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A method for converting low density polyethylene into a useful product.


World War II brought about many changes in human consumption. Plastic polymers were refined and their production became widespread during this time due to their low cost and durability (Conner and O'Dell, 1988). Many nations' governments had accommodating attitude toward business during this time and concern of the environmental impact of this consumption had not developed, so it was not an issue of environmental policy (Kubasek et al., 2008). Catastrophic events detrimental to the environment that occurred in the late 1960s and early 1970s, combined with widespread media allowed evidence to surface publicly about the negative effects of human activities on the environment, including the consumption and disposal of plastics (Kubasek et al., 2008).

Because plastic polymers are designed to be durable and long lasting their disposal meant continued persistence in the environment. By the 1970s the persistence of plastics in the environment became recognized as a pollution problem, causing new concerns and challenges for waste disposal management. The implications of the persistence of plastics in the environment have become more apparent in the past few decades with studies focused on plastic debris removed from inland and coastal shorelines.

As more areas have become urbanized, there has been an increase in the amount of plastic waste, as increased urbanization has been found to be positively correlated with dependence on plastic products (Leous et al., 2005). The amounts of plastics that have ended up in the environment are unknown but could exceed billions of tons (Ocean Conservancy, 2010). Post-consumer plastics are introduced directly to the environment through litter and illegal dumping and incidentally through mishandled solid waste.

The lightweight characteristic of plastic permits it to be carried throughout the environment by freshwater streams and storm water drains. It can be deposited onto stream banks or carried to rivers where it may end up in the marine environment. Its existence in the environment has caused a myriad of problems. Plastics and the problems associated with them have been widely studied and it has been found they negatively impact the environment and human health.

Environmental concerns regarding plastic debris include the ingestion by and entanglement of wildlife, transport of toxic chemicals and invasive species, changes in geology in coastal regions, and emissions of greenhouse gases during production, transport, and waste disposal. There have been many deaths of several species of birds, whales, turtles, and other marine species that have been attributed to the consumption of plastic materials. Biologists have reported that at least 50 species of birds have consumed plastics, mistaking them for prey (Day et al., 1985; Pierce et al., 2004). The plastic is incapable of being digested, which can lead to false satiation and ultimately to starvation. The same false satiation has been reported as the cause of death of a beaked whale found dead in Brazil (Secchi and Zarzur, 1999). Filter feeders such as bowhead whales are also at risk of oral entanglement of plastics in the baleen racks (Lambertsen et al., 2005). In addition, leatherback turtles have died as a result of consuming plastic grocery bags (Mrosovsky et al., 2009). It is believed that they mistook them for jellyfish, their principal food source, as they are similar in appearance when suspended in the marine environment. Many deaths of marine species have also been attributed to entanglement in plastic materials at sea. In the Pacific, deaths of monk seals, green sea turtles, and humpback whales were caused by entanglement (Bamford and Carey, 2008.).

A study of four Japanese coastal areas determined that polypropylene (PP) plastic resin pellets either contain or are capable of absorbing polychlorinated biphenyls (PCBs) and dichlorodiphenylethylene (DDE) (Mato et al., 2001). It is believed that this occurs through the attraction of the hydrophobic chemicals to the non-polar surfaces of the thermoplastic resin pellets. Persistent Organic Pollutants (POPs) such as Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) also are hydrophobic and can attach to plastic particles (Saloranta et al., 2006). It is hypothesized that the POPs will be distributed throughout food webs in the future by the consumption of plastic pellets by wildlife, as 60 to 72 percent of floating particulate matter in the Pacific Ocean was found to be plastic (Leous et al., 2005).

