Determination of residual non-polyester substances in recycled polyester bottle flakes

Abstract

The invention belongs to the technical field of analytical chemistry, and specifically relates to a method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes. The method performs detection through the steps of sample weighing, pretreatment, sample constant weight, filtration and washing, secondary constant weight, and improves the weighing bottle used for detection, thereby greatly improving the detection efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of analytical chemistry, and in particular relates to a method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes. Background Art

[0002] Polyester is a general term for polymers obtained by condensation of polyols and polyacids. It mainly refers to polyethylene terephthalate (PET), and also customarily includes linear thermoplastic resins such as polybutylene terephthalate (PBT) and polyarylates. It is a type of engineering plastic with excellent performance and wide application. It can also be made into polyester fibers and polyester films.

[0003] Recycled polyester bottle flakes mainly refer to various forms of discarded PET packaging bottles, which are made into shredded PET flakes through sorting, cleaning, label removal, crushing, drying and other processes. Since my country's recycled polyester fiber industry accounts for about 85% of the global total, domestic raw materials are far from meeting demand, so a large amount of recycled polyester bottle flakes must be imported from abroad.

[0004] Recycled polyester bottle flakes belong to PET crushed materials and scraps (customs code 3915901000). According to the "Reply of the Ministry of Ecology and Environment of the People's Republic of China on the Identification of the Properties of Solid Waste of Imported Recycled Polyester (PET) Bottle Flakes", imported high-purity recycled polyester (PET) bottle flakes have been sorted, crushed and cleaned abroad, and meet the A, B and C performance and index requirements of the "Textile Industry Standard of the People's Republic of China Recycled Polyester (PET) Bottle Flakes (FZ / T 51008-2014)". After import, they can be directly processed and utilized to replace virgin materials, and are not regulated as solid waste, that is, they are imported as ordinary goods.

[0005] In the application, it was found that the operating steps of the "Textile Industry Standard of the People's Republic of China Recycled Polyester (PET) Bottle Flakes (FZ / T 51008-2014)" were vague, and the operating conditions were difficult to control or even difficult to achieve, resulting in the experimenter's subjective factors having a greater impact on the experimental results, especially the "non-polyester (PET) substance residue" item. The specific operation process is as follows:

[0006] 1. Weigh about 2000g of sample and spread it evenly in a dry and clean sample pan of known mass;

[0007] 2. Place the sample pan in a drying oven that has been pre-aired and heated to (105±5)℃, dry for 1.5 hours under continuous air blowing conditions, take out the sample pan from the drying oven, and weigh it immediately (accurate to 0.001g);

[0008] 3. Put the sample disc into the drying oven and heat it. Take out the sample disc from the drying oven after drying for 30 minutes and weigh it immediately (accurate to 0.1g) until the difference between the two mass of the sample does not exceed 1g;

[0009] 4. Weigh (300.00±5.00)g of bottle flakes (m0) from the dried sample pan and put them into a volumetric flask. Use a measuring cylinder to measure 1000mL of acetone and slowly inject it into the volumetric flask and cover the bottle with a stopper. Then, lift the volumetric flask and shake it evenly (for at least 1min), then let it stand for 15min. Pour out the acetone cleaning solution in the volumetric flask, being careful not to pour out the bottle flakes.

[0010] 5. Add about 1000mL of tap water to the volumetric flask to clean the bottle pieces. After cleaning, use about 500mL of distilled water to clean the bottle pieces, and then filter out all the bottle pieces;

[0011] 6. Put it in the drying oven that has been pre-aired and heated to (105±5)℃ again, and dry it for 1.5 hours under continuous air blowing. Take out the sample disk from the drying oven and weigh it immediately (accurate to 0.001g), then put the sample disk in the drying oven again and heat it. Take out the sample disk from the drying oven after every 30 minutes of drying and weigh it immediately (accurate to 0.001g), until the difference in the mass of the sample does not exceed 1g;

[0012] 7. Take the minimum mass value of the sample as the mass of the sample after drying (m1) and record it.

