**1. Introduction**

140 The Development and Application of Microwave Heating

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The amount of plastic produced in Japan was 14.65 million tons in fiscal year 2007, although this figure has fluctuated, as shown in Figure 1. As a result, the amount of plastic waste has increased to 10.05 million tons/year[1]. Most of that waste is either landfilled or incinerated.

The amount of plastic waste discharged is annually growing. Therefore, it is essential to research and develop technologies to recycle and reuse plastic waste to protect the global environment and effectively to utilize resources. In an effort to promote recycling of plastic waste. The Containers and Packaging Recycling Law was enacted in June 1995 to promote sorted collection of containers and packaging and the recycling of containers and packaging as products. To promote recycling, the scope of this law was expanded to plastic containers and packaging, instead of being limited to polyethylene terephthalate (PET) bottles. When it was amended then reenacted in April 2000, it seemed as if almost 50% of plastic waste was recycled in fiscal year 2000. However, the breakdown of effective utilization in fiscal year 2006 revealed that almost 72% was simply incinerated: [1] 40% was used for power generation, 19% was incineration to release thermal energy, 4% was used as feedstock, 9% was used as solid fuel (Figure 2). Some waste plastic from general household was also incinerated in the metropolitan area. Thus, the current situation is that most waste plastic is still either landfilled or incinerated. There is a limit to how much waste plastic that a landfill can hold, and the option of landfilling waste plastic is becoming more difficult, especially since the amount of landfill space available to bury plastic waste is annually decreasing. In fact, it has been reported that the landfills will be completely full in 14.8 years (as of end of fiscal year 2005) for general waste, and in only 7.7 years (as end of fiscal year 2005) for industrial waste. When plastic waste is landfilled, there is risk of endocrine disruptors and

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hazardous substances eluting from the waste. The specific gravity of plastic is low. Therefore, burying it poses risk of loosening the landfill ground. This makes it difficult to reuse the landfill site for other purposes. On the other hand, when waste plastic is incinerated, it tends to corrode the incinerator due to the waste plastic containing halogens such as chlorine. What is more, depending on the incineration condition, it can also generate toxic organic compounds and materials causing acid rain. Burned ash and fly ash that are buried in landfills also contain residual CaCl2 from Ca(OH)2 added to neutralize hydrogen chloride. This also increases the load on the landfill. Among waste plastic, polyvinyl chloride (PVC), whether rigid or flexible, is common because it is used in construction materials and materials for electrical wire sheathing. PVC is used as a durable and enduring product, thus, there is risk of an increase in volume discharged when buildings are renovated or rebuilt in the future.

**Figure 1.** Production and emissions of plastics

**Figure 2.** Breakdown of waste plastics to the effective use (2006)

**Figure 3.** Applications of PVC

renovated or rebuilt in the future.

**Figure 1.** Production and emissions of plastics

**Figure 2.** Breakdown of waste plastics to the effective use (2006)

Heat utilizing incineration 19%

hazardous substances eluting from the waste. The specific gravity of plastic is low. Therefore, burying it poses risk of loosening the landfill ground. This makes it difficult to reuse the landfill site for other purposes. On the other hand, when waste plastic is incinerated, it tends to corrode the incinerator due to the waste plastic containing halogens such as chlorine. What is more, depending on the incineration condition, it can also generate toxic organic compounds and materials causing acid rain. Burned ash and fly ash that are buried in landfills also contain residual CaCl2 from Ca(OH)2 added to neutralize hydrogen chloride. This also increases the load on the landfill. Among waste plastic, polyvinyl chloride (PVC), whether rigid or flexible, is common because it is used in construction materials and materials for electrical wire sheathing. PVC is used as a durable and enduring product, thus, there is risk of an increase in volume discharged when buildings are

discharge landfill Effective use

Solid fuel 9%

> Mechanical Recycling 28%

Waste power generation 40%

1990 1995 2000 2005 2010

Year

production

Feed stock recycling 4%

×104 t

**Figure 4.** Waste material coated cables

There have been many studies on PVC since 1950. However, the objectives of these studies tended to mainly focus on stabilization. Recent reports indicate that more studies have focused on recycling as a study objective. Examples include:


PVC studies are largely classified into two types: the dry method by thermal degradation and wet method. When considering the speed of temperature rise during thermal degradation of pure PVC powder, with the dry method we can get type-A crude oil with an average molecular weight of 280.[4]With the wet method, we can process flexible PVC. The plasticizer additive becomes anhydrous and then NaOH solution is added. PVC undergoes hydrolysis, and the heavy oil contents are pressurized and reheated to make light crude oil, thereby turning PVC into an oil.[5] NaOH solution can be used for dechlorination, then PVC is converted into carboxylic acids.[6] Flexible PVC film can be deplasticized and dechlorinated to synthesize polyene.[7]

We must find new methods to handle PVC waste using approaches that are not dependent on landfills and incineration. To do this, there is a need to create products with a very long usage life, as well as to promote reuse and recycling of products. If it is difficult to reuse or recycle these products, then we must support material recycling by recycling it into something else. Films are the most common form of flexible PVC,[8] as seen in the PVC product breakdown shown in Figure 3. It is most used in agricultural vinyls, as well as in packaging for agricultural fertilizers. Until recently, these items were incinerated. However, we see that tendency has changed, and that they are now often washed of adherents and residue and then reused/recycled or reused/recycled into lower quality PVC products. However, this amounts to only a fraction of the PVC waste discharged. Most of it is either incinerated or exported to Southeast Asia and China to reduce the treatment cost. The second largest waste comes from electrical wire sheathing. Roughly 1 million tons of cable sheathing is discharged as waste every year, of which 62% is PVC [9](Figure 4). About 300,000 tons, or roughly half, of this PVC undergoes material recycling and is made into flooring materials or other lower quality products, and a fraction is recycled into electrical wire sheathing materials. The reality is that the remainder is either landfilled or incinerated. The majority of PVC products discharged from different industrial fields is generally either landfilled or incinerated; however, some may be recycled. In either case, the situation is that the mode of disposal still tends to be mostly dependent on incineration. For waste that can only be incinerated, this study intends to find a way to extract and remove beforehand, thus eliminating the hydrogen chloride that would be generated upon incineration. A flexible PVC tube was used as the source of PVC in the study. We then studied whether use of external heating with a general thermal heater or internal heating with a microwave heater could promote the reaction conditions when used as the heating source for the deplasticization and dechlorination processes. It is generally known that polyvinyl chloride (PVC) is dehydrochlorinated when burnt at temperatures higher than 280°C. However, to effectively accelerate dehydrochlorination process with faster and better heat transport. Substances with low thermal conductivity are generally heated by microwaves because this procedure does not require heat transport. Thus new applications utilizing microwaves are expected to be developed in the near future. In this study, we reviewed the dehydrochlorination of flexible PVC to see if it was possible to use controllable microwave heating as a fast heating mechanism. This assumption was based on conventional wet method studies, [10-16] which indicated that substance containing Cl molecules tended to easily absorb microwaves, and materials made of flexible PVC and ethylene glycol (EG) used as a reacting solution also easily absorbed microwaves. The goal was also to accelerate dehydrochlorination by directly heating PVC molecules for early extraction of plasticizers. We similarly studied the conditions that best promote dehydrochlorination and improve reaction efficiency through an interactive effect by using substances such as EG that present good intersolubility with flexible PVC.


**Table 1.** Composition of flexible polyvinyl chloride (PVC) (wt%)
