**2. Experimental study**

144 The Development and Application of Microwave Heating

dechlorinated to synthesize polyene.[7]

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

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.

#### **2.1. Sample and reagent**

The materials used included flexible PVC with the composition indicated in Table 1. The weight ratio of dioctyl phthalate (DOP) plasticizer was roughly 30%, compared to a weight ratio of roughly 60% for PVC polymer. Other components included the oil added upon molding and UV stabilizers. We confirmed that the PVC polymer contained 35.7% of chlorine according to elementary analysis. We also used NaOH (Merck GR99%) diluted in distilled water as the NaOH solution for extraction and removal treatment in this study. Ethylene glycol was used without adding anything.

#### **2.2. Reactor**

A general purpose microwave heater (Milestone General) was used for the reaction experiments.[18] The heater had a fixed microwave frequency of 2.45 GHz, a maximum output of 1kW, a maximum usable temperature of 240°C, a maximum usable pressure of 3.4MPa, with a 100-ml reactor vessel. The reactor vessel was made of tetrafluoroethylene perfluoroalkylvinylether (PFA) copolymer, and the outer tube was made of polyether ether ketone (PEEK). In the container was also a magnetic stirrer so that the contents could be stirred. The mechanism also came with a temperature sensor to measure the temperature of the solution in the container. The temperature sensor measurement was also fed back to control microwave output. The inside of the device, including the reactor vessel, was not easily heated by microwaves, and both the reactor vessel and outer tube protecting the reactor vessel were made of materials that easily transmit microwaves. To ensure even heating distribution, the reactor vessel was also placed on a rotary stand. When heating was completed, the inside of the device and reactor vessels were cooled by a built-in fan. Conditions such as the reaction temperature and heating time were controlled using the exclusive control settings. The temperature elevation time, hold temperature, and temperature hold time can be input into the oven in advance, and the oven operates automatically.
