A method for determining the thermal stability of polyvinyl chloride

Abstract

The present invention provides a method for determining the thermal stability of polyvinyl chloride, namely, a thermal decomposition temperature method. The polyvinyl chloride sample is programmed to heat in a flat-bottomed glass tube, and decomposes under heat to release hydrogen chloride gas, causing the Congo red test paper above the sample to turn blue. The square average of the starting temperature of the programmed temperature increase and the temperature when the Congo red test paper turns blue is recorded as the thermal decomposition temperature of the sample. The method of the present invention determines the thermal decomposition temperature of polyvinyl chloride, and more directly guides downstream processing users to determine processing conditions. Existing methods for characterizing the thermal stability of polyvinyl chloride are mostly indirect characterizations, and the thermal decomposition temperature cannot be given intuitively. Moreover, with the development of the polyvinyl chloride industry, some methods have limitations. In addition, compared with the thermogravimetric analysis method, the method of the present invention has a low equipment investment cost, which will help the development of the polyvinyl chloride industry.

Description

Technical Field

[0001] The invention relates to the field of thermal stability determination, and in particular to a method for determining the thermal stability of polyvinyl chloride. Background Art

[0002] Thermal stability is an important technical indicator of polyvinyl chloride (PVC) products. Currently, the methods for examining the thermal stability of PVC include whiteness method, Congo red method, color change method, hydrogen chloride water absorption method and thermogravimetric analysis method. Among them, whiteness method, Congo red method, color change method and hydrogen chloride water absorption method are all indirect methods for characterizing the thermal stability of PVC. None of them are intuitive methods for characterizing the thermal stability of PVC. The Congo red method reflects the time required for the Congo red test paper to change color at a specified heating temperature; the whiteness method is that polyvinyl chloride decomposes at high temperature and shows a decrease in whiteness. There are differences in the whiteness obtained by different samples under the same heating conditions, which reflects the difference in heat resistance. However, the products with good thermal stability of polyvinyl chloride on the market may have low whiteness, and the products with high whiteness may also have poor thermal stability. The whiteness method already has limitations. Although the thermogravimetric analysis method is intuitive, the cost of the thermogravimeter is too high.

[0003] The current market situation requires direct thermal decomposition temperature to characterize the thermal stability of PVC. Processing companies can intuitively judge the thermal stability of products based on the thermal decomposition temperature of products, thereby determining processing conditions. The method of the present invention is simple to operate, has low investment cost, good repeatability, and is more in line with actual market demand. Summary of the invention

[0004] The invention provides a method for determining the thermal stability of polyvinyl chloride - a thermal decomposition temperature method, which is used for directly characterizing the thermal stability of polyvinyl chloride.

[0005] A method for determining the thermal stability of polyvinyl chloride comprises the following steps

[0006] S1) Prepare a flat-bottomed glass tube made of borosilicate, with a length of 16±2mm, an outer diameter of 18±0.4mm, and a bottom thickness and wall thickness of 1.5±0.2mm; a thin glass tube with an inner diameter of 2-3mm and a length of 150±2mm; a stopper made of rubber, with a hole drilled in the center to allow the thin glass tube to be inserted;

[0007] S2) placing a polyvinyl chloride sample in a clean and dry flat-bottom glass tube, wherein the height of the polyvinyl chloride sample in the flat-bottom glass tube is 25±0.5 mm;

[0008] S3) Take a clean and dry thin glass tube and insert it into the stopper matched with the flat bottom glass tube, then plug the flat bottom glass tube with the stopper, roll up the Congo red test paper and insert it into the thin glass tube, so that the Congo red test paper leaks out from the bottom of the thin glass tube for a length of 8 to 10 mm;

[0009] S4) adjusting the position of the thin glass tube in the stopper so that the distance between the bottom of the Congo red test paper and the surface of the polyvinyl chloride sample is 25±1 mm;

[0010] S5) Setting a program temperature rise, heating the oil bath filled with silicone oil to a constant temperature T1 of the sample, keeping the temperature constant for 3 min, placing the assembled flat-bottomed glass tube in the oil bath filled with silicone oil, and ensuring that the surface of the polyvinyl chloride sample is not higher than the silicone oil liquid level;

[0011] S6) Raise the temperature at a rate of 0.5°C / min. When the bottom edge of the Congo red test paper turns blue, record the temperature T2 of the oil bath.

[0012] S7) Calculate the thermal decomposition temperature T of the sample according to the following formula:

[0013] Furthermore, an insulating layer is provided on the top of the oil bath for heat preservation.

