Application of thermal analysis technology in traditional automotive materials

Background Introduction On January 29, 1886, Benz invented the first tricycle that did not need to be pulled by horses, and this day was also recognized as the birthday
of the car.

With the development of the times, electronic information technology is increasingly penetrating into the field of automotive electronics, and various automotive brands are striving to use richer design highlights to meet the increasingly discerning needs of
customers in order to enhance product competitiveness.

In the modern car, our life is continued on the road, and the car becomes more like a "mobile home"
.

It is estimated that the car is a complex structural vehicle composed of tens of thousands of parts, according to its power unit, conditions of use, etc.
, the specific structure of the car can be very different, but the overall structure is usually composed of four major parts of
the engine, chassis, body and electrical system.

Traditional automotive materials include thermoplastics, thermosets and rubber, which are widely used in various parts of the car, such as automotive interior parts, exterior parts, seals and tires
.

Thermal analysis techniques have a wide range of applications in these traditional automotive materials and are commonly used to test the glass transition temperature, crystallization and melting, curing, component content, creep properties, and dynamic mechanical properties
of materials.

Let's take a look at some specific test cases: Test Case 1: Identify the polymer type and estimate the component content of PC/ABS alloy is a thermoplastic made of polycarbonate (PC) and acrylonitrile-butadiene-styrene copolymer (ABS), which combines the excellent properties of the two materials, is a common automotive interior material and is also an ideal material
for the manufacture of automotive instrument panels.

PC and ABS blends form incompatible blends in which both PC and ABS are clustered in their own phases, so this blend can measure two glass transition temperatures (Tg).

Since Tg is different for different materials, we can identify the type
of polymer in the material by measuring Tg.

The content of the two components in PC/ABS has a direct impact on the performance of the material, and we can also estimate
the component content through DSC testing.

In the case of Figure 1, we tested the pure PC and the PC/ABS blend with DSC, and through the analysis of the curve, we found that the Tg of the pure PC was around
145.
7 °C.

The PC/ABS blend can measure the Tg of ABS and PC components at 110.
3 °C and 142.
9 °C
, respectively.

These two Tgs have moved toward the intermediate temperature compared to pure PCs and pure ABS
.

In addition, depending on the amount of specific heat capacity change, the content of each component in PC/ABS can also be estimated
.

The specific heat capacity change (delta Cp) of the PC in PC/ABS before and after the occurrence of Tg is 0.
182J/g· K, the delta Cp of pure PC before and after the occurrence of Tg is 0.
285J/g· K, divided by the two, the content of the PC is calculated to be about 64%.
Two.
Study of curing of thermosetting materials Epoxy resins are polycondensation products of epichlorohydrin with bisphenol A or polyols
.

Due to the chemical activity of the epoxy group, a variety of compounds containing reactive hydrogen can be used to open the ring and cure crosslinking to form a network structure
.

It is mainly used in the automotive industry as adhesives, coatings and lightweight materials
.

In the case of Figure 2, we tested the temperature rise of epoxy resin at 150 degrees at isothermal curing at different times, and according to the primary heating curve and the secondary heating curve, we can get different information
.

On the primary heating curve, we can see that as the isothermal time of epoxy resin at 150 degrees increases, Tg gradually increases, while the post-curing peak of exothermic heat gradually decreases
.

Explain that the longer the isothermal time, the higher
the curing degree of the sample.

There is also a small endothermic peak on the post-curing peak, which is produced by
the melting of the crosslinker.

Even after 140 minutes of isothermal imaging at 150 degrees, a faint peak of exothermic curing can be seen, which means that the sample is still not fully
cured at this time.

The second warming of these samples, at this time Tg is 110 degrees, and no post-curing peak is observed, which indicates that after the first warming, the sample has completely cured
.

A fully cured sample is structurally more stable and requires more energy for the glass transition to occur, so Tg is larger
than when it is not fully cured.

If we want the epoxy resin to cure as fully as possible during isothermation, we can further increase the isothermal curing temperature, or extend the isothermal curing time
of the sample.

Three.
The content of the components in the test rubber has a high elasticity
in the service temperature range compared with other materials.

In simple terms, a certain external force is applied to the rubber, the rubber can be deformed, and after the external force is removed, the rubber can return to its original state
.

This makes rubber rich in applications
.

The rubber products that are most easily seen in the car are tires, and there are many accessories
of various rubber materials on the car.

In order to make the performance of rubber meet the needs of use, oil and carbon black
are often added to the rubber.

Among them, the oil can play a role in plasticizing and reducing hardness, while carbon black plays a role
in increasing strength and improving wear resistance.

We can use TGA to test the content
of each component in rubber simply and quickly.

For acrylonitrile and halogen-containing rubber, they produce cracked carbon
when they decompose in nitrogen.

When tested with an ordinary heating program, the cracked carbon and the added carbon black will burn together under an oxidizing atmosphere, resulting in the inability to accurately obtain the content
of the added carbon black.

Since the specific surface area of carbon black is larger, the greater the activity, and the faster it burns, so we can set the back-temperature section to divide and decarbonize and add carbon when testing rubber
.

The first step that occurs at a lower temperature is the decomposition of cracked carbon, and the second step that occurs at a higher temperature is the decomposition
of added carbon black.

In the case of Figure 3, we refer to the national standard GB/T14837.
2-2014 "Rubber and rubber products Thermogravimetric analysis method to determine the composition of vulcanized rubber and unvulcanized rubber Part 2: Acrylonitrile-butadiene rubber and halogenated butyl rubber" to test
the halogen-containing rubber.

Under nitrogen, when the temperature is relatively low, volatile components and oil decomposition occur; When the temperature is slightly higher, the decomposition
of the rubber body occurs.

Then, after the temperature is switched to air, the cracked carbon produced by the decomposition of the rubber body decomposes first, and the added carbon in the rubber begins to decompose
at a higher temperature.

From this, it can be obtained that the amount of carbon black added in this type of rubber is about 10.
38%.
For customers in the automotive industry, thermal analysis techniques can be used to test
a wide range of samples.

Different thermal analysis techniques can obtain different information, including the glass transition temperature of the sample, the type of components, the component content, etc.
, which can help customers efficiently complete research and development and quality control
.