Optical clarity crystallinity, dependence

Commercially, the film blowing process is extensively used for the production of polyolefin (LDPE, HOPE, and PP) wrapping film. Mechanical strength, optical clarity, which depends on the degree and type of crystallinity for crystalliz-able polymers, and the uniformity of thickness (variations of about 5% for films with a length scale of 10 mm to 10 m is acceptable) are the three most important and general properties of the film. 

Optical Clarity Generally increases with density. Semi-crystalline polymers usually appear opaque because of the difference in refractive index of the amorphous and crystalline domains, which leads to scat- altering. Will depend upon crystallite size. 

The eye is a complex sensory organ, which receives visual information from the environment. It encodes optical information into complex electrical signals, which are transmitted to the cortex for visual imagery through the optical nerve. The visual efficiency primarily depends on the optical clarity of the eye (e.g., cornea, crystalline lens, and intraocular media) and the neural integrity of the visual pathway (e.g., retina, optic nerve, and visual cortex). 

The occurrence of significant crystallinity in a polymer sample is of considraable consequence to a materials scientist. The properties of the sample — the density, optical clarity, modulus, and general mechanical response — all change dramatically when crystallites are present, and the polymer is no longer subject to the rules of linear viscoelasticity, which apply to amorphous polymers as outlined in Chapter 13. Howcvct, a polymer sample is rarely completely crystalline, and the properties also depend on the amonnt of crystalline order. 

The development of crystallinity may or may not be favorable depending on the end-use requirements of the PLA articles. For instance, high crystallinity will not be optimal for injection molded bottle preforms that are intended for further blow molding since rapid crystallization of the polymer would hamper the stretching of the preform and the optical clarity of the resulting bottle. In contrast, increased crystallinity will be desirable for injection molded articles for which good thermal stability is important. 

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