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GB/T 24128-2009 English PDF (GBT24128-2009)

GB/T 24128-2009 English PDF (GBT24128-2009)

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GB/T 24128-2009: Method for testing resistance of plastics to mold

This Standard specifies the anti-mold performance test of plastic materials and their products such as tubes, rods, sheets and films. This Standard is applicable to the determination of the effects of changes in the optical, mechanical and electrical properties of plastics caused by mold growth. This Standard does not involve relevant safety issues. Before using this Standard, the user shall formulate appropriate safety and health regulations in advance, and determine the scope of application and limitation.
GB/T 24128-2009
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 83.080
G 31
Method for Testing Resistance of Plastics to Mold
ISSUED ON: JUNE 15, 2009
IMPLEMENTED ON: FEBRUARY 01, 2010
Issued by: General Administration of Quality Supervision, Inspection and Quarantine;
Standardization Administration of the PEOPLE Republic of China.
Replaced
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative References ... 5
3 Overview ... 5
4 Usage and Significance ... 5
5 Apparatus ... 6
6 Reagents and Materials ... 7
7 Spore Viability Test ... 10
8 Test Sample ... 10
9 Test Procedures ... 11
10 Test Report ... 12
11 Uncertainty ... 12
Appendix A (Informative) Technical Differences and Causes between this Standard and ASTM G21:1996(2002) ... 13
Bibliography ... 15
Method for Testing Resistance of Plastics to Mold
1 Scope
1.1 This Standard specifies the anti-mold performance test of plastic materials and their products such as tubes, rods, sheets and films. This Standard is applicable to the determination of the effects of changes in the optical, mechanical and electrical properties of plastics caused by mold growth.
1.2 This Standard does not involve relevant safety issues. Before using this Standard, the user shall formulate appropriate safety and health regulations in advance, and determine the scope of application and limitation.
2 Normative References
The provisions in following documents become the provisions of this Standard through reference in this Standard. For dated references, the subsequent amendments (excluding corrigendum) or revisions do not apply to this Standard, however, parties who reach an agreement based on this Standard are encouraged to study if the latest versions of these documents are applicable. For undated references, the latest edition of the referenced document applies.
GB/T 2918-1998 Plastics - Standard Atmospheres for Conditioning and Testing (idt ISO 291:1997)
3 Overview
This Standard includes the following procedures: select appropriate samples; inoculate the samples with appropriate molds; expose the inoculated samples to an environment suitable for mold growth, detect and evaluate the growth level of molds; take out samples, conduct the subsequent test after the conditioning.
NOTE: Since the testing process involves the use of mold, it is recommended that the mold and inoculated samples be used by personnel trained in microbiology.
4 Usage and Significance
4.1 The polymer component in the plastic does not have the carbon source required for the growth of mold, and has an inhibitory effect on the growth of mold. Other components in plastics such as plasticizers, fiber fillers, lubricants, stabilizers and colorants are often the main cause of mold infection. In the environment where the material is most susceptible to mold infection (temperature 2??? ~ 38??? and relative humidity 60% ~ 100%), it is very important to verify its ability to resist mold infection.
4.2 The expected impacts are as follows:
a) After the plastic and its products are infected by mold, it can be observed that the surface of the plastic and its products is corroded, faded and the light transmittance is reduced. b) Removal of plasticizers, modifiers and lubricants from the material shall result in an increase in the modulus (rigidity) of the plastic, changes in weight, dimensions and other physical properties, as well as decrease of electrical properties such as insulating properties, dielectric constant, power factor and dielectric strength.
4.3 Generally, the change of electrical properties mainly depends on the growth of mold on the plastic surface and the change of humidity and pH value caused by the secretion of metabolites by the mold; and the predominant growth of mold caused by the uneven distribution of plasticizers, lubricants and other processing aids can also cause the change of electrical properties. Ion-conducting channels are often left behind when mold attacks the material. Significant physical changes can be observed in film products, because of the large specific surface area of the film, when surface nutrients such as plasticizers and lubricants are utilized by molds, they can continue to migrate from the interior of the film.
4.4 The mold has a high probability of local growth or inhibition on the surface of the material, resulting in low reproducibility of the test results. In order to ensure the reliability of the evaluation results, the maximum degree of damage observed should be taken as the test result. 4.5 After being subjected to conditions such as water spraying, natural aging and heat treatment, the anti-mold properties of the sample shall be affected, and this Standard does not include the test of these effects.
5 Apparatus
5.1 Main apparatus
5.1.1 Constant temperature and humidity incubator
