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POLYHYDROXYALKANOATE (PHA) PRODUCTION FROM METHANE & NATURAL GAS - LITERATURE REVIEW PART 1

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POLYHYDROXYALKANOATE (PHA) PRODUCTION FROM METHANE & NATURAL GAS - LITERATURE REVIEW PART 1

Wed, 04/03/2019 - 15:41
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Plastics Pollution

Section 1: The Plastic Problem

1.1 The History of Plastics

In the past century, plastics have saturated our world and changed the course of our lives. Plastics (or polymers) in general are organic materials that are malleable and can be molded into different shapes. The arrival of synthetic plastics was a valuable discovery that opened doors for producers to create limitless new products and presented a breakthrough from the material constraints of the natural world. Fig. 1 highlights some key milestones in this revolutionary discovery [1] [2] [3] [4]. Humans have been using natural plastics as far back as the Iron Age. Medieval craftsmen used animal horn – a keratin product – to make lantern windows [5]. Gutta Percha (a natural resin from the bark of Malayan trees) made electrification possible when it was used to coat cables for telecommunication and it revolutionized the golf game when it was introduced for making golf balls. It wasn’t until the 18th century that Charles Goodyear invented the process of vulcanization for rubber, which made possible the rubber tire for the bicycle and then the motor vehicle [2,3,5]. The biggest breakthrough and the birth of the modern plastics happened when the first synthetic plastic – Bakelite – was discovered in 1907 by Baekeland. This work lead to the discovery of polystyrene, polyvinylchloride (PVC), nylon and several other synthetic plastics still used today.

 

The plastics industry expanded after these discoveries, mostly driven by war efforts since plastics were used to manufacture most military supplies [2,3,5,6]. In the late 1900s, the oil crisis struck, crude oil prices skyrocketed and so did the prices of synthetic plastics [3]. Moreover, in 1969, two major oil pollution incidents occurred. In January of that year, an oilrig ruptured along the coast of Santa Barbara, California causing one of the largest oil spill to date in the US waters. While later in June of the same year, the Cuyahoga River in Ohio - which had been polluted for decades with industrial waste - caught on fire and led to great damage in the city of Ohio. These incidents raised concerns about pollution and awareness about the environmental implications of synthetic plastics, causing the plastics reputation to fall. ICI-UK took up this challenge and in 1990 launched the first biodegradable polymer – Biopol – made from plant sugars and glucose, with the potential of mitigating the oil pollution issues [3]. Several others have made efforts ever since then to create a variety of biopolymers. Nonetheless, synthetic polymer production has evolved with advanced processing techniques and these polymers continue to be produced today. These synthetic polymers are cheap to produce and promise to last forever. Unfortunately, they cause too many problems especially when the user no longer needs them, and these issues need to be resolved.

Plastics FIGURE 1

1.2 Effects of Plastics in the Environment and on Human Health 

Plastics have several benefits including their durability and low cost of production, making them ideal for many applications. They help to reduce food waste by keeping products fresh for longer periods of time, are essential in most types of packing and building materials, have improved transportation efficiency, and have great potential for use in renewable energy technologies. In 2013, 299 million tons were produced worldwide, representing a 4 percent increase from 2012. The majority of plastics are derived from petrochemicals such as fossil fuels and gas, and annually, approximately 4 percent of petroleum is used worldwide to produce plastics with another 4 percent used to power their manufacturing process [7,8].

 

However, synthetic plastics do not degrade when thrown away in a landfill, making up almost 13% of the municipal waste stream. With nowhere to go, they end up occupying large amounts of space [9]. More often than not, incineration is used for their disposal, which emits elevated CO2 concentrations into the atmosphere, contributing to climate change effects, and generates toxic compounds such as PCBs, BPA, dioxin, styrene, etc. [10]. Only 9% of all plastics are recycled because the recycling systems are quite demanding in the degree of purity and high sorting accuracy required. Additionally, the recycled polymer resin is usually of a lower quality compared to the virgin polymer [10,11].

 

Therefore, the reputation of synthetic plastics continues to suffer due to rising environmental concerns and potential associated health threats related to its usage. The National Oceanic and Atmospheric Administration (NOAA) reported that plastic marine debris are the major types of debris seen deposited as micro-particles along the coastline [12]. These plastic marine debris do not degrade, and are becoming one of the most persistent pollutant problems facing the world’s oceans and water bodies. When marine animals ingest these micro-plastics, they can become malnourished or starve to death due to blockage in their digestive systems and about 267 animal species to date have been identified with this problem. Plastic debris also accumulates pollutants such as polychlorinated biphenyls (PCBs), which could potentially seep into the organisms that eat the debris. However, it is very difficult to quantify the exact impact of these pollutants to the organism and more research is needed for clarification [13]. Furthermore, in 2005, approximately 269 boating accidents and 15 deaths were caused by collision with floating and submerged debris [13]. In order to preserve our marine ecosystem it is imperative that this plastic issue be addressed.

 

Polymer resins are usually mixed with various additives to improve their performance. Additives such are plasticizer are used to make the polymer more pliable, coloring is sometimes added to make multicolor products, inorganic filler such as carbon and silica are added to strengthen the products, and other additives such as flame retardants and thermal stabilizers are also used. Some of these additives – such as lead, phthalates and biphenol A (BPA) – are potentially toxic and there is still controversy around their effects on humans [14]. Studies have shown that phthalates and BPA can be detected in aquatic environments, in dust and the air, which raises severe concern about their effects on human health [15,16]. Other studies have used biomonitoring techniques to measure the concentration of environmental contaminates in human tissue and this research has shown that phthalates and BPA, alongside other plastic additives, are present in the human population. Even though exposure is mainly through house dust, other uptake routes include foodstuff and to a lesser extent oral drugs, inhalation and ingestion [15,17]. There is some evidence showing the negative correlation between phthalate metabolites and semen quality in adults [18].

 

A recent study has also shown a significant relationship between urine levels of BPA and cardiovascular disease, type 2 diabetes and abnormalities in the liver enzyme [19]. There is now a growing concern about the high exposure to both BPA and phthalates for premature infants undergoing neonatal intensive care [20]. Other identified health concerns include impacts on brain development, reproductive systems and effects on thyroid hormones. In all these cases, detrimental effects could be caused by exposure to both low and acute doses of these chemicals but the migration of the chemicals into the human population is yet to be ascertained. However, evidence on the impact of plastic chemical additives on humans is still limited and further research is needed to establish the relationship with those chemicals that seep out of the plastics [14]. Regardless, it is important to emphasize the potential risks these additives present in order to start identifying preventive measures.

Despite all the rising concerns, plastics remain integral to our daily lives. Plastics have made possible the development of most technological devices including advancements in medicine. Since it is obvious that plastics play a significant role in our lives and continue to be a necessary part of our future, investigating alternative options for synthetic plastics is crucial.

 

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