Ultimate Tensile Properties Research Articles

Melt miscibility and mechanical properties of metallocene linear low‐density polyethylene blends with high‐density polyethylene: influence of comonomer type

AbstractIn this paper, the implications of melt miscibility on the thermal and mechanical properties of linear low‐density polyethylene (LLDPE)/high‐density polyethylene (HDPE) blends were assessed with respect to the influence of the comonomer type. The influence of the latter was examined by selecting one butene LLDPE and one octene LLDPE of very similar weight‐average molecular weight (Mw), molecular‐weight distribution (MWD) and branch content, keeping the comonomer type as the only primary molecular variable. Each of the two metallocene LLDPEs was melt‐blended with the same HDPE at 190 °C in a Haake melt‐blender. The rheological, thermal and mechanical properties were measured by the use of an ARES rheometer, differential scanning calorimeter and Instron machine, respectively. The rheological measurements, made over the linear viscoelastic range, suggested no significant influence of the branch type on the melt miscibility. The rheology results are in agreement with those obtained from previous transmission electron microscopy (TEM) and small‐angle neutron scattering (SANS) studies. The dynamic shear viscosity and total crystallinity of the metallocene (m)‐LLDPE blends with HDPE followed linear additivity. At small strains, the branch type has little or no influence on the melt miscibility and solid‐state properties of the blends. Even the large‐strain mechanical properties, such as tensile strength and elongation at break, were not influenced by the comonomer type. However, the ultimate tensile properties of the HDPE‐rich blends were poor. Incompatibility of the HDPE‐rich blends, as a result of the weak interfaces between the blend components, is suggested to develop at large strains. Copyright © 2005 Society of Chemical Industry

Stress–strain behavior of low‐density polyethylene/poly(methyl methacrylate) blends with modulated interfaces with a hydrogenated polybutadiene‐block‐poly(methyl methacrylate) diblock copolymer

AbstractThe stress–strain diagrams and ultimate tensile properties of uncompatibilized and compatibilized hydrogenated polybutadiene‐block‐poly(methyl methacrylate) (HPB‐b‐PMMA) blends with 20 wt % poly(methyl methacrylate) (PMMA) droplets dispersed in a low‐density polyethylene (LDPE) matrix were studied. The HPB‐b‐PMMA pure diblock copolymer was prepared via controlled living anionic polymerization. Four copolymers, in terms of the molecular weights of the hydrogenated polybutadiene (HPB) and PMMA sequences (22,000–12,000, 63,300–31,700, 49,500–53,500, and 27,700–67,800), were used. We demonstrated with the stress–strain diagrams, in combination with scanning electron microscopy observations of deformed specimens, that the interfacial adhesion had a predominant role in determining the mechanism and extent of blend deformation. The debonding of PMMA particles from the LDPE matrix was clearly observed in the compatibilized blends in which the copolymer was not efficiently located at the interface. The best HPB‐b‐PMMA copolymer, resulting in the maximum improvement of the tensile properties of the compatibilized blend, had a PMMA sequence that was approximately half that of the HPB block. Because of the much higher interactions encountered in the PMMA phase in comparison with those in HPB (LDPE), a shorter sequence of PMMA (with respect to HPB but longer than the critical molecular weight for entanglement) was sufficient to favor a quantitative location of the copolymer at the LDPE/PMMA interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 22–34, 2005

Failure Envelope Curves in Polyethylene Solids

AbstractThe present work demonstrates that the failure envelope analysis can be applied for characterizing the ultimate tensile properties of polyethylene solids in which the inhomogeneous necking process is avoided. As a result, the ultimate properties are essentially identical to those of vulcanized rubbers above the glass transition temperature, suggesting that tie molecules connecting the fragmented lamellar clusters transmit the external led to the fracture site in the same manner as cross‐linked rubbers do. Consideration of this crystal‐network model may provide information about the molecular processes that lead to rupture. Furthermore, the present analytical method can possibly be developed for predicting rupture times when different types of tests, such as constant drawn, constant stress and constant rate of stress, are conducted.

