CLIAMS:1. A process for preparing chlorinated polyvinyl chloride, said process comprising the following steps:

a. chlorinating polyvinyl chloride at a rate of chlorination ranging from 1.6 to 4.36 mole/hour/kg; and

b. irradiating polyvinyl chloride with ultraviolet light at a wavelength ranging from 254 to 530 nm at a predetermined radiant flux and irradiance.

2. The process of claim 1, wherein the radiant flux is 1.5 W per Kg of polyvinyl chloride.

3. The process of claim 1, wherein the irradiance is maintained at 23 mW/cm2.

4. The process of claim 1, wherein the number of photons per sec emitted is in the range of 1x1016 to 5x1020.

5. A chlorinated polyvinyl chloride having a chlorine content not less than 67 wt % chlorination prepared by the process as claimed in claim 1.

6. An apparatus for irradiation comprising a tubular assembly surrounded by series of irradiating devices.

7. The apparatus of claim 6, wherein said irradiating device emits radiation covering an angle in the range of 15 to 140°.
8. The apparatus of claim 6, wherein said apparatus consumes electricity in the range of 10 mW to 1 W. ,TagSPECI:Field

The present disclosure relates to a process for photo-irradiation of polyvinylchloride, particularly to controlled photo-irradiation of polyvinyl chloride in the presence of chlorine.

Background

Chlorinated polyvinyl chloride (CPVC) is a thermoplastic produced by chlorination of polyvinyl chloride (PVC) resin. CPVC can withstand a wider temperature range and contains more chlorine as compared to PVC. CPVC has an additional free radical chlorination process that adds chlorine to the material and increases its resiliency in terms of conveying hot materials like water. CPVC has a wide range of applications including pipes used for hot and cold water distribution in residential and industrial use, transportation of corrosive liquids, high tension cable protection pipe and the like.
CPVC is prepared by chlorination of PVC in the presence of photo-chemical reactions. Photo-chemical reaction is initiated by irradiation, irradiating photons act as reagents in stoichiometric reactions. Radiant flux (the total power emitted by source) and irradiance (the power emitted per unit area), are important parameters for light distribution in photo-reactor design. Chlorinated polymers are vulnerable to decomposition and defects are seen, mostly due to longer time of reaction. Higher Yellowness index is mostly due to double bonds, conjugation of double bolds or unsaturations.

To obtain CPVC with improved properties like thermal stability, colour and Inherent Viscosity; a specific grade of PVC is required, namely, PVC with higher porosity, higher Inherent Viscosity, higher thermal stability and lower yellowness index. However, procuring PVC with these properties results in higher running cost of the operation.

Therefore, there is felt a need for simple and economic process for preparation of CPVC, from any type of PVC.

Objects

Some of the objects of the present disclosure which at least one embodiment is adapted to provide, are described herein below:

It is an object of the present disclosure to provide a simple and economic process for photo-chlorination of a polymer using minimum radiant flux and irradiance.

It is another object of the present disclosure to provide a process for photo-chlorination of a polymer using less number of photons per second.

It is still another object of the present disclosure to provide a process for producing a chlorinated polyvinyl chloride with better thermal stability, inherent viscosity and color value.

It is yet another object of the present disclosure to obtain CPVC with improved properties including higher thermal stability, inherent viscosity and color value using PVC without any specific or special property.

Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
Summary

In accordance with the present disclosure there is provided a process for the preparation of chlorinated polyvinyl chloride, said process comprising the following steps: chlorinating polyvinyl chloride at a rate of chlorination ranging from 1.6 to 4.36 mole/hour/kg; and irradiating polyvinyl chloride with ultraviolet light at a wavelength ranging from 254 to 530 nm at a predetermined radiant flux and irradiance. The number of photons per sec emitted is in the range of 1x1016 to 5x1020.

Detailed Description

In one aspect, the present disclosure provides a process for the preparation of chlorinated polyvinyl chloride.

In one embodiment of the present disclosure the process comprises the following steps:

• chlorinating polyvinyl chloride at a rate of chlorination ranging from 1.6 to 4.36 mole/hour/kg of PVC; and

• irradiating polyvinyl chloride with ultraviolet light at a wavelength ranging from 254 to 530 nm.

