250
P. Nag et al.
1 Introduction
Environmental pollution is one of the most serious problems that the ecosystem is
facing today. Increased use of plastic in every fields of life is nowadays considered
as the most dangerous threat to the environment. Accumulation of waste plastic on
the land is greater and more concentrated than that in the water. As per the estimate
by Central Pollution Control Board (CPCB) the plastic consumption in India is 8
million tons per annum and about 5.7 million tons of plastic is converted into waste
annually (Rathi 2006; Chakrabarty et al. 1995).
These waste plastics are generally littered into soil and water bodies and cause
serious damage to the environment. Due to the non-biodegradable and impervious
nature of plastics, if disposed in the soil, they create resistance to the recharging of
groundwater aquifers in addition to polluting soil. Traditional methods for plastic
waste handling are often creating new environmental difficulties. Incineration is one
conventional way of treating plastic wastes but complete and incomplete combustion
of waste plastics generates hazardous greenhouse gases, carcinogenic compounds,
and acidic gases along with soot and ash. These combustion products are toxic,
mutagenic, and endocrine disruptors (Lee et al. 1995). With the excessive use of
plastics and increasing need for efficient plastic waste disposal, the demand for
developing material which does not burden the environment significantly has been
increased in the recent years. Many scientists advocate for the development of
biodegradable plastics. But recently several disadvantages of biodegradable plastics are noticed; moreover, they are still not economical and widely available. So
the need for invention of easily degradable plastic material is a demand of the day.
Research is going on throughout the world to develop synthetic plastic films that can
undergo degradation by several natural conditions like sunlight, ambient temperature,
humidity, and microorganisms. According to different studies, soil microbial populations play crucial role in biodegradation of plastics. The polymer is first converted
to its monomers during degradation then the monomers are absorbed into microbial cells and biodegraded (Goldberg 1995). The characteristics of polymer such as
mobility, crystallinity, molecular weight, functional groups, and substituents present
in its structure, and plasticizers or additives, all play significant roles in its degradation (Artham and Doble 2008; Gu et al. 2000). Campos et al. (2011) showed that
plastic-blended films were achieved significant biodegradation in a very short incubation time. Ishigaki et al. (1999) have studied the mechanism of biodegradation of
the blended film. It is also true that light energy generally degrades plastic. Solar
photodegradation of plastics can be enhanced using semiconductor photocatalysis
(Cho and Choi 2001; Zhang et al. 2004). Cho and Choi (2001) reported 27% loss in
weight for PVC-TiO 2 film (1.5 wt% TiO 2 ) under 200 W mercury lamp (1.5 mW/cm
2
between 300 and 400 nm wavelength) after 300 h of exposure. On the other hand,
Zhang et al. (2004) observed about 50% weight loss with TiO 2 -PVC film under a
250 W lamp (2.0 mW/cm
2 ) in 250 h. Chakrabarti et al. (Chakrabarti and Dutta 2008;
Sil and Chakrabarti 2010; Chakrabarti et al. 2011) reported photocatalytic degradation of polymer-ZnO composite materials. In another study, they showed 12.29%
P. Nag et al.
1 Introduction
Environmental pollution is one of the most serious problems that the ecosystem is
facing today. Increased use of plastic in every fields of life is nowadays considered
as the most dangerous threat to the environment. Accumulation of waste plastic on
the land is greater and more concentrated than that in the water. As per the estimate
by Central Pollution Control Board (CPCB) the plastic consumption in India is 8
million tons per annum and about 5.7 million tons of plastic is converted into waste
annually (Rathi 2006; Chakrabarty et al. 1995).
These waste plastics are generally littered into soil and water bodies and cause
serious damage to the environment. Due to the non-biodegradable and impervious
nature of plastics, if disposed in the soil, they create resistance to the recharging of
groundwater aquifers in addition to polluting soil. Traditional methods for plastic
waste handling are often creating new environmental difficulties. Incineration is one
conventional way of treating plastic wastes but complete and incomplete combustion
of waste plastics generates hazardous greenhouse gases, carcinogenic compounds,
and acidic gases along with soot and ash. These combustion products are toxic,
mutagenic, and endocrine disruptors (Lee et al. 1995). With the excessive use of
plastics and increasing need for efficient plastic waste disposal, the demand for
developing material which does not burden the environment significantly has been
increased in the recent years. Many scientists advocate for the development of
biodegradable plastics. But recently several disadvantages of biodegradable plastics are noticed; moreover, they are still not economical and widely available. So
the need for invention of easily degradable plastic material is a demand of the day.
Research is going on throughout the world to develop synthetic plastic films that can
undergo degradation by several natural conditions like sunlight, ambient temperature,
humidity, and microorganisms. According to different studies, soil microbial populations play crucial role in biodegradation of plastics. The polymer is first converted
to its monomers during degradation then the monomers are absorbed into microbial cells and biodegraded (Goldberg 1995). The characteristics of polymer such as
mobility, crystallinity, molecular weight, functional groups, and substituents present
in its structure, and plasticizers or additives, all play significant roles in its degradation (Artham and Doble 2008; Gu et al. 2000). Campos et al. (2011) showed that
plastic-blended films were achieved significant biodegradation in a very short incubation time. Ishigaki et al. (1999) have studied the mechanism of biodegradation of
the blended film. It is also true that light energy generally degrades plastic. Solar
photodegradation of plastics can be enhanced using semiconductor photocatalysis
(Cho and Choi 2001; Zhang et al. 2004). Cho and Choi (2001) reported 27% loss in
weight for PVC-TiO 2 film (1.5 wt% TiO 2 ) under 200 W mercury lamp (1.5 mW/cm
2
between 300 and 400 nm wavelength) after 300 h of exposure. On the other hand,
Zhang et al. (2004) observed about 50% weight loss with TiO 2 -PVC film under a
250 W lamp (2.0 mW/cm
2 ) in 250 h. Chakrabarti et al. (Chakrabarti and Dutta 2008;
Sil and Chakrabarti 2010; Chakrabarti et al. 2011) reported photocatalytic degradation of polymer-ZnO composite materials. In another study, they showed 12.29%