The effects of SEBS- g-maleic anhydride reaction on the morphology and properties of polypropylene/PA6/SEBS ternary blends

Ternary blends, based on 70% by weight of polypropylene (PP) with 30% by weight of a dispersed phase, consisting of 15% polyamide-6 (PA6) and 15% of a mixture comprising varying ratios of an unreactive poly[styrene- b-(ethylene- co-butylene)- b-styrene] (SEBS) triblock copolymer and a reactive maleic anhydride-grafted SEBS- g-MA, were produced via melt blending in a co-rotating twin-screw extruder. TEM revealed the blend containing only non-reactive SEBS to exhibit individual PA6 and SEBS dispersed phases. However, the progressive replacement of SEBS with reactive SEBS- g-MA increased the degree of interfacial reaction between the SEBS and PA6 phases, thus reducing interfacial tension and providing a driving force for encapsulation of the PA6 by the SEBS. Consequently, the dispersed-phase morphology was observed to transform from two separate phases to acorn-type composite particles, then to individual core-shell particles and finally to agglomerates of the core-shell particles. The resultant blends exhibited significant morphology-induced variations in both thermal and mechanical properties. DSC showed that blends in which the diameter of the PA6 particles was reduced to ≤3 μm by the increasing interfacial reaction exhibited fractionated PA6 crystallisation. In general, mechanical testing showed the blends to exhibit inferior low-strain tensile properties (modulus and yield stress) compared to the matrix PP, but superior ultimate tensile properties (stress and strain at break) and impact strength. These changes are discussed with reference to composite models.

Effect of Monoazo Dye on The Mechanical Properties of Low Density Polyethylene and Unplasticised Polyvinyl Chloride

A red coloured monoazo dye (1-Phenylazo-2-naphthol) has been synthesized from aniline and 2-naphthol at a temperature of 5oC. UV spectrum of the dye showed the presence of azo group and naphthalene chromophores at wavelength of 285-400nm and 200nm respectively. The effect of the dye on the mechanical properties of UPVC film obtained by solvent casting and LDPE film obtained by compression moulding using standard hot melt compounding technique shows that the dye has no significant effect on the tensile properties of UPVC. However, addition of the dye to LDPE reduces the elongation – at – break, ultimate tensile strength and modulus properties. Journal of Applied Sciences and Environmental Management Vol. 7(2) 2003: 55-58

A study of the nanostructure and tensile properties of ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) has gained worldwide acceptance as a bearing material used in orthopaedic implants. Despite its widespread use, inherent properties of the polymer continue to limit the wear resistance and the clinical lifespan of implanted knee and hip prosthetics containing UHMWPE components. The degree of crystallinity of UHMWPE is known to strongly influence several of its tensile mechanical properties such as Young's modulus, yield stress, strain-hardening rates, work of fracture and ultimate tensile properties. In this study, medical grade UHMWPE was subjected to four different crystallization conditions resulting in UHMWPE with a range of crystalline morphologies. Thereafter, the crystalline nanostructure was quantitatively characterized using a combination of ultra-small angle X-ray scattering and differential scanning calorimetry. Low-voltage scanning electron microscopy was employed as a supplementary technique to compare the crystalline morphology resulting from each crystallization condition. In addition, uniaxial tensile tests were performed to assess the effects of crystallization conditions on the mechanical properties of UHMWPE. This study showed that while crystallization conditions strongly influenced the morphology of UHMWPE, in most cases the mechanical properties of the material were not significantly affected.

