Influences of melt-draw ratio and annealing on the crystalline structure and orientation of poly(4-methyl-1-pentene) casting films

Abstract

Poly(4-methyl-1-pentene) casting films with row-nucleated lamellar structure were extruded through a slit die followed by stretching using a chill roll. The influences of melt draw ratio, annealing temperature, annealing time and supplied strain level on the crystalline morphology and orientation of the poly(4-methyl-1-pentene) casting films were carefully investigated by means of scanning electron microscopy, differential scanning calorimetry, Fourier transform infrared spectrometry and X-ray diffraction. It was found that the crystalline morphology and the degree of orientation were greatly influenced by the melt draw ratio. In addition, both the changes of crystallinity and orientation degree exhibited similar tendencies (firstly increasing and then decreasing) upon increasing the free annealing temperature and time. The use of an appropriate temperature and time meant that molecular chains of the amorphous region could rearrange into a crystal lattice and defects could be removed, while an excessive annealing temperature and time could lead to partial imperfect crystals melting and recrystallizing or even disorientation phenomena. In contrast to the free annealing method, it was surprisingly discovered that annealing under supplied strain was really helpful in improving the crystalline structure and orientation of casting films.

Influence of melt-draw ratio on the crystalline behaviour of a polylactic acid cast film with a chi structure

“…This method has been widely used to fabricate polypropylene, polyethylene, polyvinylidene uoride, and poly(4-methyl-1-pentene) precursor lms with row-nucleated crystalline structures. [12][13][14][15] With the increase of melt-draw ratios, the crystallinity and orientation are enhanced.…”

The effect of melt drawing ratio on the crystal structural change and performance of polyketone extrusion cast film

“…In the process of melt stretching, the polymer usually undergoes a structural change from ellipsoid crystals to oriented lamellae and shish‐kebab crystals as the melt deformation rate increases. Our earlier works reported that HDPE, PP, PVDF, and other materials show this behavior 17,27–29 . In comparison, HDPE is easy to form a shish‐kebab structure in the melt stretching process mainly because the chain structure of polyethylene is very regular, and it can crystallize rapidly under the condition of small undercooling.…”

“…Our earlier works reported that HDPE, PP, PVDF, and other materials show this behavior. 17,[27][28][29] In comparison, HDPE is easy to form a shishkebab structure in the melt stretching process mainly because the chain structure of polyethylene is very regular, and it can crystallize rapidly under the condition of small undercooling. According to the non-isothermal crystallization experiment, we found that the crystallization speed of POK is higher than that of HDPE due to the regular chain structure and strong interaction between molecules.…”