[0013] However, the above method still has a lot of defects:

[0014] (1) In step 1-2, it is currently impossible to obtain a balance that can simultaneously meet the requirements of "weighing a sample of 2000 g and being accurate to 0.001 g";

[0015] (2) In step 3, if the sample is not cooled, it is impossible to "take out the sample plate from the drying oven, accurate to 0.1g";

[0016] (3) The volumetric flask in step 4 is not suitable as a cleaning container and is inconvenient to operate;

[0017] (4) The accuracy of step 4 “weighing the sample (300.00±5.00) g” is not enough, which affects the final result judgment, because the deviation of 0.01 g relative to the sample weight of 300 g is 33.33 mg / kg, while the limit requirement for Class C in the standard is only “<50 mg / kg”;

[0018] (5) In step 6, if the sample is not cooled, it is impossible to "remove the sample plate from the drying oven with an accuracy of 0.001g";

[0019] (6) Step 6 requires that “the difference between the two masses does not exceed 1 g”. This condition is too broad and seriously affects the final result. This is because a deviation of 1 g is 3333 mg / kg relative to a sample weight of 300 g, while the standard limit requirement for Class C is “<50 mg / kg”. Summary of the invention

[0020] In view of the above problems, the present invention provides a method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes, which is simple to operate, easy to implement and has accurate detection results.

[0021] In order to achieve the above object, the present invention adopts the following technical solutions:

[0022] The method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes comprises the following steps:

[0023] (1) Weighing the sample: Weigh the sample, pour it into the sieve and vibrate it, discard the sieved material to obtain the sieved sample;

[0024] (2) Pretreatment: The weighing bottle including the weighing bottle body and the weighing bottle cap and the filter paper are washed with acetone and then dried. The dried filter paper is then placed in the weighing bottle body and covered with the weighing bottle cap. After being taken out and cooled, the weighing bottle is weighed and the mass is recorded as m0;

[0025] (3) Constant weight of sample: Weigh the sieved sample and spread it on the sample tray, dry the sample tray with the sieved sample, the weighing bottle, the weighing bottle cap, and the filter paper, turn the sieved sample over, transfer all the sieved sample into the weighing bottle, continue drying, then put the filter paper into the weighing bottle and cover it with the weighing bottle cap, take it out and cool it, weigh the weighing bottle, record the mass as m1, then open the weighing bottle cap to dry it, close the weighing bottle cap, take it out and cool it, weigh the weighing bottle, record the mass as m1';

[0026] (4) Filtration and washing: slowly pour acetone into the weighing bottle, shake the weighing bottle and let it stand, replace the weighing bottle cap with a hole, stick the filter paper on the funnel, and then filter the acetone washing liquid. After washing the sample in the weighing bottle with water, transfer it to the sample tray and spread it out;

[0027] (5) Second constant weight: Dry the sample pan with the sample in step (4) together with the weighing bottle, weighing bottle cap and filter paper, and turn the sample over to transfer the entire sample into the weighing bottle. Continue drying. Then put the filter paper into the weighing bottle and cover it with the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m2. Open the weighing bottle cap to dry it. Close the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m2'.

[0028] The principle of the detection method of the present invention is the same as the national standard method, both of which use acetone to remove the non-polyester (PET) material residues on the sample surface, and use the mass change before and after to obtain the residual amount. Although the principle is the same, there are large differences in the implementation methods. As the defects listed in the background technology of the present invention, it is difficult for the national standard method to accurately obtain the test results. The present invention reduces the sample weighing amount of the sample to ensure that the sample is weighed once, avoiding the excessive sample amount in the national standard and the increase of errors in multiple weighings. Pretreatment is used to avoid substances that may be attached to instruments such as weighing bottles and filter paper and are soluble in acetone, further ensuring the accuracy of the test results. The present invention can complete the entire operation process through an aluminum weighing bottle, greatly simplifying the operating steps of the analytical experiment, saving manpower and material resources, and accelerating the detection of samples.

[0029] Preferably, the amount of the sample in step (1) is 1000 g ± 10 g, and the amount of the sieved sample in step (3) is 300 g ± 5 g.

[0030] Preferably, the weighing in steps (1) and (3) is performed on an electronic balance, the graduation value of the electronic balance is 0.1 g, and the aperture of the sieve is 0.833 mm. Controlling the size of the sample is helpful to reduce the influence on the result caused by the loss of acetone and water in the powdered polyester sample.

[0031] Preferably, the drying treatments in steps (2), (3) and (5) are all carried out in a preheated air drying oven at a preheating temperature of 100-110° C., and the weighing of the weighing bottle is all carried out on an analytical balance with a graduation value of 0.001 g.