The effect of Ti alloying on the mechanical properties and microstructure of a Zn–Al–Cu–Mg alloy

Abstract The effect of Ti additions (0.01–0.20 wt.%) on the hardness, ultimate tensile strength, impact strength and creep properties of the gravity-cast Zn–Al–Cu–Mg alloy ZA-8 has been investigated. The Ti additions have no significant effect on the hardness. The ultimate tensile strength of the standard ZA-8 alloy has not been changed significantly with Ti additions up to 0.15 wt.% and then decreased with further increase in Ti content. The impact strength shows a maximum around 0.05–0.15 wt.% Ti. The lowest creep resistance is obtained at 0.01 wt.% Ti, and the highest value of creep resistance is reached for 0.20 wt.% Ti. Metallographic studies indicated that the addition of Ti has a profound effect on the microstructure. Also, Ti forms a complex-shaped intermetallic compound which was identified as TiZn15 by X-ray diffraction. It is suggested that the TiZn15 particles cause the increase in creep resistance and decrease in tensile strength.

Effect of crystallization conditions on spherulitic texture and tensile properties of sPS/PPO blends

AbstractIn the second study on melt‐miscible syndiotactic polystyrene (sPS) and poly(phenylene oxide) (PPO) blends, the effect of processing conditions on morphology, ultimate tensile properties, and the mode of fracture is reported. Bulk samples of the blends were molded and then crystallized from melt as well as from the quenched state at different temperatures. The spherulitic morphology of the melt‐crystallized blends, observed by scanning electron microscopy, revealed formation of complete, well‐developed spherulites whose texture increased in coarseness with increasing crystallization temperatures. In all the cold‐crystallized blends lamellar bundles formed a meshlike structure whose texture did not vary significantly with crystallization temperature. Depending on the crystallization temperature, 50/50 melt‐crystallized blends showed varying tensile properties and different modes of failure. In the samples with the largest amorphous domain size of 0.6 μm, the amorphous ellipsoids were cold drawn into fibrils during tensile loading and very high tensile strengths were recorded. The tensile properties for the other melt‐crystallized and all cold‐crystallized blends did not vary substantially with the changing crystallization temperature. The micrographs of the fractured surfaces of the melt‐crystallized blends suggested that, although intraspherulitic fracture occurred at low crystallization temperatures, interspherulitic fracture took place at high crystallization temperatures. The correlation of the morphology and mechanical properties suggests that melt‐miscible blends have good interfacial adhesion between phases and that, by varying composition and processing conditions, it might be possible to control amorphous domain sizes, which is critical in achieving better mechanical properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1984–1994, 2003

Ultimate tensile behavior of linear polyethylene solids

The influence of the elongation rate and temperature on the ultimate tensile properties of melt-crystallized linear polyethylene solids was investigated, with a double-edge-notched specimen to avoid necking, in which uniform deformation could be assumed throughout the experiment. The data on ultimate properties such as the tensile strength and elongation at break for different temperatures could be superimposed, by shifts along the elongation rate axis, to give a master curve as a function of the time to rupture. The shift factors obtained from the superpositioning of both the tensile strength and ultimate strain took the form of the Williams-Landel-Ferry equation. As a result, the ultimate data provided a failure envelope curve that made it possible to predict rupture times when the tensile tests were conducted under any experimental conditions.

Synthesis and compatibilization ability of hydrogenated polybutadiene- b-polyamide 6 diblock copolymer in low density polyethylene and polyamide 6 blends

This paper describes the synthesis of hydrogenated polybutadiene- b-polyamide 6 (HPB- b-PA6), a pure diblock copolymer, which consists of three main steps: synthesis of hydroxyl terminated polybutadiene, its hydrogenation and functionalization with an ϵ-caprolactam blocked diisocyanate. In a third step the functionalized HPB is copolymerized with ϵ-caprolactam monomer via ring opening anionic polymerization. The compatibilization ability of the synthesized pure diblock copolymer was evaluated in low-density polyethylene (LDPE)/polyamide 6 (PA6) blends. The investigation includes phase morphology development using both optical and electron scanning microscopy. The ultimate tensile properties of the modified and non-modified blends were also evaluated. The synthesized pure diblock copolymer exhibits very interesting interfacial activity both in terms of particle size reduction and improvement of the interfacial adhesion between the incompatible LDPE/PA6 phases. The tensile properties of the investigated blends were also significantly affected by the addition of the copolymer. The efficiency of compatibilization was found to be very sensitive to the molecular characteristics such as composition and molecular weight of the copolymer. Among the copolymers investigated a copolymer containing 24 wt% PA6 and having a total molecular weight M ̄ n of 87,000 was found to exhibit the most efficient interfacial activity.

