Polystyrene (PS) is generally produced in such a way that an irregular structure is formed along the main branch. In fact, the repeating units are irregular. This structure prevents crystallization. Therefore, the resulting polymer is completely amorphous (glass transition temperature = F˚210, C˚100), which makes it very transparent. This property, along with its high tensile strength and low cost, are important commercial and competitive properties of PS. However, because PS chains are so dry and brittle, they make them highly fragile. Movies made with PS are easily torn from the line when folded. Defects such as gels cause the tear to start and progress rapidly throughout the film. For these reasons, PS is usually mixed with rubber-containing modifiers such as styrene-butadiene copolymer. Although large amounts of rubber additives reduce the transparency of the film, enhance the mechanical properties of the PS film and facilitate its processability, PS films are still much harder to produce than PE films. Although PS is faster than PE cools but produces much less than PE because the film produced with PS is very sensitive and vulnerable. Great care must be taken in filtering the molten material to prevent contaminants from entering the molten material and the bubble from tearing. Also, the roll collector unit (winder) and the film cutting equipment must be designed in such a way as not to cause scratches and tears of the film.
Uses of single-layer and multi-layer PS films in the food and chocolate packaging industries, gift wrappers and special types of postal envelopes. Due to the permeability of PS films to gases such as air, especially when they use a high percentage of rubber, in the packaging industry to keep the material fresh or the fruits to arrive in stores that need to move gas ( Like air), this type of film is used.
