Chapter One Basic Knowledge of Plastic Packaging (I)

1. What are monomers, polymers, homopolymers, copolymers?
A: Polymers are a type of compound with a large relative molecular mass and are all formed by the polymerization of one or more simple compounds (usually called monomers). They are the main components in plastics. They play a dominant role in the bonding of all components and determine whether the plastic is thermoset or thermoplastic. It is an important factor affecting the physical, chemical, and mechanical properties of plastics. Their content in plastics is generally 30% to 90%. Not strictly speaking, a polymer obtained by a polymer or a polymer compound is called a homopolymer, and a polymer obtained by polymerizing two or more monomers is called a copolymer.

2. What is a linear polymer compound? How is it characteristic?
Answer: The polymer compound of a chain structure in which many monomer units are linked to each other is called a linear polymer compound or a chain polymer compound. This kind of polymer compound can swell in a solvent and dissolve. Softened by heat and able to flow. The vast majority can be melted without decomposition and can be melted repeatedly several times. Has good elasticity and plasticity. Most can be cold-rolled or rolled to increase their degree of molecular orientation. Most thermoplastic plastics are linear polymer compounds.

3. What is a body-shaped polymer compound? How is it characteristic?
A: It is a macromolecular compound with a three-dimensional structure in which a functional group capable of reacting on a linear polymer chain forms a direct link or a monomer is directly polymerized under certain conditions. The body-shaped polymer compound is a "giant molecule". There is no limit to the volume and relative molecular mass of the molecule, and often one product is a huge volume molecule. Therefore, the relative molecular mass has lost its meaning to it. It cannot be dispersed by solvent molecules (but it can be swollen by solvents), it cannot be heated and it is an insoluble compound. The shape polymers are amorphous, always in the glassy state, very hard, brittle, usually not elastic, heating does not soften, plasticizers do not work on it, and cold stretching or roll pressing cannot make the molecules oriented. However, the formation of body-shaped polymers is often performed in stages, that is, the shape of the line-shaped meridian finally becomes a body shape. If the body-shaped structure is not formed before the compression molding is performed, heating is performed so that the reaction is completed during the blooming process. Get a hard product. Generally referred to as thermosetting plastics, most are body-shaped polymer compounds.

4. Is resin and plastic the same concept?
A: Resin is a synthetic polymer compound. The plastics are based on polymer materials, with or without addition of other additives, capable of molding materials under certain temperature and pressure conditions. Therefore, if it is popular to say that the resin belongs to the category of plastic, the plastic contains the resin. But resins and plastics are two concepts that are related to each other.

5. What are the main characteristics of plastics?
A: All kinds of plastics have various characteristics. Here we can only discuss the versatility of plastics or the characteristics of common plastics. (See Table 1-1).
(1) Excellent properties of plastics 1 Most plastics are light, chemically stable, and will not rust;
2 The impact resistance must be better, and it is not easy to break when falling;
3 generally have transparency, wear resistance;
4 moldability, good coloring, low processing costs;
5 good insulation, poor thermal conductivity.
(2) Defects in plastics 1 Most plastics have poor heat resistance, and their physical properties at high temperatures are significantly reduced, and they have large thermal expansion rates and are easily combustible.
2 It is easy to deform when a large load is applied, and some kinds of strains also deform when used at room temperature, and the dimensional stability is poor;
3 Most plastics are brittle at low temperatures;
4 easy to react with organic solvents;
5 easy to aging;
6 Less strength and toughness than metal materials.

Table 1-1 Performance of Common Plastics