Plastic ingestion begins at the most basal of marine food webs. Crustaceans, worms, and barnacles have all been examined ingesting microscopic plastic particles (Beam, 2004). Persistent Organic Pollutants (POPs) attached to these plastic pellets can be passed up to species that ingest these prey. For example, POPs have been both bio-magnified and bio-accumulated in the blubber of marine mammals. They have been detected in the blubber of gray whales, killer whales, Risso's dolphin, and Dall's porpoise (Jarman et al., 1996). These POPs include the organchlorine compounds polychlorinated dibenzo-p-dioxins (PCDD) and dichlorodiphenylethylenes (DDE). POPs have been attributed to reproductive impairment in marine mammals, lowering fecundity rates and creating challenges in the conservation of endangered species.

The transport of invasive species by floating plastic material is another threat that plastic causes. It was discovered that plastics can serve as a vector for invasive species such as fungi and barnacles (Barnes and Milner, 2004). The lightweight and durable characteristics of plastic that have contributed to its commercial success have also created a medium for organisms to raft to alternate ecosystems. Once colonized by fungi or barnacles, the buoyancy of plastic materials allow the species to travel thousands of miles where they could potentially be invasive and disrupt ecosystem processes.

The geology and physical composition of many areas have been altered by the presence of plastics. A study of 18 beaches in the United Kingdom revealed that one third of sediment at these beaches were comprised of microscopic plastic polymers and the concentration had increased over time (Beam, 2004). The Pacific Ocean, north of the Hawaiian Islands now has an artificial island from the accumulation of approximately three million tons of plastic debris (Leous et al., 2005). A study in the Bristol Channel has concluded that the Channel may actually be a sink for plastics that are washed downstream from litter and illegal dumping (Williams and Simmons, 1996). The researchers believe that a build-up of plastics could continue into the future, possibly creating a plastic dam.

Human health is also threatened by plastics. A study in Stockholm showed increases of polybromodiphenyl ethers (PBDEs) in women's breast milk from 1972 to 2000 (Schubert, 2001). Soon after, researchers in North America, Japan, Israel, and Spain found that PBDEs were also present in human tissue and fat. The source of PBDEs is believed to be from flame retardant additives in plastics. Animal studies conducted to assess the threats that PBDEs pose on humans found negative effects on nervous system functioning that was found to increase with age.

Phenolic stabilization additives used in the production of plastics cause a number of problems in humans and have been found to migrate easily from plastics to food (Yamamoto, et al., 2000). A study in 2001 determined that a number of these additives used in plastics have estrogen activity in vitro, suggesting that these additives can serve as an endocrine disruptor (Miller et al., 2001). Later, it was determined that these same additives could cause cancer, as well (Jenkins, et al., 2009). In addition, quaternary ammonium compounds used in plastic manufacturing as anti-static agents or biocides have been found to leach from plastic into biological media (McDonald et al., 2009). These ammonium compounds were found to bind to deoxyribonucleic acid and proteins and were also attributed to infertility in mice.

Plastics have been widely studied and the negative impacts on the environment and human health are well documented. The success of plastic has created long term environmental and waste management policy issues because it accumulates in the environment (Rosen, 1990).

Research has been conducted into degradable plastics. However, the term of biodegradability in regards to plastic is inconsistent as loss of physical integrity is often mistaken for bio-degradation (Palmisanoand Pettigrew, 1992). It is vital to be able to make the distinction between deterioration and bio-degradation as deterioration will not allow plastic to be recycled in the environment and can lead to larger issues as smaller fragment size can distribute plastics more widely. In addition, partial biodegradation can also lead to the release and accumulation of toxic stabilizer chemicals in the environment. Problems have resulted in the processing of plastics that manufacturers claim are bio-degradable and compostable. These problems include the inability to distinguish compostable plastic from others and the rate of


General objective

To investigate the feasibility of converting LDP waste into useful product

Specific objectives

1. To develop a method for converting LDP waste into useful product

2. To establish application of the product developed


Low density polyethylene

Low density polyethylene (LDP) has a high degree of short and long chain branching. It has less strong intermolecular forces as the instantaneous-dipole induced- dipole attraction is less. This results in a lower tensile strength and increased ductility. The high degree of branches with long chains gives molten LDP unique and desirable flow properties.

