High Molecular Mass Polyethylene Research Articles

Destressing Yeast for Higher Biofuel Yields: Can Excess Chaotropicity Be Mitigated?

Biofuels have the capacity to contribute to carbon dioxide emission reduction and to energy security as oil reserves diminish and/or become concentrated in politically unstable regions. However, challenges exist in obtaining the maximum yield from industrial fermentations. One challenge arises from the nature of alcohols. These compounds are chaotropic (i.e. causes disorder in the system) which causes stress in the microbes producing the biofuel. Brewer's yeast (Saccharomyces cerevisiae) typically cannot grow at ethanol concentration much above 17% (v/v). Mitigation of these properties has the potential to increase yield. Previously, we have explored the effects of chaotropes on model enzyme systems and attempted (largely unsuccessfully) to offset these effects by kosmotropes (compounds which increase the order of the system, i.e. the "opposite" of chaotropes). Here we present some theoretical results which suggest that high molecular mass polyethylene glycols may be the most effective kosmotropic additives in terms of both efficacy and cost. The assumptions and limitations of these calculations are also presented. A deeper understanding of the effects of chaotropes on biofuel-producing microbes is likely to inform improvements in bioethanol yields and enable more rational approaches to the "neutralisation" of chaotropicity.

Development and evaluation of 3D knitted fabrics to protect against mechanical risk

In this research, eight different 3D weft-knitted fabrics were developed and evaluated. 3D fabrics have been knitted on circular weft-knitting machines with two different gauges: 20E gauge and 28E gauge. Three different raw materials were used for the fabric’s production: high molecular mass polyethylene (HPPE) yarn and 0.05 mm diameter steel wire in the outer layers (for the front and reverse) and polyamide yarn in the binding layer. The experiments were conducted on the developed 3D knitted fabrics to determine the fabric’s resistance to mechanical risks such as circular blade cut, puncture, abrasion, and also to evaluate the comfort parameter, such as air permeability. It was defined that 3D weft-knitted fabrics best results on tests: circular blade cut, puncture and abrasion resistant were achieved using HPPE yarn twisted with steel wire, higher mass per unit area with more significant amount of steel wire. According to the standard EN 388:2003, three samples of developed 3D weft-knitted fabrics had the highest 5th blade cut and the highest (4th) abrasion resistance level. All of them had the highest (4th) level of puncture resistance. 3D fabrics knitted on a circular weft-knitting machine of gauge 28E ensured 1.3–2.1 times greater blade cut and 4.9–12.1 times greater abrasion resistance result, than fabrics knitted on gauge 20E, due to a higher stitch density, higher mass per unit area, density and fabric’s thickness. But on the other hand, these parameters lowered air permeability by 20.2–43.0%.

The 2D Structure of the T. brucei Preedited RPS12 mRNA Is Not Affected by Macromolecular Crowding.

Mitochondrial transcript maturation in African trypanosomes requires RNA editing to convert sequence-deficient pre-mRNAs into translatable mRNAs. The different pre-mRNAs have been shown to adopt highly stable 2D folds; however, it is not known whether these structures resemble the in vivo folds given the extreme “crowding” conditions within the mitochondrion. Here, we analyze the effects of macromolecular crowding on the structure of the mitochondrial RPS12 pre-mRNA. We use high molecular mass polyethylene glycol as a macromolecular cosolute and monitor the structure of the RNA globally and with nucleotide resolution. We demonstrate that crowding has no impact on the 2D fold and we conclude that the MFE structure in dilute solvent conditions represents a good proxy for the folding of the pre-mRNA in its mitochondrial solvent context.

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

Assembly of functional gold nanoparticle on silica microsphere

We demonstrate a controlled synthesis of silica microsphere with the surface-decorated functional gold nanoparticles. Surface of silica microsphere was modified by 3-aminopropypltriethoxysilane and 3-aminopropyldimethylethoxysilane to generate a positive electric field, by which the gold nanoparticles with the negative charges (unconjugated, thiolated polyethylene glycol functionalized with the traceable packing density and conformation) were able to be attracted to the silica microsphere. Results show that both the molecular conjugation on gold nanoparticle and the uniformity in the amino-silanization of silica microsphere influenced the loading and the homogeneity of gold nanoparticles on silica microsphere. The 3-aminopropyldimethylethoxysilane-functionalized silica microsphere provided an uniform field to attract gold nanoparticles. Increasing the ethanol content in aminosilane solution significantly improved the homogeneity and the loading of gold nanoparticles on the surface of silica microsphere. For the gold nanoparticle, increasing the molecular mass of polyethylene glycol yielded a greater homogeneity but a lower loading on silica microsphere. Bovine serum albumin induced the desorption of gold nanoparticles from silica microsphere, where the extent of desorption was suppressed by the presence of high-molecular mass polyethylene glycol on gold nanoparticles. This work provides the fundamental understanding for the synthesis of gold nanoparticle-silica microsphere constructs useful to the applications in chemo-radioactive therapeutics.