Influence of thermal treatment on tensile failure of basalt fibers

In this contribution selected ultimate tensile properties of basalt fibers are presented. Properties are investigated after tempering to the 50, 100, 200, 300 °C. Scanning electron microscopy identifies structural changes of fibers. The distribution of stress at break is described by the Weibull type model. It was postulated that fracture occurs due to nonhomogeneities in fiber volume (probably near the small crystallites of minerals). The analysis of fibrous fragment evolved during abrasion of basalt weave is presented. Despite of fact that basalt particle are too thick to be respirable the handling of basalt fibers must be carried out with care.

Effect of block copolymers of various molecular architecture on the phase morphology and tensile properties of LDPE rich (LDPE/PS) blends

The emulsification efficiency of three different block copolymers consisting of hydrogenated polybutadiene (HPB) and polystyrene (PS), i.e. a pure diblock , a tapered diblock and a triblock copolymer has been compared in low density polyethylene/polystyrene (LDPE/PS) blends rich in polyethylene. The comparison relies upon the ability of these potential interfacial agents to stabilize fine phase dispersion and to promote good interfacial adhesion. Based on the phase morphology, the ultimate tensile properties and the dynamic viscosity of the modified blends, the tapered diblock copolymer is clearly the most efficient emulsifier. For instance a plateau is observed in the property-copolymer content dependence when 2 wt% tapered diblock are used compared to ca. 5 wt% in case of the pure diblock. In contrast, no plateau is observed when the triblock copolymer is used. This is assumed to result from a less quantitative localization of these two copolymers i.e. the pue diblock or the triblock at the LDPE/PS interface.

Acrylic-modified polyolefin ionomers as compatibilizers for poly(ethylene- co-vinyl alcohol)/aromatic copolyester blends

Polymeric alloys of poly(ethylene- co-vinyl alcohol) (EVOH) with an amorphous copolyester (PETG) were prepared using the sodium or the zinc ionomer of acrylic-modified polyolefin ionomers. Composition parameters examined were the main components ratio and at a fixed ratio the compatibilizer content. The techniques applied to assess compatibilization were: tensile testing, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and morphology examination of cryofractured surfaces using scanning electron microscopy (SEM). Both ultimate tensile properties and morphological features indicated that the ionomer, Na + is a more efficient compatibilizer, the amount required (ca 5 wt%) being 1/3 to that of the ionomer, Zn 2+. A plausible explanation for this finding is proposed. Analysis of DMA moduli data supports the view that films obtained are laminar in structure — a significant result for film barrier applications.

Polystyrene/wood composites and hydrophobic wood coatings from water-based hydrophilic-hydrophobic block copolymers

The combination of synthetic thermoplastic polymers and wood is normally problematic because wood surfaces are hydrophilic while typical thermoplastic polymers are hydrophobic. A possible solution is to use block copolymer coupling agents. In this work we show the use of a potentially useful synthetic method of producing hydrophilic-hydrophobic block copolymers as hydrophobic coatings and coupling agents in polystyrene/ wood flour composites. In particular, wood veneers are coated with water-based emulsions of hydrophilic-hydro- phobic block copolymers from styrene and methacrylic acid. Dried coated surfaces are shown to become hydro- phobic through dynamic contact angle measurements. When wood flour is coated with the hydrophilic-hydro- phobic block copolymer based on styrene and acrylic acid, significant improvement in the ultimate tensile properties of composites formed from coated wood flour/ polystyrene mixtures is realized. Since no volatile organic compounds (VOCs) are used in coating wood surfaces and subsequent composite production, improvement in mechanical properties of thermoplastic/wood flour composites are shown to occur in environmentally responsible formulations.