[0032] Preferably, the weighing bottle is an aluminum weighing bottle. The capacity of the weighing bottle is ≥1000 mL. The present invention adopts a specific aluminum weighing bottle to replace a conventional container, which not only greatly increases the space capacity, but also the weight stability of the aluminum material is better than that of the glass material. It is the good quality stability that can reduce the number of blast drying and thus save detection time. The bottle cap of the aluminum weighing bottle is specially made into a closed weighing bottle cap and a weighing bottle cap with a hole, and the aperture of the weighing bottle cap with a hole is smaller than the particle size of the bottle flakes.

[0033] Preferably, the drying time in steps (3) and (5) is 2.0-3.0 hours, and the interval between turning the sample is 0.5 hours. The method of steps (3) and (5) does not change much, but the control of parameters needs to be more stringent. First, the drying time cannot be less than 2.0 hours to minimize the impact of moisture on the test results. Secondly, the time the samples of the two steps are placed in the dryer should be kept consistent as much as possible to minimize errors.

[0034] Preferably, in steps (3) and (5), the differences between the masses m1 and m1', and between m2 and m2' are calculated, Δm1 = |m1-m1'|, Δm2 = |m2-m2'|.

[0035] Further preferably, when Δm1 and / or Δm2>0.01g, the operation is repeated until Δm1 and Δm2≤0.01g. Since the error of 0.01g is 33.3mg / kg relative to the sample weight of 300g, and the prescribed limit is 50mg / kg, the error generated after exceeding this difference is too large.

[0036] Preferably, step (4) can also be transferred to a glass bottle for operation, specifically: transfer the sample to the glass bottle, slowly pour acetone, cover the glass bottle cap, shake the glass bottle and let it stand, attach filter paper to the funnel, filter the acetone washing solution, and then transfer the sample in the glass bottle to the sample plate after washing. Transferring the sample will increase the complexity of the analysis experiment, but it can increase the accuracy of the analysis results and further reduce the error.

[0037] More preferably, the water washing specifically comprises: adding tap water to the weighing bottle / glass bottle to wash the sample, and then washing the sample with distilled water after washing.

[0038] More preferably, the acetone content is 950-1050 mL, the shaking time is 1-10 min, the standing time is 14-16 min, the tap water content used for washing is 950-1050 mL, and the distilled water content is 450-550 mL.

[0039] Preferably, the residual amount of the non-polyester material is calculated as follows: X = (m1-m2) × 10 6 / (m1-m0), where X (mg / kg) is the amount of non-polyester residue; m0 (g) is the total mass of the blank weighing bottle + filter paper; m1 (g) is the total mass of the sample + weighing bottle + filter paper before acetone cleaning; m2 (g) is the total mass of the sample + weighing bottle + filter paper after acetone cleaning.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] (1) The present invention avoids acetone-soluble substances that may be attached to instruments such as weighing bottles and filter papers through pretreatment, thereby further ensuring the accuracy of the test results.

[0042] (2) The present invention adopts an aluminum weighing bottle to replace the national standard glass weighing bottle, which has higher quality stability and saves detection time.

[0043] (3) The detection method of the present invention is simple to operate, easy to implement, and has accurate detection results.

[0044] (4) The present invention can complete the entire detection process through a special aluminum weighing bottle, which greatly improves the efficiency of the detection. DETAILED DESCRIPTION

[0045] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0046] Preparation before detection of the present invention:

[0047] Reagents and Materials:

[0048] Filter paper: quantitative, medium speed;

[0049] Acetone: analytical grade;

[0050] Distilled water: meets the requirements of Grade III water in GB / T 6682;

[0051] Instruments and equipment:

[0052] Blast drying oven: The temperature can be maintained at (105±5)℃;

[0053] Electronic balance: graduation value 0.1g;

[0054] Analytical balance: graduation value 0.001g;

[0055] Weighing bottle: aluminum, capacity ≥1000mL;

[0056] Measuring cylinder: 1000mL;

[0057] Screen: aperture 0.833mm;

[0058] Glass funnel;

[0059] Sample tray;

[0060] Glass bottle: with lid, capacity 2000mL.