Effects of ball burnishing on surface properties of low density polyethylene

We have end milled surfaces and then applied ball burnishing to specimens of low density high molecular mass polyethylene (LDPE). An important objective was roughness minimization. For selected ball diameters, the influence of burnishing parameters such as force F and burnishing speed f on selected surface geometry parameters has been determined: roughness Ra, total height of the profile Rt, and also the two-dimensional roughness change KRa. We find the minimum value of Ra=0.57µm and the maximum value of KRa=5.1, both highly desired results. In the best case, Rt has decreased from 14.5µm to 4.0µm. Microhardness values, ball-on-disc wear values and scratch resistance testing all show property improvement of milled and burnished surfaces as compared to surfaces milled only. Burnishing decreases the wear rate by 58%.

Experimental understanding of the viscosity reduction ability of TLCPs with different PEs

In this study, two thermotropic liquid crystalline polyesters (TLCPs) synthesized by polycondensation of phydroxybenzoic acid /hydroquinone/ poly dicarboxylic acid were used as viscosity reduction agents for polyethylene (PE). The TLCPs had different thermal, rheological and other physical properties that were quantitatively characterized. The two TLCPs were blended with high density PE (HDPE) and high molecular mass PE (HMMPE) by simple twin screw extrusion under the same weight ratio of 1.0 wt% and were each rheologically characterized at 190 o C. The TLCPs acted as processing modifiers for the PEs and the bulk viscosity of the blends decreased dramatically. However, the viscosity reduction ability was not identical: one TLCP had obviously higher viscosity reduction ability on the HDPE, with a maximum viscosity reduction ratio of 68.1%, whereas the other TLCP had higher viscosity reduction ability on the HMMPE, with a maximum viscosity reduction ratio of 98.7%. Proposed explanations for these differences are evaluated.

Size effect of cubic ZrO2 nanoparticles on ionic conductivity of polyethylene oxide-based composite

A solvent free solid composite polymer electrolyte (SCPE) film consisting of high molecular mass polyethylene oxide (PEO) with sodium perchlorate (NaClO4) as electrolytic salt and cubic zirconium oxide (ZrO2) nanoparticles as the filler has been prepared by solution casting technique to influence the transport properties. X-ray diffraction and Fourier transform infrared spectroscopy confirm the formation of the SCPE film, whereas atomic force microscopy reveals the presence of a network of interconnected nanoparticles forming uniform surface feature of relatively low roughness. The highest ionic conductivity (σ = 6.96 × 10-5 S-cm-1) for PEO25 - NaClO4 with 5 wt. % ZrO2 nanoparticles of the smallest size 4.5 nm is an order of magnitude higher than the pure PEO25 - NaClO4 at room temperature. The conductivity enhancement is due to the creation of additional sites and favorable conduction pathways for ionic transport through Lewis acid-base type interactions between the polar surface groups of the ceramic filler and the electrolyte ionic species.

A comparative study of thermotropic LCP and organoclay as fillers in high molecular mass polyethylene with different blending sequences

AbstractThe influences of thermotropic liquid crystalline copolyester (TLCP) on viscosity reduction in high molecular mass polyethylene (HMMPE) filled with organoclay were investigated by controlling the blending sequence. The interactions between organoclay and TLCP in HMMPE create different morphologies and influence rheological properties of the clay/TLCP/HMMPE blends. When the organoclay was blended with TLCP first, large amounts of organoclay formed partially intercalated structures in TLCP, with phase separation occurring at the temperature when TLCP was in the nematic phase, corresponding an antagonistic effect which weakens viscosity reduction ability of TLCP for HMMPE. However, with first blending of TLCP with HMMPE and then adding organoclay into the blend, most of the organoclay enriched on TLCP surfaces in the blend. Such interaction prevents TLCP droplets from coalescing at high shear stresses, enlarging the processing window. A phenomenological model, originally for HMMPE/TLCP systems, was successfully adopted to predict the flow behaviors of clay/HMMPE/TLCP blends. POLYM. ENG. SCI., 50:1679–1688, 2010. © 2010 Society of Plastics Engineers

Organoclay-modified thermotropic liquid crystalline polymers as viscosity reduction agents for high molecular mass polyethylene

Small amounts of organoclays of different sizes and concentrations were added into thermotropic liquid crystalline polymer (TLCP) forming four types of organoclay-modified TLCPs (TC3 white, TC3 dark, TC3 FS, and TC3 UP), which had different rheological behaviors in the nematic temperature region of TLCP. Acting as viscosity reduction agents, 1.0 wt% of each organoclay-modified TLCPs were blended with high molecular mass polyethylene (HMMPE), respectively. The organoclay-modified TLCP/HMMPE blends displayed different rheological properties from each other or compared with HMMPE and 1.0 wt% TLCP/HMMPE blend [PT1]. The organoclay-modified TLCPs had greater viscosity reduction efficiency than the original TLCP in HMMPE, a lower yielding stress and yielding start shear rate, and a narrower yielding transition region than those of PT1. The rheological performance of the blends, 1.0 wt% TC3 white/HMMPE, 1.0 wt% TC3 FS/HMMPE, and PT1, could be successfully described by a binary flow pattern model.

