RU2064678C1 - Process of determination of degree of crystallinity of materials - Google Patents

Abstract

FIELD: study of physical and structural properties of composite materials, polymers and alloys. SUBSTANCE: invention may find use for determination of structure of glass-like and composite polymer materials. Process includes heating of sample to form crystalline phase. During heating rate of thermal expansion of sample is measured with maximum and minimum values of temperature within temperature interval corresponding to formation of crystalline phase. Degree of crystallinity is determined from relation of specified rates of thermal expansion of sample. EFFECT: enhanced authenticity of process. 2 dwg

Description

 The invention relates to the study of the physical and structural properties of composite materials of polymers and alloys and can be used to determine the structure of glassy and composite polymer materials.

 The invention is intended to determine the degree of crystallinity of polymeric materials by non-destructive method.

 A known method for determining the degree of curing of materials by extraction, based on the determination of the mass of uncured resin, dissolved in acetone during extraction in a Soxhlet device.

 The disadvantage of this method [1] is that it uses a destructive control method, the duration of which reaches 10 hours.

 Closest to the proposed technical solution is a method of dynamic calorimetry [2] consisting in measuring the heat flux (by recording the temperature difference at many points of the sample) under the assumption that the entire test sample, initially uncrystallized, took the form of a crystalline structure throughout the volume.

The disadvantage of this method is:
1) the duration of the measurement process and the process of decryption of data;
2) low accuracy of the prototype method, reaching a value of more than 10%
3) the complexity of the hardware (calorimetric in nature) design.

 The purpose of the present invention is to accelerate the process of determining the degree of crystallization and increase its accuracy.

To achieve this goal, in the proposed method for determining the degree of crystallinity of composite polymeric materials, the sample is heated until the crystalline phase is formed, and the thermal expansion rate of the sample is measured at the maximum temperature and its minimum value in the temperature range corresponding to the formation of the crystalline phase, and the degree of crystallinity determined from the ratio of the indicated linear expansion rates of the sample
h V _Tmax / V _Tmin
where V _{Tmax is} the thermal expansion rate of the sample at the maximum temperature
V _{Tmin the} rate of thermal expansion of the sample at a minimum temperature in the temperature range corresponding to the formation of the crystalline phase.

 The proposed method is illustrated by drawings.

 In FIG. 1 diagram of a device for determining small changes in the length of samples.

 In FIG. 2 is a view of a dilatogram that makes it possible to obtain the course of the change in the rate of thermal expansion at extreme temperatures and the course of the change in the temperature of the sample with constant supply of energy for its heating.

 The method is implemented using a device (dilatometer) consisting of a thermostat 1, holders 2, in which a test sample 5 is placed between two stops fixed 3 and movable 4. The movable stop 4 and sample holder 2 are equipped with lever-optical sensors of small displacements that record the change in the sample .

 The circuit is not complicated by the image of electronic communications and elements for heating the sample, measuring electrical signals, converting them into a moving light spot and other blocks that are traditional in such measurements.

 Determination of the degree of crystallinity of the polymer is as follows.

 An electric current is passed between the stops 3 and 4 through a sample of the test material placed in the thermostat 1 of the dilatometer. The sample held in the stops is heated, which, while increasing in size, moves the movable stop 4 of the dilatometer.

 At first, with increasing temperature, the elongation of the prototype is insignificant, due to the ordering of its structure, then with increasing temperature, the ductility of the structure of the composite polymer sample also increases and its expansion rate increases. After that, a sharp temporary decrease in temperature occurs when a constant current flows through the sample. The thermal expansion of the sample continues, but at a lower rate. The temperature drop in the sample is due to the formation of crystal zones of the individual components of the composite polymer, which is accompanied by the absorption of thermal energy. Then, the temperature of the sample rises again after the formation of these crystals, and the rate of linear expansion of the sample also increases.

To determine the crystallinity of composite polymeric materials, the sample is heated until the crystalline phase is formed, and the thermal expansion rates of the sample are measured at the maximum temperature and its minimum value in the temperature range corresponding to the formation of the crystalline phase, and the crystallinity is determined from the ratio of the indicated linear expansion rates sample
h V _Tmax / _Tmin
where V _{Tmax is} the thermal expansion rate of the sample at the maximum temperature,
V _{Tmin the} rate of thermal expansion of the sample at a minimum temperature in the temperature range corresponding to the formation of the crystalline phase,
The convenience of determining the degree of crystallization follows from the fact that the kinetic characteristics of the test sample are calculated directly from the crystallization curves drawn by the recorder (figure 2).

 Monochromatic light is supplied to the mirrors, then a multi-loop oscilloscope provides continuous photographic recording of several variables with time.

 The inflection zones on curves 1 and 2 are consequences of crystallization and structure ordering in the sample, since the temperature of the sample initially rises, and then (with continuous elongation) drops sharply to a certain minimum, then increases again.

The accuracy of measuring all kinetic characteristics in the dilatogram is not lower than 1% 2% and the accuracy of electrical values is not lower than 0.1%. The relative error in measuring displacements does not exceed 0.01%. Therefore, the overall accuracy of the method for determining the degree of crystallinity is 4% 5%
The measured degree of crystallinity for polymers such as polyethylene terephthalate (PET), polyhexamethylene adipamide (PHMAA), polyhexamethylene sebacianamide (PHMSCA), polyethylene sebaciamate (PESC) varied during selection for the study of various samples ranging from 0.1 to 0.9.

 Using this technical solution will improve the efficiency of the process of determining the degree of crystallinity; improve measurement accuracy, simplify hardware and reduce the decryption of the received data.

Claims (1)

 A method for determining the degree of crystallinity of materials, including heating a sample from the test material and measuring its geometric dimensions with subsequent calculation of the desired characteristic, characterized in that, in order to improve the accuracy of determining the crystallinity of composite polymer materials, the thermal expansion rate of the sample is determined at two temperatures corresponding to the initial and final stages of the formation of the crystalline phase, and the desired characteristic is determined from the ratio the indicated thermal expansion rates of the sample.

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