The temperature can be maintained at 28 ??? ?? 2 ???, and the relative humidity can be maintained at 90% ?? 5%.
5.1.2 High pressure steam sterilizer
The temperature is set at 105 ??? ~ 126 ???, and the pressure reaches 0.145 MPa ~ 0.165 MPa. 5.1.3 Dry heat sterilizer
6.2 Water
Unless otherwise specified, the used water shall be distilled water or water of equivalent purity. 6.3 Nutrient salt medium (for culturing samples)
6.3.1 Components
Potassium dihydrogen phosphate (KH2PO4): 0.7g;
Magnesium sulfate (MgSO4 ?€? 7H2O): 0.7g;
Ammonium nitrate (NH4NO3): 1.0g;
Sodium chloride (NaCl): 0.005g;
Ferrous sulfate (FeSO4 ?€? 7H2O): 0.002g;
Zinc sulfate (ZnSO4 ?€? 7H2O): 0.002g;
Manganous sulfate (MnSO4 ?€? H2O): 0.001g;
Dipotassium hydrogen phosphate (K2HPO4): 0.7g;
Agar: 15.0g;
Water: 1000mL.
6.3.2 Preparation
Heat and dissolve the components in 6.3.1; adjust the pH to 6.0~6.5 by 0.01 mol ?€? L-1 NaOH solution; pack in aliquots; and autoclave at 121 ??C for 20 min.
6.3.3 Prepare sufficient medium for the test needs.
6.4 Nutrient salt solution (for diluting spore solution)
The nutrient salt solution is the same as the other components in 6.3.1, except that the agar is not added. Heat to dissolve; adjust the pH to 6.0~6.5 by 0.01 mol ?€? L-1 NaOH solution; pack in aliquots; and autoclave at 121 ??C for 20 min.
6.5 Potato-sucrose medium (for mold cultivation)
6.5.1 Components
Potato: 200g;
Sucrose: 20g;
6.6.5 Centrifuge the filtered spore suspension at a speed of 4000 r/min under sterile conditions; remove the supernatant; resuspend the spore precipitate with 50 mL of sterile water and re- centrifuge.
6.6.6 Wash the spores three times with the above method; and dilute the spore precipitate after washing and centrifugation by a nutrient salt solution; so that the suspension contains 8 ?? 105 cfu/mL ~ 1.2 ?? 106 cfu/mL of spores (calculated by a counter).
6.6.7 Repeat the above operations for each mold used in the test; and mix them in equal amounts to obtain a mixed spore suspension.
6.6.8 A fresh spore suspension shall be prepared for each test, or the spore suspension shall be stored at 3??C ~ 10??C for no more than 4 days.
7 Spore Viability Test
Cut 3 pieces of filter paper into squares with a side length of 25mm; and after sterilization, place the filter paper flat in a plate containing nutrient salt medium; and then use a sterilized sprayer to spread the mixed spore suspension (6.6) evenly to the surface of the filter paper; so the mixed spore suspension wet the entire surface of the filter paper (spray pressure ???110kPa); and the inoculated plate was placed at conditions of 28 ??? ~ 30 ???, and the relative humidity no lower than 85%, then test it after culturing to 14 days. There shall be obvious mold growth on all 3 pieces of filter paper. If there is no mold growth, test again. 8 Test Sample
8.1 The sample can be a square piece of 50mm ?? 50mm, or a round piece with a diameter of 50mm, or a piece (rod or tube) no less than 76mm long cut from the material to be tested. The whole product material or a part of it can be used as a test sample. Sample test results are limited to the evaluation of changes in physical properties such as appearance, bacterial growth density, light reflection or transmission, or hardness.
8.2 The film material is tested with a size of 50mm ?? 25mm as a sample. 8.3 For visual evaluation, three parallel samples shall be inoculated. If the front and back sides of the samples are different, both the front and the back sides of the samples shall be tested. NOTE: To design a test procedure for the detection of quantitative changes during and after exposure to mold, a sufficient amount of sample is required to determine a valid data assessment of the initial performance of the sample. If five parallel samples are required to determine the tensile strength of a film material, then the same number of samples shall be selected for each exposure cycle. The expected values of the material's physical properties are different at each stage of mold action; and the value of maximum degradation is the most effective (4.4).
not covering the entire sample, shall be rated as Level-2.
9.4 Influence of physical properties, optical properties and electrical properties The mold on the sample was washed off; immerse in mercuric chloride solution (volume ratio 1:1000) for 5 min; then washed with tap water; and dried at room temperature for 8 h ~ 12 h. According to the provisions in GB/T 2918-1998, the conditioning is carried out under the test conditions of temperature 23??? ?? 1??? and relative humidity 50% ?? 5%. The conditioning of the control sample is also carried out according to the provisions in GB/T 2918-1998. NOTE: For tests of certain electrical properties, such as insulation and arc resistance, the samples can be tested without cleaning and in a wet condition. Its test value is affected by surface mold growth and its humidity.
10 Test Report
The test report shall include the following:
a) The used mold;
b) The culture time (if the test is terminated in advance, indicate it in the report); c) Level of visible mold growth (see 9.3);
d) List the changes of physical, optical and electrical properties as the incubation time; and give the average and maximum values of the observed number of samples and their related properties.
11 Uncertainty
The uncertainty of the test method has not been obtained because interlaboratory test data are not available. A statement of uncertainty shall be given in the next revision when interlaboratory data are available.

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