[0061] Example 1

[0062] (1) Weighing the sample: Use an electronic balance to weigh 1000 g of the sample, pour the sample into a sieve with a pore size of 0.833 mm and vibrate it, discard the undersize to obtain the sieved sample;

[0063] (2) Pretreatment: After cleaning the weighing bottle with a capacity of ≥1000 mL, including the weighing bottle body, weighing bottle cap, weighing bottle cap with holes, and filter paper with acetone, dry them in a forced air drying oven preheated to 105°C, then put the dried filter paper into the weighing bottle body and cover it with the weighing bottle cap, take it out and cool it, weigh the weighing bottle using an analytical balance, and record the mass as m0;

[0064] (3) Constant weight of sample: Use an electronic balance to weigh 300 g of the sieved sample and spread it on the sample pan. Dry the sample pan with the sample, the weighing bottle, the weighing bottle cap, the weighing bottle cap with holes, and the filter paper in a forced air drying oven preheated to 105°C for 2.5 h. Turn the sample over every 0.5 h and transfer all the samples into the weighing bottle. Continue drying. Then put the filter paper into the weighing bottle and cover it with the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m1. Open the weighing bottle cap to dry it. Close the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m1'. Repeat the drying, cooling, and weighing for the second time until Δm1 = |m1-m1'| ≤ 0.01 g.

[0065] (4) Filtration and washing: slowly pour 1000 mL of acetone into the weighing bottle, shake the weighing bottle for 5 min and let it stand for 15 min, replace the weighing bottle cap with a hole, stick the filter paper on the funnel, and then filter the acetone solution. Wash the sample in the weighing bottle with 1000 mL of tap water and 500 mL of distilled water in turn, and then transfer it to the sample plate and spread it;

[0066] (5) Second constant weight: Dry the sample pan with the sample in step (4) together with the weighing bottle, weighing bottle cap and filter paper, and turn the sample over. After drying for 2.5 hours under continuous blowing, transfer all the samples into the weighing bottle while they are still hot and continue drying for 30 minutes. Then put the filter paper into the weighing bottle and cover it with the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m2. Open the weighing bottle cap and dry it for 30 minutes. Close the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m2'. Repeat the drying, cooling and weighing for the second time until Δm2 = |m2-m2'|≤0.01g.

[0067] (6) Calculation: According to the mass change during the test, the residual amount of non-polyester substances is calculated as follows: X = (m1-m2) × 10 6 / (m1-m0), where X (mg / kg) is the amount of non-polyester residue; m0 (g) is the total mass of the blank weighing bottle + filter paper; m1 (g) is the total mass of the sample + weighing bottle + filter paper before acetone cleaning; m2 (g) is the total mass of the sample + weighing bottle + filter paper after acetone cleaning.

[0068] Example 2

[0069] The only difference from Example 1 is that the mesh aperture of Example 2 is 1 mm.

[0070] Example 3

[0071] The only difference from Example 1 is that the mesh aperture of Example 3 is 0.5 mm.

[0072] Example 4

[0073] The only difference from Example 1 is that the interval for turning the sample in step (3) of Example 4 is 0.4h.

[0074] Example 5

[0075] The only difference from Example 1 is that the interval for turning the sample in step (3) of Example 5 is 0.6h.

[0076] Example 6

[0077] The only difference from Example 1 is that in Example 6, Δm1 is greater than 0.01 g.

[0078] Example 7

[0079] The only difference from Example 1 is that in Example 7, Δm2 is greater than 0.01 g.

[0080] Example 8

[0081] The only difference from Example 1 is that step (4) of Example 8 is carried out by transferring the mixture into a glass bottle.

[0082] Example 9

[0083] The only difference from Example 1 is that the sample weight of Example 9 is 2000 g.

[0084] Example 10

[0085] The only difference from Example 1 is that Example 10 is not cooled after drying.

[0086] Comparative Example 1

[0087] The only difference from Example 1 is that Comparative Example 1 does not perform a pretreatment operation.

[0088] Comparative Example 2

[0089] The only difference from Example 1 is that in Comparative Example 2, the same sample is tested using the national standard method of "Textile Industry Standard of the People's Republic of China Recycled Polyester (PET) Bottle Flakes (FZ / T51008-2014)" in the background technology.

[0090] The test results of Examples 1-10 and Comparative Examples 1-2 are shown in Table 1:

[0091] Table 1: Test results of Examples 1-10 and Comparative Examples 1-2

[0092]

[0093] The data in Table 1 are all for samples from the same batch.