Single Fiber Strength Variations of Developing Cotton Fibers: Among Ovule Locations and Along the Fiber Length

This paper, the first in a series on variations in single fiber properties of developing and mature cotton, focuses on single fiber tensile property variations of greenhouse-grown developing G. hirsutum (Maxxa variety). Variations along single fibers and among locations on ovules are examined on developing and mature cotton fibers sampled from ovules located in the middle of the locules of the first-position bolls. The breaking force and elongation of the midsection of the fibers from the medial portion of these ovules, in either hydrated or dried state fibers, show the most significant increases during the fourth week of development. As fibers develop beyond 30 dpa, the single fiber breaking forces, linear densities, and tenacities become scattered. The forces required to break the mid- sections of the single fibers are highest, while the breaking forces for fiber sections closer to the basal or tips are similarly lower at all stages of development. Fibers from the medial sections of the ovules have the highest tenacities, followed by those from the micropylar and chalazal ends. Of the mature fibers, the ribbon widths of fibers from the medial sections and the micropylar ends of the ovules are similar, but the medial sections are higher than the micropylar ends. Fibers from the chalazal ends are narrowest and have the lowest linear densities. The tenacities of single fibers from the medial regions of the ovules are higher than those from the chalazal and micropylar ends, the latter two being similar. Ultimate fiber tensile properties are reached in the developing fibers by 30 dpa; further fiber development contributes to thicker cell walls and thus to fiber mass, but not to intrinsic fiber strength.

Synthesis and bulk properties of poly(methyl methacrylate)-b-poly(isooctyl acrylate)-b-poly(methyl methacrylate)

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(isooctylacrylate) (PIOA)-b-PMMA triblock copolymers (MIM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA)-b-PMMA precursors (MTM) by isooctyl alcohol. Phase separation is observed for all the investigated triblock copolymers, thus containing PMMA outer blocks in the 3500–50,000 molecular weight (MW) range and PIOA inner block with MW in the 100,000–300,000 range. The ultimate tensile properties of these MIM triblock copolymers are poor even when PMMA blocks of 50,000MW are associated with an inner PIOA block of 300,000MW. A reasonable explanation should be found in the molecular weight between chain entanglements (Me), which has been estimated at 60,000 for PIOA, much higher than Me for the traditional polydiene central blocks in the well-known thermoplastic elastomers of the triblock type. The tensile behavior of MIM copolymers has been successfully accounted for by a simple elastomer model free from chain entanglements, supporting the view that the lack of entanglements in the central block is very detrimental to the mechanical properties of the investigated fully (meth)acrylate triblock copolymers.

Synthesis of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblocks and their potential as thermoplastic elastomers

A series of well defined poly(methyl methacrylate) (PMMA)-b-poly(n-butyl acrylate) (PnBA)-b-PMMA triblock copolymers (MnBM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA)-b-PMMA precursors (MTM) by n-butanol. Phase separation is observed for all the investigated triblock copolymers, which contain PMMA outer blocks in the 5000–50 000 molecular weight (MW) range and PnBA inner blocks with MW in the 100 000–200 000 range. Although the ultimate tensile properties of these MnBM triblock copolymers are poor compared to traditional diene-based TPEs (SBS and SIS), they are much better than those ones reported for PMMA-b-poly(isooctyl acrylate) (PIOA)-b-PMMA triblocks (MIM). A reasonable explanation for this observation is found in the average molecular weight between chain entanglements (Me) that has been estimated to be 28 000 for the central PnBA rubbery block, which is consistently much smaller than for PIOA (59 000) and substantially higher than Me for polybutadiene (1700) and polyisoprene (6100). The tensile behavior of MnBM copolymers cannot be fitted by either a simple elastomer model free from chain entanglements (suitable to MIM) or by a “filler” modified rubber model (suitable for diene-based TPEs), supporting the hypothesis that the mechanical properties of the investigated (meth)acrylate thermoplastic elastomers are significantly affected by any change in Me of the central acrylate block. Viscoelastic analysis shows that MnBM triblocks are of higher complex viscosity than the SBS and SIS analogs, leading to a shift in the order–disorder transition temperature to much higher temperature, unless the outer PMMA blocks are of very low molecular weight (5000).

