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Crystallinity Issues in Biaxially Stretch Films
2024-09-13
1. Introduction
Crystallinity, as an important parameter to characterize material properties, directly affects the physical, chemical and mechanical properties of the film, especially in the biaxially oriented film production line. High crystallinity often means that the material has better dimensional stability, strength, hardness, stiffness and heat and chemical resistance, but it may also lead to a decrease in properties related to chain movement such as elasticity, elongation at break, and impact strength. Therefore, accurate measurement and control of film crystallinity is of great significance for scientific research and industrial production of biaxially oriented films.
2. Definition of crystallinity
Crystallinity usually refers to the proportion of the crystalline region in a polymer, which can be expressed as the mass fraction or volume fraction of the crystalline region. Since the boundary between the crystalline region and the non-crystalline region of a polymer is not clear, the measurement and calculation of crystallinity may sometimes be inconsistent.
3. Crystallinity detection method
- X-ray diffraction (XRD)
X-ray diffraction is a commonly used method for measuring crystallinity. It uses the characteristics that the wavelength of X-rays is close to the lattice constant of the crystal to determine the crystallinity of the crystal by measuring the diffraction pattern of X-rays. When the crystallinity of the crystal is higher, its diffraction pattern is clearer and the diffraction peak is sharper. The basic structure of the X-ray diffractometer is an X-ray source, an adjustment mechanism system, a radiation detector, and a diffraction pattern processing and analysis system, which can provide a highly stable X-ray source and obtain accurate measurement results through automated and intelligent dedicated diffraction pattern processing and analysis software.
- Thermal difference method
The thermal difference method is a method for determining the crystallinity by measuring the length change of the crystal during heating or cooling. When the crystallinity of the crystal is higher, its thermal expansion coefficient is smaller and the thermal difference is smaller. This method is simple and direct and is suitable for quickly determining the crystallinity of the material.
- Optical microscopy method
Optical microscopy is a method for determining the crystallinity by observing the microscopic structure of the crystal. When the crystallinity of the crystal is higher, its microscopic structure is clearer and the crystal surface is smoother. This method is suitable for observing the microstructure of materials, but may be limited by sample preparation and observation conditions.
- Thermal analysis
Thermal analysis is a method for determining crystallinity by measuring the heat change of a crystal during heating or cooling. The higher the crystallinity of a crystal, the smaller its heat capacity and the steeper the thermal analysis curve. This method is suitable for analyzing the thermal stability and thermal decomposition characteristics of a material.
- Differential scanning calorimetry (DSC)
Differential scanning calorimetry is a method for determining crystallinity by measuring the heat flow difference between a sample and a reference under programmed temperature control. This method can accurately measure parameters such as the melting temperature and melting enthalpy of a material, thereby calculating the crystallinity of the material.
4.Application of crystallinity detection
Crystallinity detection is widely used in the performance analysis and quality control of a variety of materials such as polymers, alloys, fibers, nylon, textile materials, polypropylene, polyethylene, polyester, injection molded parts, powders, plastics, polymers, composite materials, films, carbon materials, inorganic materials, polylactic acid, etc. By accurately measuring the crystallinity of a material, the production process of the material can be optimized and the quality and performance of the product can be improved.
5. Conclusion
Crystallinity detection is an indispensable part of film biaxial stretching scientific research and industrial production. By selecting appropriate detection methods and technical means, the crystallinity of the material can be accurately measured, providing strong support for film performance analysis and quality control. With the continuous development of science and technology, crystallinity detection technology will also be continuously updated and improved, bringing more convenience and benefits to film scientific research and industrial production.