LDP has the following physical properties; tensile strength is 0.20-0.40 N/[mm.sup.2] and thermal coefficient of expansion is 100-220 x [10.sup.-6] . Its maximum continued use temperature is 65[degrees]C. Its melting point is 115[degrees]C and its density is 0.910-0.940 g/[cm.sup.3]. It has low crystallinity (50-60% crystalline) with main chain containing many side chains of 2-4 carbon atoms leading to irregular packing and low crystallinity (amorphous). It has good transparency since it is more amorphous (has non- crystalline regions) (Saechtling, 1987).

Long drying oil alkyd resin

Long drying oil alkyd resins are prepared using unsaturated oils. They are soluble in aliphatic solvents. They have good brushing characteristics, dry rapidly in air and give reasonably durable, glossy films. Their drying process involves attack by oxygen in the unsaturated regions of the fatty acid residues followed by cross linking (Thomas, 2004; Standeven, 2003).


Kerosene is colorless, thin mineral oil whose density is between 0.75 and 0.85 g/[cm.sup.3]. In paints, kerosene is used as a solvent only when extremely low solvency and slow evaporation are desired. When used as a solvent in paint, it improves the paint brushability, wet-edge and flow by slowing down the over-all evaporation (Potter and Simmons, 1998).

Methodology LDP melting

LDP was melted through heating at 115[degrees]C in a closed system. When some of the melt was put in an air tight container and allowed to cool for 24 hr at room temperature, it solidified into a hard block.

To overcome this problem, there was need to mix the melt with solvent in order to produce a liquefied product at room temperature. Although there are many solvents which could have been used in this study, for example, white spirit, aromatised white spirit, isoparaffins, citrus oil, or turpentine, kerosene was selected for use in the study. Kerosene was used because it improves the paint brushability, wet-edge and flow by slowing down the over-all evaporation as opposed to the other solvents (Potter and Simmons, 1998). Kerosene is a colorless mineral oil, it has density of 0.75-0.85 g/[cm.sub.3], and is a mixture of hydrocarbons [C.sub.9] to [C.sub.16] (Potter and Simmons, 1998).

It was established that a ratio of LDP : Kerosene of 1 : 2 (v/v) would stop solidification of LDP melt on cooling to room temperature (Fig. 1). However, this ratio gave a liquid mixture with suspended solids. To improve this mixture, kerosene was added to LDP melt heated to selected temperatures. The same ratio of LDP : Kerosene of 1 : 2 (v/v) was maintained. Best results were obtained when kerosene was added to LDP melt heated at 210[degrees]C. The resulting mixture was a liquid without any solids at room temperature (Fig. 2).



Brush application of the LDP : Kerosene 1 : 2 (v/v) mixture

The brushing property of the LDP : Kerosene 1 : 2 (v/v) mixture was tested by applying the same on the surfaces of six glass planes. This LDP : Kerosene 1 : 2 (v/v) mixture took 5.83 hr. to dry and on drying formed a film which easily peeled off when gently rubbed.

In order to improve the LDP : Kerosene, 1 : 2 (v/v) adhesive properties, varying amounts of long drying oil alkyd resin (Synald 1070w long oil alkyd) were added. Drying oil alkyd resins contain alkene groups which react with oxygen from the air, resulting to cross linking, hardening, and on drying forms a film (Thomas, 2004; Standeven, 2003). There are many resins which could have been used in this study for example, medium oil alkyd resin, short oil alkyd resin, urethane alkyd resin and polyurethane alkyd resin however, long drying oil alkyd resin (Synald 1070w long oil alkyd) was selected because it is soluble in aliphatic solvents like kerosene, have good brushing properties, dries rapidly in air and gives reasonably durable, glossy films (Thomas, 2004; Standeven, 2003).

