X‐ray diffraction orientation studies on blown polyethylene films. II. Measurements on films from a commercial blowing unit

Abstract

SynopsisX-Ray diffraction pole figure measurements have been made on a series of films, blown under various conditions from three high-density polyethylenes. The results are interpreted in terms of two distinct types of orientation. The first, and probably the more normal, is the result of the type of stress crystallization process described by Keller and Machin and has the a and c axes inclined at an angle to the plane of the film. The second type of orientation is crystallographically analogous to that found in cold drawn polyethylene in having the c-axis distribution substantially along the machine direction. This is termed high-stress orientation. The type of orientation obtained is dependent both on the blowing conditions and the particular polyethylene. With an experimental Rigidex grade and with Shell LPPE 040 there are always substantial amounts of the conventional low-stress orientation although certain combinations of machine conditions predispose towards the high-stress form. This latter type forms readily in the case of Hostalen GM 9955F over a rather wide range of machine conditions and appears to be favored by slower cooling conditions.

Correlations between processing parameters, morphology, and properties of blown films of LLDPE/LDPE blends, part 2: Crystalline and amorphous biaxial orientation by WAXD pole figures

“…This behavior suggests that the crystallographic b-and caxes were reoriented upon increasing the LDPE amount in the blends. These results are largely consistent with prior orientation studies of crystalline phase in LLDPE and LDPE blown films by WAXD and polarized IR 2,16,[17][18][19][20][21][22][23][24][25][26] and are typically interpreted in terms of the Keller-Machin I ''row nucleated'' structure. 27,28 Molecular orientation of the blends amorphous phase Many reports 8,11,12,29 have indicated that the amorphous orientation plays an important role on the final properties of the blowing films.…”

“…2,[16][17][18] Details regarding the f B calculation from the IR absorbencies were documented previously. 2,3 It must be pointed out that the crystallinity indexes used to calculate f B were the ones measured by differential scanning calorimetry (DSC).…”

Structure and Morphology Development in Films of mLLDPE/LDPE Blends During Blowing

“…This result indicates that the simultaneous presence of mLLDPE and LDPE does not cause variation in their crystal structure. There is a general agreement in literature [8,9] that the most common orientation in PE blown films is the ''a-axis'' orientation: the crystalline a-axis has a preferential orientation along the MD. The most prominent reflections are Debye-Scherer rings from the (110) and the (200) planes.…”

“…Several publications [5,[7][8][9][10][11][12][13][14] have shown that a primary cause of poor optical properties in blown polyethylene (PE) films is the surface roughness and the asperities present on the surfaces and that the orientation states of the crystalline and amorphous phases largely dictate the performance of blown films and their application.…”

X‐ray pole figures to assess orientation in PVC sheets

“…It is possible to provide a tentative explanation for this distribution by analogy with work previously reported for polyethylene. 15 Maddams and Preedy identified low and high stress crystallization orientation mechanisms. High stress crystallization produces a structure with the c-axis in the MD, and a and b axes randomly distributed as observed here.…”