Supercritical fluid CO₂ technology is a new and clean isolation technology, which exploits the special dissolving capacity of CO₂ and target substance under supercritical condition by controlling CO₂ pressure, temperature, etc.,to dissolve and isolate target substance.
Compared with other traditional processes, it shows incomparable advantages, such as, using inert gas assolvent, cheap and easily accessible; pollution-free and environment-friendly; simple process; no residue of chemical solvent in target substance which guarantees the quality of target product.
Microcellular foamed polymer
The microcellular foamed polymer refers to a porous polymer material having a cell size of from 1 μm to 100 μm.Compared with unfoamed polymer, it has light weight, excellent sound insulation and thermal insulation properties, and overcomes the shortcomings of poor mechanical properties of traditional foam plastics.
Microporous polymer materials can be used infood packaging, insulation materials, and controlled release systems.Polylactic acid (PLA) is an important biodegradable polymer material which canbe fermented by fermentation of corn and plant straw and then polymerized. Itcan replace existing petroleum-based polymer materials and effectively alleviate the pressure caused by the declining oil resources.
Because of its good biocompatibility and processability, it has been widely used in fracture fixation, tissue engineering scaffold materials, drug controlled release systems and packaging materials.
Traditional foam materials have poor toughness, large waste volume, are difficult to handle, and produce toxic gases that can pollute the environment when burned.
Methods for preparing the foamed material of polylactic acid mainly
At present, the methods for preparing the foamed material of polylactic acid mainly include a heat-guided phase separation method, a monomer polymerization method, and a supersaturated gas method.
However, due to the long production cycle, continuous production, and low efficiency, the demand for foamed materials of polylactic acid is large.
Polylactic Acid Foaming Material By Supercritical CO2 Equipment
Supercritical gas fluid refers to a fluid that exceeds the street temperature and critical pressure of a substance. Under supercritical conditions, CO2 has a density similar to that of a liquid, has the strength of a conventional liquid solvent, and it has a viscosity of a gas, and has a high Mass transfer rate.
Supercritical CO2 has a good plasticizing effect on the polymer melt, can reduce the viscosity of the polymer melt, improve the fluidity of the melt, lower the extrusion temperature, and has non-toxic, non-flammable, ODP as a foaming agent. Zero, safety, high foaming efficiency and so on.
We used supercritical CO2 as a foaming agent to study the foaming process of polylactic acid. The effects of foaming temperature, saturation pressure, depressurization rate and crystallinity on the morphology of PLA micropores were investigated, and the micropore formation process was carried out.
Analysis improves the performance of polylactic acid foamed materials and provides a new way to reduce material costs.
Supercritical fluid foam molding
Supercritical foam molding is a physical foam molding technology, and it is also a microcellular foam molding technology. It is used in the injection, extrusion and blow molding processes to first remove supercritical carbon dioxide or nitrogen and other The gas is injected into a special plasticizing device to make the gas and the molten raw material fully mix/diffuse to form a single-phase mixed sol, and then guide the sol into the mold cavity or extrusion die to cause the sol to produce a large pressure drop. As a result, the gas precipitates to form a large number of bubble nuclei; in the subsequent cooling and molding process, the bubble nucleus inside the sol continuously grows and forms, and finally a microcellular foamed plastic product is obtained.
Characteristics of supercritical fluid foaming
- Compared with ordinary AC foaming agent, the foamed foam is cleaner and the coloring performance is better. AC foaming agent is yellow crystals, and the decomposition is easy to produce more by-products, resulting in product taste and color deviation.
- The foam cells foamed by supercritical fluid are more delicate and have better dispersibility compared with AC foaming agent.
- Supercritical foamed foam can be lighter and its density can reach 15Kg/m3.
- The supercritical foamed foam has greater impact strength, better thermal stability, toughness, good sound insulation performance, lower thermal conductivity and thermal conductivity.
Performance analysis of supercritical foam material:
① Supercritical foamed products have a finer and more uniform cell structure, which can improve the mechanical properties of the material.
② The cell size of the microporous structure is smaller than the defects inside the material. The existence of cells will not reduce the strength of the material. Due to the existence of micropores, the original crack tips in the material will be passivated, which helps prevent cracks from under stress. Expansion, thereby improving the mechanical properties of plastics.
Microporous plastic products have high specific strength and high cost performance, which can greatly improve the dimensional accuracy of products and shorten the product development cycle; greatly reduce product residual stress and reduce product warpage deformation; eliminate surface sink marks; shorten the molding cycle of thin-walled products; Effectively save raw materials and reduce product quality; low cost of foaming agent and environmental protection; mixed sol fluidity increased by 20% to 40%, low viscosity, easy to fill molds; supercritical gas equipment has simple process, low cost, and environmental protection.