**Part 1**

**Basics for Injection Molding** 

**1** 

Jian Wang

*China* 

**PVT Properties of Polymers** 

*School of Chemical Engineering and Environment, Beijing Institute of Technology,* 

PVT (Pressure-Volume-Temperature) properties of polymers are important for both engineering and polymer physics. Fig.1 shows the typical PVT diagrams of an amorphous (a) and semi-crystalline polymer (b). PVT diagram describes the specific volume as a function of pressure and temperature. Specific volume increases with the temperature increasing. There is a thermal transition in the polymer. The primary amorphous transition of any polymer is known as its glass transition temperature, Tg. While Tg is not a sharp transition, the data from below and above Tg will show an intersection that is generally accepted as being Tg. As shown in Fig. 1, semi-crystalline polymer exhibits a different thermal response than amorphous polymer. For the amorphous polymer, Tg is clearly seen as the temperature where the polymer goes from a solid to a melt. The rate of expansion per temperature increment is much smaller in the solid state than in the melt state. By contrast, the semi-crystalline polymer contains sufficient crystallinity to maintain structural continuity above Tg. While the amorphous content in this polymer exhibits a Tg, the crystal structure allows characterization up to nearly the temperature where the crystals melt.

Polymer PVT data become increasingly important in their value in material science. The excess usage of PVT data can be summarized in at least eight major areas (Berry et al., 1998;

Prediction of service performance and service life of polymeric materials and

Correlation of the reducing parameters of equations of state (EOS) with molecular

Evaluation of start and progress of chemical reactions in polymer melts in the cases

Optimizing of processing parameters instead of establishing such parameters by trial

Injection molding is the most common technique for the mass production of complex shaped products that require accurate dimensions. In injection molding process, some

**1. Introduction** 

Hess, 2004):

structures;

and error;

Prediction of polymer-polymer miscibility;

components on the basis of free volume concepts;

when volume effects accompany the reaction;

Calculation of the surface tension of polymer melts.

Investigation of the nature of phase transitions;

Materials properties of systems in contact with solvents or gases;

 **for Injection Molding** 
