SU1295309A1 - Method of determining vitrification temperature - Google Patents

Abstract

The invention relates to a testing technique and can be used in the study of polymeric and composite materials. The purpose of the invention is to improve the accuracy of determining the glass transition temperature by ensuring that the sample loses longitudinal stability when it reaches the glass transition temperature. The sample is placed in a heating chamber and is loaded with a constant compressive force Rcr (K2El) / E2, where E is the modulus of elasticity of the material in the highly elastic state; I is the minimum axial moment of inertia of the sample cross section, f is the sample length. This formula is derived from the condition that the sample is terminated with longitudinal stability when the elastic modulus decreases to a value corresponding to the glass transition temperature (T) of the material. The sample is heated at a gradually increasing temperature, and the dependence of l f (T) of thermal elongation on temperature is measured. When the glass transition temperature is reached, the material goes into a highly elastic state and its modulus of elasticity decreases to such a value that the longitudinal stability of the sample is disturbed under the action of a compressive load. The point of buckling is clearly recorded on the Jif f (T) diagram as the point of termination or reduction of elongation with continued increase in temperature. 1 il. SL 1C with JV SO about with

Description

The invention relates to a test technique and may be used to determine the glass transition temperature of polymeric and composite materials.

The purpose of the invention is to improve the accuracy of determining the glass transition temperature by ensuring that the sample loses longitudinal stability when the glass transition temperature is reached.

The drawing shows a graph of the dependence of the heat elongation uE of the sample on the temperature T.

The method for determining the glass transition temperature is as follows.

The test core sample is placed in a heating chamber, loaded with a constant compressive force, the value of which is determined by the formula

p "p

V where E - the modulus of elasticity of the material in the highly elastic state of research institutes, MPa, I - the minimum axial moment

inertia of the sample section, M J f - sample length, m.

In this case, the magnitude of the elastic modulus of a substance in a highly elastic state, i.e. in the temperature range, their glass transition temperature, where the modulus of elasticity remains constant and does not depend on temperature, exceeds its temperature. Compression strain to which the specimen is subjected when load P is applied

KR

on

several orders of magnitude below thermal elongation, which allows us to neglect this deformation,

The value of P is chosen from the condition that the sample will lose its longitudinal stability while reducing the elastic modulus to a value corresponding to the glass transition temperature of the material.

The heating is performed and the thermal elongation of the dF f (T) of the sample is measured at a constant spherical temperature. When the glass transition temperature T is reached, the material changes to a highly elastic state; its static modulus of elasticity decreases to such a value that a violation of the longitudinal stability of the sample under the action of a compressive load occurs. The point of loss of stability is clearly recorded in the diagram.

 f (T) as a point of termination or reduction of elongation with continued increase in temperature (curve 2). This point corresponds to the temperature T j, the glass transition.

Essh1 to load the sample with the force P = P (, p, then the loss of the longitudinal stability of the sample occurs until the temperature T, glass transition (curve 1) is reached,

In the absence of load, the loss of longitudinal stability of the sample occurs at a temperature significantly higher than the temperature T ,, of the glass transition (curve 3).

An example. A sample of a binder t of a thermosetting electrolyte of the type of micasterm in the form of a rectangular rod measuring 2x20x300 mm is placed vertically in a heating chamber in which the sample is heated at a rate of 2 ° C / min. The measurement of the movement of the sample during its heating is carried out with the help of a mechanotron, on the rod of which, perceiving the elongation of the sample, is suspended a weight determined by the formula

R.P.

EG E

F

0.64 N,

35

40

where i

HER

min-Oj: 02 0jL002 T2 12 is the maximum moment of inertia of the sample section, 0.30 m is the sample length, 400 MPa is the elastic modulus of isolation of micaceous fluids at more than the approximate glass transition temperature by 30-4 ° C.

The transfer of the force developed by thermally supporting the sample is carried out by means of a quartz rigidity of the torque to the mechanotron 6M 5C. The curve 4 f (T) is recorded using a PSD-021 potentiometer. Upon reaching the temperature T, the glass transition causes the sample to lose its longitudinal stability with a sharp bend in the DE f (T) curve.

Claims (1)

Invention Formula The method of determining the glass transition temperature of a material, which continuously draws the temperature of a sample of a test material before its transition to a highly elastic state, and measures the dependence of thermal elongation of a sample on temperature, characterized in that, in order to improve the determination accuracy, the sample is loaded with a constant compressive force P, the value which is determined by the formula R where E is the modulus of elasticity of the material in a highly elastic state; I - the minimum axial moment sample inertia; f is the sample length,. and the glass transition temperature is the temperature of the sample at the moment when it loses its longitudinal stability, which corresponds to the point of termination or reduction of its thermal elongation. & t, fin