It was established that a ratio of LDP : Kerosene : Resin, 1 : 2 : 3 (v/v) mixture gave a dry film that did not crack or peel off when rubbed hard (Fig. 3).


Results and Discussion

To ascertain the quality of the improved liquefied LDP, it was subjected to standards for interior and exterior semi-gloss solvent borne paints according to Kenya Standards by Kenya Bureau of Standards (KEBS) on; application properties, condition in the container, resistance to washing and resistance to accelerated weathering. The quality of the improved liquefied LDP was found to be as follows;

Application properties

The improved liquefied LDP was subjected to the standard test for application properties (KEBS 03-909, 1991). According to this test, it should be easy to brush, should show satisfactory flowing, spreading, leveling and lapping properties. The film when dry should not show signs of sagging, running or streaking and should be free from brush marks. The improved liquefied LDP met all these requirements.

Condition in the container

The improved liquefied LDP was subjected to the standard test for the condition in the container (KEBS 03-910, 1991). According to this test, the sample should be free of gel, coarse particles, foreign matter, skin and be in such condition that at the time of delivery, manual stirring produces a homogenous product of uniform consistency. The improved liquefied LDP met all these requirements.

Resistance to washing

The improved liquefied LDP was subjected to the standard test for the resistance to washing (KEBS 03-909, 1991). According to this test, after curing for 168 hr., the dry film should not wear out after subjecting it to the minimum 4,000 brushing strokes. The improved liquefied LDP met this requirement.

Resistance to accelerated weathering

The improved liquefied LDP was subjected to the standard test for accelerated weathering (KEBS 03-811, 1997). According to this test, the sample should not exhibit any flacking, cracking, chalking or colour fading after testing it in a xenotester apparatus for 42 hr. Each hour was equivalent to 8 days. This implied that the improved liquefied LDP could withstand weathering for over 336 days when applied on glass surface and left exposed to the weather. The improved liquefied LDP met the conditions of the test and this demonstrates that it can withstand harsh weather condition.

Conclusion and Recommendation

Through this research, a method for developing low density polyethylene (LDP) waste into a useful product with oil paint characteristics was established. LDP melt was found to form a solid block on solidifying. Kerosene was added to the hot (1150C) LDP melt, which on cooling resulted into a liquid mixture with solid suspensions. On adding kerosene to hot (210[degrees]C) LDP melt, a solution without solid suspensions was produced. However, on application of LDP : kerosene mixture on glass surfaces the dry film developed cracks and peeled off easily when rubbed with a finger. To overcome this drawback, long drying oil alkyd resin was added to the mixture to stop the cracking of the film. The resulting an aqueous mixture whose application properties, condition in container, resistance to washing and resistance to accelerated weathering met the requirements for semi-gloss solvent borne paints for interior and exterior use according to Kenya specifications.

This research has provided a method for converting low density polyethylene (LDP) into anaqueous product which can be further developed into a semi-gloss solvent borne paint for interior and exterior use. In doing this, LDP materials will be removed from the waste stream thus addressing both human and environmental problems associated with them. It is recommended that further research should be conducted to develop a method for further improving the aqueous product into a standard interior and exterior semi-gloss solvent borne paint.


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Benson H.K Karanja (1) *, Isaac K. Inoti (2), Jopseph M. Keriko (3) and George T. Thiong'o (4)

(1) Institute of Energy and Environmental Technology, Jomo Kenyatta University of Agriculture and Technology (JKUAT), P.O. Box 4167-01002, Thika, Kenya (2) Department of Bio-Mechanical and Environmental Engineering, JKUAT (3) Department of Chemistry, JKUAT (4) Department of Chemistry, JKUAT * Corresponding Author Email:
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Author:Karanja, Benson H.K.; Inoti, Isaac K.; Keriko, Jopseph M.; Thiongo, George T.
Publication:International Journal of Applied Environmental Sciences
Geographic Code:6KENY
Date:May 1, 2012
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