Improvements in compressive properties of high modulus fibers by crosslinking

Sweeny, W.

doi:10.1002/pola.1992.080300618

Cited by 68 publications

(39 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The stiff polymer with its limited chain mobility prevents the radicals from recombining. A similar effect was found for other thermally crosslinked aramids [25][26][27][28] . In those cases the radicals were found to be responsible for decreasing fiber properties.…”

Section: Characterization Of Poly[1 4-phenylen-2 5-bis(prop-2-ynylosupporting

confidence: 66%

“…In the case of the latter copolymer class, both fiber spinning experiments from sulfuric acid and characterization of monofilaments before and after thermal crosslinking were described 26,27) . Other authors tried to crosslink by thermal cleavage of halogens 28) or by a c-radiation treatment [29][30][31] . Furthermore, several aramids containing unsaturated groups were synthesized, e. g. N-allyl- 32) , alkinyl- 33,34) and maleimidyl- 35,36) substitution of the aromatic backbone.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

An investigation of novel approaches in order to provide crosslinked fully aromatic polyamide chains

Glomm¹,

Oertli²,

Rickert³

et al. 2000

Macromol. Chem. Phys.

View full text Add to dashboard Cite

Two different, novel approaches to crosslink fully aromatic, rigid‐rod aramid chains were studied. First, the new rigid‐rod aramid poly[1,4‐phenylen‐2,5‐bis(prop‐2‐ynyloxy)‐terephthalamide] with an inherent viscosity of ηinh = 2.74 dL/g was synthesized by low temperature polycondensation of p‐phenylendiamine and 2,5‐bis(prop‐2‐ynyloxy)‐terephthaloylchloride. The pendant alkinyl moieties allowed thermally induced crosslinking at temperatures higher than 200°C. No weight loss was found due to this treatment, but curing gave rise to the formation of stable radicals. However, no fiber spinning experiments were carried out using this material due to the insufficient stability of the polymer chains against degradation when being dissolved in sulfuric acid. Furthermore, fibers of a rigid rod polyamide containing pyrimidine moieties, produced by polycondensation of bis‐silylated 2,5‐diaminoprimidine and terephthaloyl dichloride, were spun from nematic solutions. Fibers were crosslinked by complexation with nickel(II)‐ions in the swollen state. Both crosslinked and non‐crosslinked, otherwise identically processed samples, were characterized by wide‐angle X‐ray‐diffraction (WAXD) measurements and mechanical tests. A post‐spin heat treatment was employed to improve the low degrees of orientation and crystallinity that the untreated fibers in general showed. The dominating crystal structures of both fiber samples are similar to “Modification II” of the well characterized fibers from poly(p‐phenylene‐terephthalamide) (PPTA). The number and size of the morphological defects in the crosslinked fibers was significantly higher than in the non‐crosslinked samples. The influence of the annealing on the mechanical fiber properties and the molecular order in the fibers was investigated. The values of all mechanical parameters were considerably lower in the case of the crosslinked fibers, probably due to the collapse of the entire supramolecular order and fiber morphology.

show abstract

Section: Characterization Of Poly[1 4-phenylen-2 5-bis(prop-2-ynylosupporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

An investigation of novel approaches in order to provide crosslinked fully aromatic polyamide chains

Glomm¹,

Oertli²,

Rickert³

et al. 2000

Macromol. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…This system showed a marginal improvement in compressive strength upon heat treatment. 8 Sweeny 9 reported a halogenated PBZT system that, when heat treated, resulted in a slight increase in compressive strength. Dotrong et al 10,11 has investigated a dimethyl-phenoxy PBZT system that was expected to crosslink upon heat treatment.…”

Section: Introductionmentioning

confidence: 99%

Modeling the effect of crosslinking in methyl-pendant poly(p-phenylene benzobisthiazole)

