There are everyday plastics around us, an example would be Polylactic Acid and Polystyrene. Polylactic Acid (PLA) is a type of plastic that is a biodegradable polymer that can be produced from existing manufacturing equipment such as designed for petrochemical industry plastics.
PLA is different than most thermoplastic polymers because most plastics are derived from the distillation and polymerization of nonrenewable petroleum reserves while PLA is derived from renewable resources like corn starch or sugar cane. Plastics that are derived from biomass (e.g.
PLA) are known as “bioplastics.” Polylactic acid is therefore used for making items as diverse as packaging materials, consumer items such as disposable plates and cups. Chemical Formula : (C3H4O2) To make Polylactic Acid, corn or other raw materials undergo fermentation in producing lactic acid which is then polymerized. So far polylactic acid is the most common bioplastic in use today. Briefly, PLA is based on agricultural (crop growing), biological fermentation and chemical polymerization sciences and technologies. During polymerisation, the OH on the acid group (CO2H) group of the monomer reacts with the OH group on the second carbon atom of another monomer. This is an esterification reaction and involves in the loss of water.The production of Polylactic acid through chemical processes goes through 2-hydroxy propionic acid, the single monomer of PLA produced via fermentation or chemical synthesis.
Its 2 optically active configurations, the L(+) and D(?) stereoisomers are produced by bacterial (homofermentative and heterofermentative) fermentation of carbohydrates. Industrial lactic acid production utilizes the lactic fermentation process rather than synthesis because the synthetic routes have many major limitations, including limited capacity due to the dependency on a by-product of another process, inability to only make the desirable L-lactic acid stereoisomer, and high manufacturing costs (Datta and Henry 2006). Polylactic acid polymer film was degraded in abiotic and biotic environments to understand the role of microbes in the degradation process of lactic acid based polymers. The degradation were conducted in a well-characterized biotic and abiotic system in an environment maintained at 40, 50 and 60 degrees C in a sterile aqueous and desiccated environment system. The combination of experiments in different environments isolated the distinct effect of microbes, water, and temperature on the morphological changes in the polymer during degradation. the PLA matrix degrades upon melt processing thus affecting the thermo-mechanical features of the blended material. In this work, we studied the effect of processing at high temperature on the molecular weight distribution, morphology, and thermo-mechanical properties.
There is a lack of availability of radiolabeled PLA and to that additional techniques were used to observe the changes in the rate and mechanism of its degradation. These applied CO2 evolved, weight loss, molecular weights measured to evaluate the extent of degradation.In order to monitor the morphological changes in the polymer, X-ray diffraction and differential scanning calorimetry techniques are to be used.
To be able to gather some information about the degradative process, FTIR was used as a semiquantitative tool. Neither of the two analytical techniques showed any difference in the rate or mechanism of degradation attributable to the presence of microorganisms. Which then the rate of degradation increased at higher process temperatures.
FTIR data were evaluated for significant statistical difference by t-test hypothesis.Hydrolysis of ester linkage is the primary mechanism of the degradation of PLA as results were confirmed. POLYSTYRENE Polystyrene is a thermoplastic polymer and is also one of the most widely used plastics, the scale of its production successfully being several billion kilograms per year. It can also be used as protective packaging, lid bottles, containers, trays and disposable cutlery.
Styrene is the building block (monomer) of polystyrene and is obtained from crude oil. A range of processes are required to transform the crude oil into styrene such as such as distillation, steam-cracking and dehydrogenation. Styrene will polymerise spontaneously on heating in an oxygen-free atmosphere in order to ensure complete polymerisation at lower temperatures catalysts are also added.
Processes have been designed to aid heat transfer from the exothermic reaction, this is done because it may lead to low molecular weight polymers being formed if not controlled.As researched, Styrene is obtained by reacting ethylene with benzene in the presence of aluminum chloride to produce ethylbenzene. Benzene vapour and ethene are mixed and passed over an acid catalyst, at 650 K and 20 atm pressure. Then the benzene group is dehydrogenated to produce phenyl ethylene, or styrene, a clear liquid hydrocarbon with the chemical structure of CH2=CHC6H5. The polymerization of Styrene is through using free-radical initiators in bulk and suspension processes.
