Multilayer structure polymer composite films are studied through thermal analysis

Introduction When we visit the supermarket in daily life, all kinds of goods will have bags, these bags are particularly light to pick up, so what is the material made of these bags? In fact, most of them are extruded by several layers of film, and then print people's favorite patterns, and eventually become the product we see, and the production process is also often used by PE film manufacturers, which is multi-layer co-extrusion technology
.

1.
Multi-layer co-delivery composite film The performance between the films can complement each other, through the complementarity between the properties of each layer of materials, high-performance composite films can be prepared, so by combining PE, PA, EVOH and other resins through multi-layer co-extrusion technology, high-quality, high-performance films
can be produced.

2.
Multilayer co-extruder production workshop and process simulation chart Experimental background This experiment is a case study of thermal property analysis of PE/PA composite multilayer film, and we use DSC, TMA and microscopy systems to carry out related explorations
.

We also need to know some basic characteristic temperature points of PE and PA before we start the study, which is a necessary step
for us to do thermal analysis of other samples.

The following figure analyzes the following figure of the multilayer film, under the heating-cooling-heating cycle of 20K/min, a temperature increase shows the melting peak (PE-LD) at about 108 °C, the shoulder peak at about 120 °C (PE-LLD), the second peak at 177 °C (PA 12) and the melting peak at the third peak 191 °C (PA 11).


The second heating run of the same sample shows four melting peaks corresponding to four different polymer compositions
.

The peak temperature through the DSC curve indicates that the multilayer film is composed
of PE-LD, PE-LLD, PA 12 and PA 11 composite materials.

The DSC test curve of multilayer film DSC 3.
The DSC test curve of multilayer film was also explored by TMA (3mm ball probe, compression mode), and the heating rate and probe pressure magnitude during TMA testing were studied to study the possible influence
of the heating rate and probe pressure size on the test results.

In Figure 4 of the METTLER TOLEDO thermomechanical analyzer, the upper figure is the test curve of TMA, and the lower figure is the first-order differential of the TMA curve, and we can read the more obvious peak temperature through the first-order differential curve, which is due to the dimensional change
caused by the melting of the components in the multilayer film during the heating process.

At the same time, we can find that when the heating rate is 20K/min, the smaller the pressure, the better the resolution for the component analysis of such multi-layer materials, and the more obvious
the shoulder peak corresponding to PA12 at 0.
1N.

4.
TMA test curve under different probe pressures Figure 5 is a multilayer film TMA test curve at different heating rates, which can be seen: when the probe pressure is consistent, the slower the heating rate, the better
the resolution.

5.
TMA test curve at different heating rates Through the above exploration, we can determine the relatively better TMA test method for such multilayer film samples, with lower heating rate and higher probe pressure resolution
.

Finally, the micromorphology of the cross-section of the film can also be analyzed by microsystems to further corroborate with the test data of DSC and TMA to clarify the material composition
of the multilayer film.

Figure 6 shows the cross-sectional micromorphology of the multilayer film, and the obvious inter-film interface can be seen, and the 7-layer co-extruded film
composed of 4 different materials (shadows) can be seen.

We can also calculate the thickness of each film through the scale of the microscope, and compare it with the dimensional change data of TMA, further clarifying that the component analysis of the film by such test methods is correct and reliable
.

6.
Cross-sectional microscopic topography of multilayer film (microscopic magnification 460 times) Summary l For the composition of such multi-layer co-extruded films, we can study and explore the test results through different thermal analysis equipment and microsystems, etc.
, to clarify the reliability
of the test results.

l In the test process, the setting of the test method also has a great impact on the accuracy of the test data, and the optimal test method
can be clarified by stepwise setting parameters and control variables.