High-density polyethylene (HDPE) is widely used in pharmaceutical packaging, such as high-density polyethylene medicinal ointment boxes, due to its excellent mechanical properties, chemical stability, and processing performance. However, HDPE has limited chemical barrier properties for oily ointments; small molecules in oils can permeate through the intermolecular gaps in HDPE, affecting the quality and stability of the ointment. Blending modification, by combining HDPE with other materials possessing excellent barrier properties, can effectively improve its chemical barrier performance against oily ointments.
The core of blending modification lies in selecting suitable blending materials. Commonly used high-barrier materials include polyamide (PA), ethylene-vinyl alcohol copolymer (EVOH), and acrylonitrile-styrene copolymer (AS). These materials possess polar groups or highly crystalline structures, effectively preventing the permeation of small molecules. For example, PA, due to its excellent oil resistance and gas barrier properties, is an ideal choice for blending with HDPE. By blending PA with HDPE, PA forms a layered or lamellar structure within the HDPE matrix, extending the diffusion path of oil molecules and thus significantly improving barrier performance.
To achieve good blending of HDPE and PA, the poor compatibility between the two must be addressed. Since HDPE is a non-polar polymer and PA is a polar polymer, direct blending leads to weak interfacial bonding, affecting barrier performance. Therefore, compatibilizers are needed to improve compatibility. Commonly used compatibilizers include polyethylene containing carboxylic acid or anhydride groups, such as maleic anhydride-grafted polyethylene (PE-g-MAH). Compatibilizers form chemical bonds at the HDPE-PA interface through chemical reactions, enhancing interfacial bonding and allowing PA to be uniformly dispersed in HDPE, forming a continuous barrier layer.
The blending process is crucial for improving barrier performance. During blending, parameters such as processing temperature, shear rate, and screw speed must be controlled. High temperature and appropriate shear force help PA form a layered structure in HDPE, but excessive shear force may cause the PA layered structure to break, reducing barrier performance. Therefore, the blending process needs to be optimized to ensure that PA is uniformly dispersed in HDPE in a layered or sheet-like form. Furthermore, screw speed and residence time also affect the morphology of the blend, requiring experimental determination of optimal process conditions.
Multilayer co-extrusion technology is an effective means to further improve barrier properties. By co-extruding HDPE and PA into a multilayer structure, such as an HDPE/PA/HDPE three-layer composite, each layer performs a different function: the outer HDPE layer provides mechanical strength and processing performance, while the middle PA layer provides barrier properties. This structure not only improves the overall barrier effect but also retains the processing advantages of HDPE. Multilayer co-extrusion technology requires precise control of the thickness of each layer and the interfacial bonding to ensure no defects between layers, thereby achieving optimal barrier performance.
The introduction of nanofillers provides a new approach to blend modification. Nanofillers such as montmorillonite (MMT) have a layered structure and high specific surface area, which can significantly improve the barrier properties of polymers. Combining nanofillers with HDPE/PA blends, the nanofillers form a "maze" effect in the matrix, further extending the diffusion path of oil molecules. Furthermore, nanofillers can enhance the mechanical properties and thermal stability of materials, improving the overall performance of high-density polyethylene medicinal ointment boxes.
Through blending modification, the chemical barrier properties of HDPE high-density polyethylene medicinal ointment boxes for oil-based ointments are significantly improved. The selection of blending materials, the addition of compatibilizers, the optimization of the blending process, the application of multilayer co-extrusion technology, and the introduction of nanofillers collectively constitute the key factors in improving barrier performance. In the future, with the continuous advancement of materials science and processing technology, blending modification will play an even greater role in the pharmaceutical packaging field, providing more reliable guarantees for the quality and stability of pharmaceuticals.