Thermal crosslinking of poly(methyl methacrylate) by reaction of methyl ester and quaternary ammonium salt and application to (meth)acrylate-based TPEs

Copolymers of N-vinylbenzyl N-methyl pyrrolidinium chloride (VBMPC) and methyl methacrylate, PVBMPC-co-poly(methyl methacrylate) (PMMA), were synthesized by free-radical copolymerization and proved to be prone to crosslinking as a result of the reaction of methyl ester groups with benzyl methyl pyrrolidinium chloride (BMPC) moieties at temperatures higher than 110 °C. When the VBMPC content was lower than 20 wt %, these copolymers were miscible with homo-PMMA. Blends of homo-PMMA and PVBMPC-co-PMMA fully could be cured above 150 °C, when the molecular weight of PMMA exceeded 10,000 and the VBMPC content of the copolymer was higher than 5 wt %. This reaction was carried out to crosslink selectively the PMMA microdomains of PMMA-b-poly(isooctyl acrylate) (PIOA)-b-PMMA (MIM) triblock copolymers to explain the mechanism for the mechanical failure of fully (meth)acrylic thermoplastic elastomers. Comparison of the ultimate tensile properties of MIM block copolymers, when the dispersed PMMA phases and PIOA matrix were crosslinked, led to the conclusion that the ductile failure of the hard PMMA microdomains rather than the elastic failure of the PIOA matrix was the reason for the mechanical failure of MIM triblocks. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4402–4411, 1999

Polyurethane/HDPE blends: 2. Compatibilization with an olefinic ionomer

The compatibility of melt-mixed blends of a partially neutralized poly(ethylene-co-methacrylic acid-co-isobutyl acrylate) Zn2+ ionomer with a polyester-type polyurethane (PU), reported in Part 1 of this work, allowed application of the ionomer as a compatibilizer for incompatible PU/high-density polyethylene (HDPE) blends. The techniques applied were dynamic mechanical analysis (d.m.a.), tensile testing, differential scanning calorimetry and scanning electron microscopy (SEM) of cryofractured surfaces. Once optimization of mixing conditions was established, various composition parameters were examined such as PU/HDPE ratio and compatibilizer content. Blend performance was assessed by means of tensile testing and d.m.a., while morphology was studied mainly by SEM and indirectly by large- and small-deformation behaviour. Although all ternaries studied at ionomer contents of ca. 15wt% had a satisfactory level of ultimate tensile properties, the PU-rich polymeric alloys performed best.

Polyurethanes from Alcell® lignin fractions obtained by sequential solvent extraction

Lignin-derived polyurethane films were synthesized by solution casting using three fractions of distinct molecular weight and chemical functionality from Alcell® lignin. A three-component system of lignin fraction, polyethylene glycol (PEG) of MW=400 g mol −1 and polymeric methyl-diisocyanate (MDI) was used. For each lignin fraction, the effects of varying the NCO/OH ratio and lignin content on the crosslink density, ultimate tensile properties and dielectric strength of the polyurethanes were studied. The crosslink density was found to increase with molecular weight of lignin. Strong polyurethanes were produced with the high molecular weight fraction of Alcell® lignin, but the polyurethanes from the medium molecular weight fraction appeared to be tougher and more flexible. For both the medium and high molecular weight fractions of Alcell® lignin used, polyurethanes produced with lignin contents above 35 wt% were found to be too brittle and glassy to be tested. A maximum of 18 wt% of the low molecular weight lignin fraction could be used to prepare polyurethanes. Any higher compositions attempted produced polyurethanes which were too brittle to be tested. For all three fractions, the dielectric constant of the polyurethanes, decreased with increasing lignin content or NCO/OH ratio.