Surface morphology in semicrystalline polymers

Fitchmun, D. R.; Newman, Seymour

doi:10.1002/pol.1969.110070410

Cited by 44 publications

(10 citation statements)

References 8 publications

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“…It was found that the SMPU prepared in the chaotic mixer contained higher soft segment crystallinity than the materials prepared in Brabender internal mixer (figure 2a). The polar-polar interactions between ox-CNF and SMPU may have promoted adsorption of polymer chains on the fiber surface, which in turn induced favorable chain conformations and hence higher rates of nucleation and crystallization [18] [19,20]. Of the filler particles studied, CB was observed to exert weak influence on the soft segment crystallinity, while the presence of CNF and ox-CNF greatly reduced the soft segment crystallinity irrespective of the mixer used.…”

Section: Resultsmentioning

confidence: 99%

Shape Memory Actuation by Resistive Heating in Polyurethane Composites of Carbonaceous Conductive Fillers

2008

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The dependence of electrical resistivity on specimen temperature and imposed tensile strains was determined for shape memory polyurethane (SMPU) composites of carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), and carbon black (CB). The SMPU composites with crystalline soft segments were synthesized from diphenylmethane diisocyanate, 1,4butanediol, and poly(caprolactone)diol in a low-shear chaotic mixer and in an internal mixer. The materials synthesized in the chaotic mixer showed higher soft segment crystallinity and lower electrical percolation thresholds. The soft segment crystallinity reduced in the presence of CNF and ox-CNF; although the reduction was lower in the case of ox-CNF. The composites of CB showed pronounced positive temperature coefficient (PTC) effects which in turn showed a close relationship with non-linear thermal expansion behavior. The composites of CNF and ox-CNF did not exhibit PTC effects due to low levels of soft segment crystallinity. The resistivity of composites of CNF and ox-CNF showed weak dependence on strain, while that of composites of CB increased by several orders of magnitude with imposed tensile strain. A corollary of this study was that a high level of crystallinity may cause a PTC effect and prevent any actuation through resistive heating. However, a carefully tailored compound which has reduced crystallinity and which requires minimum amount of filler may prevent PTC phenomenon and could supply necessary electrical conductivity over the operating temperature range, while offering enough soft segment crystallinity and rubberlike properties for excellent shape memory function.

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Section: Resultsmentioning

confidence: 99%

Shape Memory Actuation by Resistive Heating in Polyurethane Composites of Carbonaceous Conductive Fillers

2008

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“…There are usually one or more Iayers between the skin and core that are transitional shear zones with intermediate structure. In polyacetals this has been termed 'transcrystallinity' [194,179]. Transcrystalline growth is controlled by the heat flow to the mold wall and is initiated by the cold mold wall.…”

Section: Multilayered Structuresmentioning

confidence: 99%

Polymer applications

Sawyer¹,

Grubb²

1996

Polymer Microscopy

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“…The skin surface in the microtomed section (top in Fig. In polyacetals this has been termed 'transcrystallinity' [159,146]. The molecular chains are oriented parallel to the injection direction.…”

Section: Multilayered Structuresmentioning

confidence: 99%