Environmental requirements for testing of the hott

2022-09-19
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Environmental requirements for testing of flexible packaging materials

1 test environment

the test environment mentioned in this paper refers to the laboratory environment generally used for testing the physical properties of flexible packaging materials (films, etc.) samples, excluding the special environment used for some special tests, materials, or simulating a specific climatic condition. Generally speaking, there are mainly the following three indicators: ambient temperature, ambient humidity, and air circulation flow rate in the laboratory. Among them, the temperature and humidity of the test environment will have a significant impact on the test results of the physical properties of soft packaging polymers, so it needs to be controlled

2 GB/T

GB/t2918-1998 "standard environment for condition adjustment and testing of plastic samples" is the most widely used standard related to the test environment in China. It adopts the international standard is0291:1997 "plastics - standard environment for condition adjustment and testing", and puts forward the specifications for condition adjustment and testing of various plastics and various samples under constant environmental conditions equivalent to the average environmental conditions of the laboratory. The purpose of state adjustment of the sample is to realize the reproduction of the equilibrium state of temperature and/or moisture content between the sample and the state adjustment environment or temperature

note: the values in Table 1 are applicable to general altitude with atmospheric pressure between 86kpa and 106kpa and air circulation rate ≤ 1m/s

if humidity has no effect on the measured performance or its effect is negligible, it is not necessary to control the relative humidity. The corresponding two environments are called "temperature 23" and "temperature 27"

condition adjustment week, therefore, it is necessary to use testing equipment to test whether the external wall insulation material is qualified. The qualification period should be specified in the relevant standards of the material. When the state adjustment cycle is not specified in the corresponding standards, the following cycles should be used:

a) for standard environments 23/50 and 27/65, not less than 88H

b) for room temperature of 18 ~ 28 ℃, not less than 4H

unless otherwise specified, the specimen after condition adjustment shall be tested under the same environment or temperature as the condition adjustment. In any case, the test should be carried out immediately after taking the sample out of the condition conditioning environment

3 effect of temperature and humidity changes on the properties of polymers

according to the order of polymer arrangement, solid polymer can be divided into crystalline, amorphous and oriented states. The vast majority of crystalline polymers are semi crystalline polymers, with both crystalline and amorphous parts. The difference is that the degree of crystallization is different

the longer the polymer molecular chain is, the more its conformation is. When the temperature rises, the faster the conformation of the molecular chain changes due to thermal movement, and the cohesion of the polymer decreases. Some properties of polymers (such as mechanical properties, electrical properties, barrier properties) are largely related to temperature, and these correlations are particularly prominent when polymers undergo aggregation state transition

for example, for the test of tensile properties in mechanical properties, the stress-strain curve of thermoplastic resin (an important index of mechanical properties of polymer materials) will transfer from hard brittleness to viscoelasticity with the increase of temperature. The elongation of crystalline polymers varies greatly with temperature in the range of 1% - 1000%, and the tensile strength changes within 10 times. For plastics with low water absorption, the influence of humidity on the test is not significant; For materials with strong water absorption like polyamide, the stress-strain curve changes significantly due to water absorption. These water molecules act as polyamide molecular plasticizer and soften the material

another example is that the impact property test of materials depends on temperature. In low temperature, the impact strength is urgent. We should pay special attention to this sharp reduction when choosing equipment; On the contrary, the impact strength is significantly improved at higher test temperature; The impact strength decreases with the decrease of temperature. Humidity also affects the impact strength of materials. For example, when the humidity is high, the impact strength of nylon plastics increases greatly, and the impact strength is very low in the absolutely dry state

the temperature and humidity control of the test environment has a significant impact on the barrier test of the sample, especially the temperature has the most significant impact on the barrier test. Please refer to the article "the impact of temperature change on the barrier of materials" at the Languang Laboratory Forum on February 21st, 2005. Generally speaking, the influence of humidity on the property of "road determines fate" of materials is not as obvious as temperature fluctuation (except for hygroscopic materials), so there are no excessive requirements for environmental humidity. Generally, it is only necessary to control the temperature of the test environment

4 current situation of domestic laboratory environment

the testing institutions of soft packaging materials in China mainly include national testing institutions, teaching and research institutions, various quality inspection departments, etc., but the laboratory environmental conditions are uneven, some of which can meet the requirements of accurate temperature control, and some of which are slightly worse

there are two common methods of temperature control: using a full set of Laboratory environmental control system (very few domestic laboratories use this control system), and using air conditioning to control temperature (common methods of temperature control). The former has a very good temperature control effect, while the latter is worse. Especially in spring and autumn every year, the indoor and outdoor temperature difference is small, so it is difficult to control the temperature. Temperature fluctuation will have a significant impact on the detection of physical properties of soft packaging materials. If the temperature control is not good, the test data of the same index is prone to large fluctuations, which usually shows poor data stability. Therefore, it is meaningless to evaluate the accuracy and data repeatability of a certain detection equipment in this test environment. If the wall thickness of the laboratory is large and the temperature fluctuation of the location is relatively small (such as a shady room), the ideal temperature control effect can be achieved through air conditioning

5 necessity of test environment

according to the requirements of the national standard gb/t 2918, the testing of plastics in the current global pattern of plastic machines needs to be carried out under the specified standard environment. If the physical properties of materials are tested in a non-standard environment, the test results obtained must be different from those in a standard environment, so the tests obtained under different test conditions are not comparable. On the one hand, the standard environment is used to regulate the test environment, on the other hand, it is to make the test results issued by various testing institutions comparable. Therefore, it is necessary to realize the accurate control of the test environment

however, in order to realize the control of the test environment, it is not necessary to start with the control of the laboratory environment. Choosing equipment with temperature and humidity self-control function is also a very effective method. For example, vac-v1 gas permeameter, tsy-t1, T2 and T3 moisture permeability testers launched by Labthink Languang have the function of automatic temperature control at room temperature ~50 ℃

source: Jinan Languang Electromechanical Technology Co., Ltd

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