A radiant flux of 1.5 W is utilized per Kg of PVC while the irradiance is maintained at 23 mW/cm2. The number of photons emitted is in the range of 1x1016/sec to 5x1020/sec. Continuous and intermittent irradiation is maintained by controlling the ratio between dark and light period. Chlorinated polyvinyl chloride prepared in accordance with the present disclosure exhibits better thermal stability and color value.
The Whiteness Index (WI) and the Yellowness Index (YI) are the two color parameters to judge CPVC product quality. Higher values of WI and lower values of YI indicate better product quality whereas lower values of WI and higher values of YI indicate poor quality of product. CPVC products with WI values higher than 84 and YI values not higher than 4.5 are compoundable.
The process for photo-chemical reaction in accordance with the present disclosure includes photo-chlorination or photo-bromination of an organic compound or a polymer at minimum radiant flux as well as at minimum irradiance. The photo-chlorination reaction is carried out with less number of photons per second and in a shorter time period. Since, the reaction is carried out over a shorter time period, the chlorinated PVC has improved thermal stability when compared with conventionally prepared chlorinated PVC.
Chlorination of polyvinyl chloride is initiated by breaking the chlorine molecular bond and creating a chlorine radical. The chlorine radical removes the hydrogen from C-H and creates a carbon radical. The carbon radical binds with chlorine and gets chlorinated. The process of creating chlorine radical and chlorinating carbon radical is repeated.
Shorter wavelength of irradiation has higher energy and thereby emits more number of photons. Energy of photon is responsible for creating initial chlorine radicals from the chlorine molecule, represented by reaction-I below.
Cl2 + h? ? 2 Cl•
Reaction-I
wherein ‘h?’ denotes photon.
Therefore, energy is required only for breaking the Cl-Cl bond. Since, chlorine is homogeneously distributed in the reaction mixture, more irradiance will create more chlorine radical. Excess chlorine radical will either recombine or create more carbon radical, which may lead to the formation of undesired byproducts. Therefore, it is preferred to keep the irradiance at a minimum level. Also, wavelength is adjusted so that the energy released is minimum or at a level required to break the bond in the chlorine molecule. Radiant flux is another factor which determines the number of photons released. More number of photons creates more radical which creates undesirable products and hence, not preferred. Therefore, it is necessary to maintain the level of irradiance, radiant flux, and the number of photons to a minimum level in order to obtain higher reaction rate.
In another aspect of the present disclosure, the apparatus for irradiation is a tubular assembly surrounded by series of small irradiating devices, emitting radiation at a wavelength of 410 nm. Each irradiating device emits radiation covering an angle in the range of 15 to 140°, preferably the covering angle is in the range of 50 to 80°. The electricity consumed by the irradiation source is in the range 10 mW to 1 W, preferably in the range of 20 to 40 mW. The operating expenses are reduced as the electricity consumption in accordance with the present disclosure is low. The apparatus takes less space as compared to conventional irradiating devices with longer wavelengths.

The process of the present disclosure is described hereinafter. Polyvinyl chloride is mixed with water to form an aqueous slurry. Nitrogen gas is purged into the slurry to remove oxygen, the slurry is simultaneously agitated. The reaction is carried out at a temperature of 70 °C. After 30 minutes the nitrogen purge is replace by chlorine purge, maintaining the same reaction conditions. When the slurry and head space is saturated with chlorine, an irradiation source at 410 nm is switched on. Start of irradiation is considered as the reaction start time. The progress of the reaction is monitored periodically by titrating proportional amount of mother liquor against 0.1N NaOH. The reaction is stopped when a titer value corresponding to 67 wt % chlorination is obtained and the irradiation is switched off. Thereafter, nitrogen is purged for 1 hour to expel free chlorine from the slurry. The slurry is filtered and the filtrate comprising the chlorinated PVC is washed and dried.

The process in accordance with the present disclosure, at a radiant flux of 1.5 W/Kg PVC, irradiance of 23 mW/cm2, chlorination of PVC using chlorine gas at a rate not less than 1.6mole/h/kg PVC, and photon emitted in the range of 1x1016 to 5x1020 resulted in a CPCV with 67 wt % chlorine content in 5 hours with yellowness index 1.37, whiteness index 96 and thermal conductivity 648 sec.
The process of the present disclosure can also be used for the chlorination of other polymers and related materials including oligomers, copolymers, composites of polymers/co-polymers/oligomers, plasticized polymers and the like.

The disclosure will now be described with reference to the following non-limiting example:

Example 1

The setup consisted of a 5 L glass vessel equipped with irradiation source at 410 nm wavelength. Each irradiating device emits radiation covering an angle of 60°. The radiant flux was maintained at 1.7 W and the irradiance was maintained at 0.1 W/cm2. The number of photons emitted per second was maintained at 1.2x1019.
630 g of PVC (K 67) having porosity of 0.23 mL/g was charged into the 5 L glass vessel and 4 L water was added to obtain an aqueous PVC slurry.

The PVC slurry was agitated at 800 rpm and simultaneously nitrogen gas was purged into the slurry. The temperature of the slurry was maintained at 70°C. After 30 minutes, nitrogen purge was stopped and chlorine was purged into the slurry maintaining the same reaction conditions. Irradiation source at 410 nm was switched on, when the slurry and head space was saturated by chlorine. Start of irradiation was considered as the reaction start time.

The reaction was monitored periodically by titrating mother liquor with 0.1 N NaOH. The reaction was stopped when a titer value corresponding to 67 wt % chlorination was obtained, and the irradiation was switched off.

After the irradiation was switched off, nitrogen gas was purged for 1 hour to expel free chlorine from the slurry.

The above slurry was filtered and the filtrate comprising CPVC was washed till a neutral pH was obtained. The wet cake obtained after the washing was dried under reduced pressure at 55 °C for 2 hours. The dried powder was further neutralized using 0.0125 N Ca(OH)2 at a concentration of 10 ml/g of CPVC for 10 minutes. The slurry formed after the neutralization step was filtered and washed with water at a concentration of 25 ml/g of CPVC. The CPVC obtained was dried at 70 °C for 3 hours.
The CPVC obtained had a chlorine content of 67.34 wt % in 4.5 hours, Whiteness Index of 85.41, Yellowness Index of 2.95, and Thermal stability by Conductivity of 504 sec.

Technical advances

- The present disclosure provides a simple and economic process for the preparation of chlorinated polyvinyl chloride at minimum radiant flux and irradiance.
- The present disclosure also provides a process for the preparation of chlorinated polyvinyl chloride using less number of photons and at a shorter time period.
- The present disclosure provides a chlorinated polyvinyl chloride with better thermal stability and improved color.

The exemplary embodiments herein quantify the benefits arising out of this disclosure and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.