包装专业英语 lesson 7(2)

/dplab Plastic and polymer are often used interchangeably Smallest repetitive unit in a polymer

Smallest repetitive unit in a polymer

Monomer units are joined together to make a a larger polymer molecule But plastic tends to be used to describe finished parts polymer tends to describe raw materials Polymers can be grouped into two classes:

Thermoplastic and thermoset or commodity and engineering polymers

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2/43 Thermoplastic and thermoset or commodity and engineering polymers

日用品

Plastics: 1. plastic +s 信用卡,塑料件

2. plastics 塑料整形外科

Derived from petrochemicals

1.What elements are in the molecule? (C, H, Cl chlorine)

a water molecule has only three atoms

a typical molecule contains hundreds or thousands of atoms

2. What size (molecular weight) is the molecule?

•Today there are hundred of identified(识别，认明）species || ‘spɪːʃɪːz种类of synthetic polymer.

•Any polymer is available in a range of molecular masses, most can be modified by the addition of other monomers

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be modified by the addition of other monomers.

•In reality, the choice in plastics is almost limitless.•Properties such as melting point, stiffness will change as molecular weight changes

3. Is the molecule polar or non-polar?

It’s depending on the participating参与含有atoms [,sɔlju'biliti]

Often influence melting point , COF, solubility溶性, barrier properties

4. What shape is the molecule?

It will determine how large numbers of them will fit together

Many physical properties are affected by the molecule’s shape

5Wh t i it th l hi t?

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5. What is its thermal history?

Final property depends on it. Changing it changes the plastic’s

performance characteristics

6. What is its mechanical history?

A plastic’s final properties also depend on its mechanical history, how it flowed in the molten state and how it was stressed when

cold.

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Room temperature deformation is ‘permanent.

Plastics stretched at about T g and cooled

slowly are heat stable.

Become soft and pliable易曲折的but do not melt flow

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Plastics stretched at about T g and cooled quickly

have “memory” and will shrink if reheated.

Of its original dimensions

1.Extrusion （profile extrusion, extrusion cast

film blow film extrusion co-extrusion)

film, blow film extrusion, co-extrusion)

2.Injection molding

3.Extrusion blow molding 挤出吹塑

4.Injection blow molding (including injection

stretch blow molding)

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stretch blow molding) 注射吹塑

5.Other methods

In all thermoplastic shaping methods, the plastic must first be

heated to a point where the material has a plasticity, or fluidity.

[flu:'iditi]/dplab

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