Jenkins

Jacob

Kumar

1998

J. Polym. Sci. B Polym. Phys.

View full text Add to dashboard Cite

Molecular mechanics and dynamics simulations have been performed on methyl‐pendant PBZT to study the effects of intermolecular crosslinking. Several possible crosslinked structures were investigated. The effect of crosslinking was found to be strongly dependent upon crosslink type and, in some instances, crosslink density. A significant axial stress is predicted to occur upon the formation of phenyl‐to‐phenyl type crosslinks. This provides a reasonable explanation for the experimental observation of transverse cracks in the skin of crosslinked, MePBZT fiber. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3057–3064, 1998

show abstract

“…There have been many efforts to improve the compressive strength of fibers made from the rigid-rod polymers by increasing the transverse interactions at the polymer chain level. These include crosslinking at the molecular level [2,3,7,8,22] and incorporation of bulky groups in the backbone of the polymer to disrupt their nematic packing order [23]. However, only a limited degree of success has been achieved with these molecular modifications, suggesting that the compressive strength of these fibers depends more on interactions at the fibril level rather than at the moleoular level.…”

mentioning

confidence: 99%

Mechanical Property Modification of Aramid Fibers by Polymer Infiltration

Mathur

Netravali

1996

Textile Research Journal

View full text Add to dashboard Cite

High performance organic fibers such as Kevlar, which are highly fibrillar in nature, possess excellent mechanical properties under tension but exhibit very poor strength in compression due to poor interfibrillar attraction. This study involves infiltrating polymeric materials into single aramid filament networks to improve interfibrillar adhesion and thus modify their mechanical properties. Wet-never-dried aramid fibers are used in this study, but it is still necessary to further open the fibrillar network with concentrated sulfuric acid to effectively infiltrate the polymer. While there is significant improvement in tensile strength after polymer infiltration, this is offset by a loss in strength due to the acid treatment. However, there is a significant increase of over 33% in compressive strength as a result of infiltration. The infiltration technique shows excellent promise and could be used for tailoring the properties of fibers with fibrillar morphology for selective end-use applications.Over the past twenty years, polymer and fiber technologists have focused their attention on the development of fiber formation processes to obtain high crystallinity and almost perfect orientation of extended molecular chains in the solid state. These efforts, as well as the development of novel liquid crystalline polymers (LCP), have resulted in several high. performance organic fibers whose strength and moduli values have come closer to the theoretical values. Fibers belonging to this category include aramids such as Kevlar, Technora, TwaronT~'', and other organic fibers such as PBI (poly-benzimidazole), Spectra&dquo; (ultra high molecular weight polyethylene), and PBZT (poly-paraphenylene benzobisthiazole).In LCP fibers such as Kevlar 49, developed by Dupont, the extended chain morphology of poly-paraphenylene terephthalamide (PPTA) molecules, the high crystallinity, and the presence of aromatic rings in the polymer chain are responsible for the high modulus, strength, and chemical and thermal stability [24, 5].The near perfect axial orientation of the extended molecular chains in these fibers results, however, in their highly anisotropic mechanical properties [9,12]. Another reason for the high anisotropy is the strong covalent bonds along the fiber axis as compared to the weak hydrogen bonding and Van der Waals attraction in the transverse direction.The compressive strength of Kevlar fibers is less than 20% of the tensile strength, while the axial shear modulus is less than 2% of the axial tensile modulus of the fibers [24]. This is a significant drawback when using these fibers in composite materials for some sppiications. There have been many efforts to improve the compressive strength of fibers made from the rigid-rod polymers by increasing the transverse interactions at the polymer chain level. These include crosslinking at the molecular level [2,3,7,8,22] and incorporation of bulky groups in the backbone of the polymer to disrupt their nematic packing order [23]. However, only a limited degree of success has been...

show abstract

Improvements in compressive properties of high modulus fibers by crosslinking

Cited by 68 publications

References 5 publications

An investigation of novel approaches in order to provide crosslinked fully aromatic polyamide chains

An investigation of novel approaches in order to provide crosslinked fully aromatic polyamide chains

Modeling the effect of crosslinking in methyl-pendant poly(p-phenylene benzobisthiazole)

Mechanical Property Modification of Aramid Fibers by Polymer Infiltration

Contact Info

Product

Resources

About