the polymerisation occurs4. In this process an ethylene feed stream is fed into a reactor with feed streams of metal alkyls and Group IV to VI metals (Titanium) forming the catalyst on its support in the reactor. Slurry exits the reactor where the catalyst is deactivated (to upset chains reacting together which cargo areas the molecular pitch distribution fairly constant). The slurry is then dried and power is collected at the end4.In industry today High Density Polyethylene is produced by slurry polymerisation with a silica base catalyst an d the Phillips process is used more often than the Ziegler Natta catalyst process4.Polymerisation MechanismPolymerisation occurs as a free al-Qaeda chain-growth reactions. Chain growth reactions occur as successive linking of monomer molecules to the end of the suppuration chain8 and occur in three grades.Stage one is the initiation demonstrate where a radical reacts with ethylene to produce a monomer radical to run the reaction8R + H2C=CH2 R-H2C-H2C 1.1The rate of initiation is defined by the rate comparability 1.2Where f is the initiator efficiency, I is the molar tightfistedness of the initiator and M is the total tautness of all the chain radicals and kd is the rate constant9.Stage two is the propagation stage where monomer radical adds to an separate(prenominal) monomer radical. The active centre moves to the end of the chain constantly and there is only one active centre at a given time8R-H2C-H2C + H2C=CH2 R-H2C-H2C-H2C-H2C1.3The rate of propagation is defined by th e rate equality 1.4Stage three is the termination stage where chain growth is finish either by two radicals adding together or disproportionation where an atom transfers to another chain9. The rate of termination is defined by the rate equation 1.5The general structure of High Density Polyethylene isFigure 1 social organization of Polyethylene10Figure 2 Structural Formula of Polyethylene10Morphology of HDPE and how it suits a carry bag applicationHigh Density Polyethylene is very a few(prenominal) short branches, if any. This results in the polymer existence more crystalline than amorphous and in some areas of the polymer, it may be crystalline. The glass transition temperature (when the material becomes amorphous) of HDPE is -100C and the melting transition temperature (when the material turns to a liquid phase) is 130C11. These temperatures stag HDPE an ideal polymer to make carry bags out of as the temperature that it is used in is never/rarely over and below these ranges. HDPE has signifi evoketly different properties to other polymers made in similar ways (LDPE and LLDPE). HDPE is flexible, translucent, and weatherproof a proper resistance to chemicals, relatively tough (has a tensile attitude of 0.20-0.40 N/mm2)1. HDPE has a thermal coefficient of expansion of 100-20010-6 and a density of between 0.944 and 0.965g/cm3.1The properties above are all suited for the application of High Density Polyethylene carry bags. A good tensile strength allows for relatively intemperately objects to be placed into the bag without it finishing, small amounts of heat does not counter stir its properties, it is weatherproof, allowing it to get wet with no changes to its properties, the flexibility allows for easy use, storage and functionality whereby it can be crop to create handles. A translucent appearance allows for it the plastic to be coloured as the produces seem fit which they can use for advertising purposes and make the final product aesthetically ap pealing if its purpose needs to be.How the finished product is madeHigh Density Polyethylene pellets are sold by the firm that owns the plant to a maker that produces plastic shopping bags/carry bags. The pellets are melted and mixed until they are completely homogenous mixture. The mixture is then heated to above 350C in a furnace12. The melted mixture vaporises into a tube made of the same mixture (but solid) situated above the furnace and gradually cools down the higher up the tube the vapour gets, where it condenses. Rollers flatten out the tube resulting in a film subdue HDPE. While in the twineing area of the process, the film is cut to the desired/required thickness and collected on a roll. The thickness of the roll of thin plastic film is myrmecophilous on the manufacturing specifications (each roll roughly produces 35000 bags12) and is cut and a new roll starts forming automatically.The completed roll moves onto printing, where the thin film gets a specific colour/patte rn dependent on the consumer. Alcohol based ink (which has to keep flowing to retain its viscosity rate to ensure the same c oncentration is used and all the bags are identical) is used to print on these thin films12. Ink is transferred onto the film by ink rollers. Once printing is done, it is once again rolled up.The printed film then moves to another department where it is cut into the specified sizes and a machine with a punch, punches holes on the one emplacement to make handles. And a sealing machine binds the edges of the bag together through heat12.Additives added to the final productIn some cases to increase the tensile strength of the plastic (for heavy duty carry bags), Low Density Polyethylene may be added to the pellets of HDPE during the melting stage12. Alcohol based ink is added to give the product aesthetic appeal. Biodegradable additives such as prodegradant concentrates (PDCs) 13 which are metal compounds which help the oxidation process of degrading plastic, ad ded to make plastic bags more environmentally friendly. overdue to the application of the product, additives such as UV stabilisers are not needed and plasticisers are not needed due to the flexibility property HDPE already has.Alternative materials to make the productDue to polymers being an environmental hazard, shopping bags/carry bags have been made with chocolate-brown paper (paper bags). However this does not have the desired properties as they break easily and are not weatherproof and they do not have any chemical resistance to them.Advantages of using HDPEHigh Density Polyethylene (HDPE) is a polyethylene thermoplastic. Thermoplastics soften, when heated, to a liquid and flow and harden, when cooled, to a solid. They can undergo this heating and cooling cycle (curing process) which little to no change in the final product the process is reversible as no chemical bonds are formed or broken14. This results in the plastic being easily recycled.The product can be aestheticall y modified.Remoulding and reshaping can be done to them14.Weatherproof and chemically resistantHigh-impact resistanceLight weightDisadvantages of using HDPEHDPE is not biodegradable. Due to their light weight they can nose candy away in the wind and travel relatively far, causing befoulment and many environmental hazards to living organisms.If heated they will meltThermoplastics fly the coop to me more expensive than thermosets14Recycling HDPE needs an economic incentive as it can be more expensive to recycle plastic than to make new ones2.ReferencesBritish Plastics Federation. (2015). Polyethylene (High Density) HDPE. forthcoming http// give out accessed 2015/05/20.P Gaylard. (2009). razz 1. Polymer Science. University of Witwatersrand. p. 5, 27.P Lepoutre. The Manufacture of Polyethylene. getable http// Last accessed 2015/05/20.Buffalo School. High Density Polyethylene. Available http//w Last accessed 2015/05/20.KBR. (2015). Olefins. Available http// Last accessed 2015/05/20.P Gaylard. (2009). lecture 10. Polymer Science. University of Witwatersrand. p. 3.P Gaylard. (2009). Lecture 8. Polymer Science. University of Witwatersrand. p. 9-12.P Gaylard. (2009). Lecture 2. Polymer Science. University of Witwatersrand. p. 3.P Gaylard. (2009). Lecture 6. Polymer Science. University of Witwatersrand. p. 23-33.Macrog. Polyethylene. Available http// Last accessed 2015/05/20.Michigan State University. (2013). Polymers. Available http// Last accessed 2015/05/20. stripping Channel (2010). How its made Plastic Bag Episode. Available https// mention?v=8CfL5xl2N1Q Last Accessed 2015/05/20Maria Trimarchi Vicki M. Giuggio. (2009). Top 10 Eco-friendly Substitutes for Plastic. Available http/ / Last accessed 2015/05/20Mordor Plastics. (2015). Thermosets vs Thermoplastics. Available http// Last accessed 2015/05/20.2015

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.