[0094] Although the present invention has been described in detail and some specific embodiments have been cited, it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

Claims

1. A method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes, characterized in that: The method comprises the following steps: (1) Weighing samples: Weigh the sample, pour it into the sieve and vibrate it, discard the undersize to obtain the sieved sample; (2) Pretreatment: The weighing bottle, weighing bottle cap, weighing bottle cap with holes and filter paper are cleaned with acetone and dried. The dried filter paper is then placed into the weighing bottle and covered with the weighing bottle cap. After taking it out, it is cooled and the weighing bottle is weighed. The mass is recorded as m0. (3) Constant weight of sample: Weigh the sieved sample and spread it on the sample tray. Dry the sample tray with the sieved sample, the weighing bottle, the weighing bottle cap, the weighing bottle cap with holes, and the filter paper. Turn the sieved sample over and transfer all the sieved sample into the weighing bottle. Continue drying. Then put the filter paper into the weighing bottle and cover it with the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m1. Open the weighing bottle cap to dry it. Close the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m1'. (4) Filtration and washing: slowly pour acetone into the weighing bottle, shake the weighing bottle and let it stand, replace the weighing bottle cap with a hole, stick the filter paper on the funnel, and then filter the acetone washing liquid. After washing the sample in the weighing bottle with water, transfer it to the sample plate and spread it out; (5) Second constant weight: Dry the sample pan with the sample in step (4) together with the weighing bottle, weighing bottle cap and filter paper, and turn the sample over to transfer the entire sample into the weighing bottle. Continue drying. Then put the filter paper into the weighing bottle and cover it with the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m2. Open the weighing bottle cap to dry it. Close the weighing bottle cap. Take it out and cool it. Weigh the weighing bottle and record the mass as m2'. The weighing in steps (1) and (3) is performed on an electronic balance, the graduation value of the electronic balance is 0.1 g, and the aperture of the sieve is 0.833 mm; The amount of the sample in step (1) is 1000 g ± 10 g, and the amount of the sieved sample in step (3) is 300 g ± 5 g; The drying time in steps (3) and (5) is 2.0-3.0 hours, and the interval between turning the samples is 0.5 hours; The weighing bottle is an aluminum weighing bottle with a capacity of ≥1000 mL; the bottle cap of the aluminum weighing bottle is specially made to be divided into a closed weighing bottle cap and a weighing bottle cap with a hole, and the hole diameter of the weighing bottle cap with a hole is smaller than the particle diameter of the bottle flakes.

2. The method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes according to claim 1, characterized in that: The drying treatments in steps (2), (3) and (5) are all carried out in a preheated air drying oven at a preheating temperature of 100-110° C., and the weighing of the weighing bottle is all carried out on an analytical balance with a graduation value of 0.001 g.

3. The method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes according to claim 1, characterized in that: In steps (3) and (5), the differences between the masses m1 and m1', and between m2 and m2' are calculated, Δm1=|m1-m1'|, Δm2=|m2-m2'|.

4. The method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes according to claim 1 or 3, characterized in that: When Δm1 and / or Δm2>0.01g, repeat the operation until Δm1 and Δm2≤0.01g.

5. The method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes according to claim 1, characterized in that: Step (4) is to transfer the sample into a glass bottle for operation, specifically: transfer the sample into the glass bottle, slowly pour acetone into it, cover the glass bottle with a lid, shake the glass bottle and let it stand, attach filter paper to the funnel, filter the acetone solution, and then wash the sample in the glass bottle with water and transfer it to the sample plate and spread it out.

6. The method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes according to claim 1 or 5, characterized in that: The shaking time is 1-10 min, and the standing time is 14-16 min.

7. The method for determining the residual amount of non-polyester substances in recycled polyester bottle flakes according to claim 1, characterized in that: The residual amount of the non-polyester substance is calculated as follows: X=(m1-m2)×10 6 / (m1-m0), where X (mg / kg) is the residual amount of non-polyester substances; m0 (g) is the total mass of blank weighing bottle + filter paper; m1 (g) is the total mass of sample + weighing bottle + filter paper before acetone cleaning; m2 (g) is the total mass of sample + weighing bottle + filter paper after acetone cleaning.

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