Classification and Characteristics of Rigid Foam Plastics

Dec 21, 2020

Rigid foam refers to the foamed plastics with no flexibility, high compression hardness, high stress and a certain value, which can produce deformation and can not restore the original state after stress relief. ISO also stipulates that the foam will be compressed to 50% and the thickness of the foam will be reduced by more than 10% after the pressure is released. Its thermal insulation and mechanical properties are often used in relevant aspects. The typical products are polystyrene foam, rigid polyurethane foam, phenolic foam, amino resin, epoxy resin, thermosetting acrylic resin, and rigid polyvinyl chloride foam plastics. It can be used as thermal insulation material, sandwich material, packaging material, sound insulation and shockproof material, building material, etc.

Characteristics of foam plastics
(1) Low bulk density can reduce packing weight and transportation cost;
(2) It has excellent shock and vibration energy absorption, which can greatly reduce the damage of products when used in cushioning and shockproof packaging;
(3) It has strong adaptability to the changes of temperature and humidity, and can meet the requirements of general packaging conditions;
(4) It has the advantages of low water absorption, low hygroscopicity, good chemical stability, no corrosion to the contents, and strong resistance to acid, alkali and other chemicals;
(5) Low thermal conductivity, can be used for thermal insulation packaging, such as ice cream cup, fast food container and insulated fish box;
(6) it is easy to form and process, and can be made into various foam liners, foam blocks, sheets and so on by molding, extrusion and injection molding methods. It is easy to make two forming processes, such as foam sheet can be made into various kinds of fast food containers by thermoforming. In addition, foamed plastic blocks can also be bonded with adhesives or bonded with other materials to make various cushioning pads.

Chemical method of foaming method in this section
It can be divided into two categories: 1) chemical foaming agents, which decompose and give off gas when heated. Commonly used chemical foaming agents, such as Azodicarbonamide, azodiisobutyronitrile, dinitrosopentamethylenetetramine, sodium bicarbonate, etc. Many thermoplastic plastics can be made into foam plastics by this method. For example, PVC foam shoes, that is, resins, plasticizers, foaming agents and other additives made into the injection molding machine, the foaming agent in the cylinder decomposition, materials in the mold foaming. Foam artificial leather is mixed with PVC agent in PVC paste, coated or scraped or rolled on the fabric, through continuous tunnel heating furnace, the material is plasticized and melted, foaming agent decomposes foaming, cooling and surface finishing, then the foam artificial leather is obtained. Rigid polyvinyl chloride low foamed sheet, tube or profile is extruded to form, foaming agent is decomposed in the machine barrel. When the material is off the head, the pressure drops to atmospheric pressure. When the material is dissolved into the gas, it is expanded and foamed. If the foaming process is properly cooperated with the cooling and shaping process, the structure foam product can be obtained. (2) using the by-product gas in polymerization process, a typical example is polyurethane foam plastic. When isocyanate and polyester or polyether are polycondensation, some isocyanates will react with water, hydroxyl or carboxyl to form carbon dioxide. As long as the gas release rate and polycondensation reaction rate are properly adjusted, the high foaming products with very uniform cell can be prepared. There are two types of polyurethane foam. The soft open hole is like sponge. It is widely used in various seats, sofa cushions, sound absorbing and filtering materials, etc. the hard closed hole type is ideal insulation, insulation, shock absorption and floating materials.

classification
There are many classification methods for foam plastics, and there are three common ones.
Classification by hardness
It is divided into three categories: soft foam, rigid foam and semi rigid foam.
The elastic modulus of soft foam plastics is less than 70MPa
The modulus of elasticity of rigid foam is greater than 700MPa
Elastic modulus 70~700MPa of semi rigid foam plastics
Classification by density
It is divided into three categories: low foaming, medium foaming and high foaming plastic.
The density of low foaming foam is greater than 400kg/m3
Density of medium foamed plastics 100~400kg/m3
High foaming foam density of less than 100kg/m3

Classification by cell structure
Interconnected pores are known as open cell foams, which are called closed cell foam plastics.