[0014] Furthermore, the sample constant temperature T1 is 20±2° C. lower than the expected thermal decomposition temperature of the sample.

[0015] Expected thermal decomposition temperature of the sample: 120℃ for general-purpose polyvinyl chloride for suspension method and paste polyvinyl chloride, and 130℃ for chlorinated polyvinyl chloride. See Table 1 for recommended constant temperature.

[0016] Table 1 Recommended constant temperature for samples

[0017] Unit: ℃

[0018] Sample name Constant temperature Suspension process general purpose polyvinyl chloride 100 Polyvinyl chloride paste 100 Chlorinated polyvinyl chloride 110

[0019] The beneficial effects of the present invention are:

[0020] The method of the present invention, namely the thermal decomposition temperature method, is used to characterize the thermal stability of polyvinyl chloride, which can directly guide processing enterprises to determine processing conditions, and has low investment cost and good repeatability. DETAILED DESCRIPTION

[0021] The present invention is further described below with reference to specific embodiments, but is not limited to the contents of the description.

[0022] Example

[0023] Take a clean, dry flat-bottomed glass tube and put in the SG5 type polyvinyl chloride resin sample. The sample height is 25±0.5mm. Slightly vibrate. The sample should not be filled too tightly or stick to the wall of the glass tube. Insert the thin glass tube into the stopper, plug the glass tube with the stopper, roll up the Congo red test paper and insert it into the thin glass tube, with an exposed length of 8mm. Adjust the position of the thin glass tube in the stopper so that the distance between the bottom of the test paper and the surface of the sample is 25mm. Set the program temperature rise: Pour silicone oil into the program temperature rise oil bath until the liquid surface is (2-3) cm from the upper end of the oil bath, heat it to 100℃, record it as T1, and keep it at constant temperature for 3min. Immerse the glass tube in the oil bath, with the sample surface at the same height and not higher than the oil level, and heat it at a rate of 0.5℃ / min. When the color of the bottom of the Congo red test paper turns blue, record the temperature T2 of the oil bath. The parallel measurement results of two SG5 type polyvinyl chloride resin samples are shown in Table 2.

[0024] Table 2: Determination of thermal stability of SG5 general-purpose polyvinyl chloride resin - thermal decomposition temperature method

[0025]

[0026] The present disclosure has been described by the above-mentioned relevant embodiments, but the above-mentioned embodiments are only examples for implementing the present disclosure. It must be pointed out that the disclosed embodiments do not limit the scope of the present disclosure. On the contrary, changes and modifications made without departing from the spirit and scope of the present disclosure are all within the scope of patent protection of the present disclosure.

Claims

1. A method for determining the thermal stability of polyvinyl chloride, characterized in that: The following steps are included S1) Prepare a flat-bottomed glass tube made of borosilicate, with a length of 16±2mm, an outer diameter of 18±0.4mm, and a bottom thickness and wall thickness of 1.5±0.2mm; a thin glass tube with an inner diameter of 2-3mm and a length of 150±2mm; The stopper is made of rubber with a hole drilled in the center to insert a thin glass tube; S2) placing a polyvinyl chloride sample in a clean and dry flat-bottom glass tube, wherein the height of the polyvinyl chloride sample in the flat-bottom glass tube is 25±0.5 mm; S3) Take a clean and dry thin glass tube and insert it into the stopper matched with the flat bottom glass tube, then plug the flat bottom glass tube with the stopper, roll up the Congo red test paper and insert it into the thin glass tube, so that the Congo red test paper leaks out from the bottom of the thin glass tube for a length of 8 to 10 mm; S4) adjusting the position of the thin glass tube in the stopper so that the distance between the bottom of the Congo red test paper and the surface of the polyvinyl chloride sample is 25±1 mm; S5) Setting a program temperature rise, heating the oil bath filled with silicone oil to a constant temperature T1 of the sample, keeping the temperature constant for 3 min, placing the assembled flat-bottomed glass tube in the oil bath filled with silicone oil, and ensuring that the surface of the polyvinyl chloride sample is not higher than the silicone oil liquid level; S6) Raise the temperature at a rate of 0.5°C / min. When the bottom edge of the Congo red test paper turns blue, record the temperature T2 of the oil bath. S7) Calculate the thermal decomposition temperature T of the sample according to the following formula: The sample constant temperature T1 is 20±2°C lower than the expected thermal decomposition temperature of the sample.

2. The method for determining the thermal stability of polyvinyl chloride according to claim 1, characterized in that: An insulating layer is arranged on the top of the oil bath tank for heat preservation.

Images