Morphological considerations on the mechanical properties of blown high-density polyethylene films

Kim, Yong‐Man; Kim, Chul‐Hwan; Park, Jung-Ki; Lee, Cheol-Woo; Min, Tae-Ik

doi:10.1002/(sici)1097-4628(19970118)63:3<289::aid-app3>3.0.co;2-j

Cited by 25 publications

(14 citation statements)

References 1 publication

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“…4(a)] is orthogonal to the SALS orientation shown in Figure 10. SAXS, SALS, and optical microscopy indicate that lamellae stacked within the rodlike structures of Figure 9 are normal to the fiber axis, which is consistent with stacked lamellar morphologies 21–23…”

Section: Methodssupporting

confidence: 62%

“…The second question might be answered by the consideration of the possibility of stacked lamellar structures within the linear domains seen in light scattering and optical microscopy. These stacked lamellar structures have been observed in blown and oriented HDPE films and are composed of around 3–10 lamella stacked together in blocks 21–24. The lamellae in these stacked lamellar structures are typically oriented with the basal planes almost perpendicular to the MD–TD plane and their surface normals parallel to the MD.…”

Section: Discussionmentioning

confidence: 87%

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Optical properties and orientation in polyethylene blown films

Bafna

Beaucage

Mirabella³

et al. 2001

J Polym Sci B Polym Phys

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ABSTRACT:We report structural factors affecting the optical properties of blown polyethylene films. Two types of blown polyethylene films of similar degrees of crystallinity were made from (1) single-site-catalyst high-density polyethylene (HDPE; STAR ␣) and (2) Ziegler-Natta-catalyst HDPE (ZN) resins. The STAR ␣ film exhibited high clarity and gloss, whereas the ZN film was turbid. Small-angle X-ray scattering (SAXS), small-angle light scattering (SALS), and optical microscopy gave quantitative and qualitative information regarding structure and orientation in the films. A new approach is described for determining the three-dimensional lamellar normal orientation from SAXS. Both the clear STAR ␣ and turbid ZN films had similar lamellar crystalline structures and long periods but displayed different degrees of orientation. It is demonstrated that optical haze is related to surface features that seem to be linked to the bulk morphology. The relationship between haze and structural orientation is described. The lamellar orientation is linked to rodlike structures seen in optical microscopy and SALS through a stacked lamellar or cylindrite morphology on a nanometer scale and through a fiberlike morphology on a micrometer scale. The micrometer-scale, rodlike structures seem directly related to surface roughness in a comparison of index-matched immersion and surface micrographs. The higher haze and lower gloss of the ZN film was caused by extensive surface roughness not observed in the STAR ␣ film.

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Section: Methodssupporting

confidence: 62%

Section: Discussionmentioning

confidence: 87%

Optical properties and orientation in polyethylene blown films

Bafna

Beaucage

Mirabella³

et al. 2001

J Polym Sci B Polym Phys

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“…The twist of lamellae about the b axis in the LS structure does not fundamentally alter this argument; such twisting rotates the long dimension of the amorphous interlayers through the TD/film‐normal plane, but never along the MD direction, which thus remains the direction with the highest tear strength. The opposite behavior would then be expected for linear polyethylenes, such as LLDPE and HDPE, for which propagating a tear along MD, either between coherent lamellar stacks5 or through the crystals themselves (breaking only van der Waals bonds), is easier than tearing along TD, for which covalent bonds in the tie molecules would need to be broken. These contrasting behaviors are shown schematically in Figure 5.…”

Section: Resultsmentioning

confidence: 93%

“…However, not all polyethylenes behave as LDPE does;2 for example, blown films of high‐density polyethylene (HDPE) generally tear along MD,3–7 rather than TD. This comparison is clouded by the fact that polyethylenes can form different structures in blown films; for example, LDPE typically shows3, 10 the Keller–Machin low‐stress (LS) structure,11 whereas HDPE can show either the LS3, 8, 12, 13 or high‐stress (HS)13, 14 structure.…”

Section: Introductionmentioning

confidence: 99%

Tear anisotropy in films blown from polyethylenes of different macromolecular architectures

Lee

Dean

2005

J Polym Sci B Polym Phys

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Blown films of different types of polyethylenes, such as branched low‐density polyethylene (LDPE) and linear high‐density polyethylene (HDPE), are well known to tear easily along particular directions: along the film bubble's transverse direction for LDPE and along the machine direction (MD) for HDPE. Depending on the resin characteristics and processing conditions, different structures can form within the film; it is therefore difficult to separate the effects of the crystal structure and orientation on the film tear behavior from the effects of the macromolecular architecture, such as the molecular weight distribution and long‐chain branching. Here we examine LDPE, HDPE, and linear low‐density polyethylene (LLDPE) blown films with similar crystal orientations, as verified by through‐film X‐ray scattering measurements. With these common orientations, LDPE and HDPE films still follow the usual preferred tear directions, whereas LLDPE tears isotropically despite an oriented crystal structure. These differences are attributed to the number densities of the tie molecules, especially along MD, which are considerably greater for linear‐architecture polymers with a substantial fraction of long chains, capable of significant extension in flow. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 413–420, 2005

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“…The tear properties of Biomax have also been investigated in order to establish the tear mechanism for this polymer. As molecular orientation within a sample is known to produce regions with different tensile and tear characteristics, samples from both machine and transverse directions were examined [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

The Tensile and Tear Properties of a Biodegradable Polyester Film

Nissen

Stuart

Stevens

et al. 2008

International Journal of Polymer Analysis and Characterization

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The tensile and tear properties of a biodegradable polymer, Biomax, have been studied in order to assess this material in film applications. While the tensile strength of Biomax was comparable to low density polyethylene, the tear strength was found to be six times lower. A study of the load-displacement curves revealed a regular variation in the load throughout the test, which was attributed to the presence of lower and higher strength regions in the polymer.The higher strength regions were characterised by the presence of polymer chains oriented parallel to the tear surface, while the lower strength regions were defined by an absence of molecular orientation and the presence of voids.

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Morphological considerations on the mechanical properties of blown high-density polyethylene films

Cited by 25 publications

References 1 publication

Optical properties and orientation in polyethylene blown films

Optical properties and orientation in polyethylene blown films

Tear anisotropy in films blown from polyethylenes of different macromolecular architectures

The Tensile and Tear Properties of a Biodegradable Polyester Film

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