Solution and emulsion methods are also employed. Radical polymerization is used to produce polystyrene through the process of addition polymerization. The predominant polymerization technique is continual thermal mass polymerization which is initiated by heat alone. Suspension polymerization is also used. This technique requires the use of an initiator such as dibenzoyl peroxide.The structure of the polymer repeating unit can be represented as:Chemical Formula : (C8H8)n Melt Temperature : 210-249 degrees celsius Polystyrene is one of the most widely used plastics, with its uses including protective packaging, containers, bottles, trays and disposable cutlery.
Polystyrene is a vinyl polymer that is structured into a long hydrocarbon chain with a phenyl group attached to every other carbon atom. The pendant phenyl (C6H5) groups is key to the properties of polystyrene. It is composed only of the monomer styrene in combination with itself. Depending on the type of Polystyrene it can be classified as a ‘thermoplastic’ or a ‘thermoset’ material. Polystyrene starts with the distillation of hydrocarbon fuels into lighter groups called “fractions” which some are combined with other catalysts to produce plastics through the process of polymerisation.Therefore is produced by free radical vinyl polymerization, from the monomer styrene.The thermal degradation of polystyrene is at 350 degrees celsius made by kinetic studies and different pressures. “The degradation rates determined from the amount of oily products were strongly dependent on the agitation speed and the initial load as well as on the operating pressure.
” The effects of these can be distinguished by the change of mass transfer resistance from the molten polymer to gaseous stream. “The decrease in degree of polymerisation occurring either with evolution of low molecular weights at a higher temperature or with negligible volatilization at lower temperatures.” Research says during their tests, the results suggest that below 300°C, the breakage of the polymer chains is random, and involves also a minor fraction of some abnormal, unidentified structures.
“Above 300°C, an extensive intermolecular transfer process seems to be the main cause of the decrease in degree of polymerisation, whereas an overall depolymerisation of 100 structural units at each chain scission is the source of volatilisation.” (Guaita, 1986). With everyday plastics around us, there can be environmental impact from them. Comparing to both Poly Lactic Acid and Polystyrene polymers both can have different individual impact on the environment. Most common use for PLA is packaging including plastic bottles and plastic silverware cups.
As researched It is therefore, classified as generally recognized as safe (GRAS) by the United State Food and Drug Administration (FDA) and is safe for all food packaging applications (Conn and others 1995; FDA 2002). However because of its production these plastics later end up in landfills, where they take years to break down. But it can also be a great use because that means plastic bottles can degrade in landfills where people don’t recycle. “PLA exhibits several physical and mechanical properties that make it more difficult to use than PHAs or other plastic options for applications outside of biomedicine.” (Kristen Flint, 2013). Another advantage would be if most bottles are made of PLA this will be biodegraded which would cause no problem with pollution and would may reduce environmental impact. The huge benefit of PLA as a bioplastic is its versatility and the fact that it naturally degrades when exposed to the environment. For example, a PLA bottle left in the ocean would typically degrade in six to 24 months.
Accordingly, there is a high potential for PLA to be very useful in short lifespan applications where biodegradability is highly beneficial (e.g. as a plastic water bottle or as a container for fruit and vegetables).Many people are not aware of the harmful effects of Polystyrene. Polystyrene is one of those materials that’s everywhere around us, such as the gadgets around us. “Polystyrene contains the toxic substances Styrene and Benzene, suspected carcinogens and neurotoxins that can be hazardous to humans.
” Because Polystyrene products are made with petroleum, which can cause a non-sustainable heavy polluting resource, polystyrene can also have consequences in the environment such as its effect on global warming. “It’s environmental impacts were the second highest, in the product manufacturing process as well as the use and disposal of the products, energy consumption, greenhouse gas effect, and total environmental effect, according to the California Integrated Waste Management Board” (Future Centre Trust, 2010) Also, extruded polystyrene is usually made with hydro chlorofluorocarbons blowing agents which can have effects on the ozone depletion and global warming. Even though their effect on ozone depletion is greatly reduced, though it still has greater effect on global warming than carbon dioxide. To conclude, through complicated production of both polymers, both can be useful in their own ways as it can be used in our everyday life especially to the manufacturing companies. Even if they may impact the environment they can be great uses as plastic utensils, bottles, biodegradable medical resources and such gadgets around us in everyday needs.