Organoclay/thermotropic liquid crystalline polymer nanocomposites. Part IV: organoclay of comparable size to fully extended TLCP molecules

Organoclay with a size of 100–200 nm was successfully prepared by a combination of wet ball milling and ultrasonication methods without changing its physico-chemical properties. A nanocomposite (TC3 FS) of 3.0 wt% treated organoclay in thermotropic liquid crystalline polymer (TLCP) was prepared. The treated organoclay was of comparable size to the fully extended TLCP molecules and it formed weak interactions with them. The liquid crystallinity of the TLCP was not greatly affected by the treated organoclay at the nematic temperature of the TLCP. Rheological characterization demonstrated that the viscosity of the TC3 FS was less than one order of magnitude higher than that of the TLCP in the linear viscoelastic region, and the steady shear viscosity of the two materials was comparable in steady shear experiments. Thus, TC3 FS is a promising viscosity reduction agent for high molecular mass polyethylene (HMMPE), functioning similarly to TLCP. The 1.0 wt% TC3 FS in HMMPE has more efficient viscosity reduction ability than the 1.0 wt% TLCP in HMMPE, with lower yielding stress and yield-starting shear rate, as well as a narrower yield shear rate region. The viscosity reduction ability of the TLCP was enhanced by the treated organoclay.

Experimental measurement and numerical simulation of viscosity reduction effects in HMMPE containing a small amount of exfoliated organoclay-modified TLCP composite

A small amount (1 wt%) of organoclay-modified thermotropic liquid crystalline polymer (TLCP) acting as a viscosity reduction agent in high molecular mass polyethylene (HMMPE) was characterized and compared with purified TLCP (1 wt%) in HMMPE at 190 °C and 230 °C, respectively, where the TLCP displayed nematic and nematic-isotropic biphase structures. In the TLCP/PE blend at 190 °C and 230 °C, dramatic reductions in viscosity were observed with significant improvement in extrudate surface smoothness and an enlarged processing window. For the organoclay-modified TLCP in PE, the viscosity reduction ability of TLCP was further enhanced with viscosity dropped by up to >98.5% and >97.4% at 190 °C and 230 °C and processing window enlarged to >700 s −1 and >900 s −1 respectively in comparison to that of PE. Moreover, yielding stress, initial transition shear rate and transition region decreased to lower magnitudes than those of the TLCP/PE blend. A phenomenological model was applied to elucidate the mechanism of organoclay, TLCP and PE conformation before and after yielding in the confined capillary environment. A binary flow pattern model was applied to successfully predict the rheological behavior of the blends at 190 °C.

Effects of thermotropic LCP on rheologica behavior of high molecular mass polyethylene/organoclay composites

A thermotropic liquid crystalline polymer (TLCP) based on hydroxybenzoic acid, hydroquinone and sebacic acid was used as a processing aid in the extrusion of high molecular mass polyethylene (HMMPE)/clay nanocomposites. Clay/TLCP with optimal mass ratio loading in HMMPE matrix has better thermal stability than that of clay or TLCP blends. Capillary rheometry experiments were carried out at processing temperature 190 °C with TLCP in the full nematic phase. TLCP is an effective processing aid agent with viscosity reduction in excess of 95%. The mechanism is proposed and analyzed by morphological study and surface analysis. TLCP has been shown to act as both a compatiblizer between nanoclay and the HMMPE matrix and a processing aid for the nanocomposite.

Shear-induced interactions in blends of HMMPE containing a small amount of thermotropic copolyester HBA/HQ/SA

Shear-induced interactions between high molecular mass polyethylene (HMMPE) melt and a thermotropic liquid crystalline copolyester, HBA/HQ/SA (TLCP) were investigated using large amplitude oscillatory shear and capillary shear. Polarized optical microscopy (POM) observations show that the mono-domain nematic TLCP droplets embedded inside a HMMPE melt may be readily elongated using large amplitude oscillatory shear. The HMMPE melt adjacent to the elongated TLCP filament was observed to crystallize faster than that in the matrix away from the interface. TEM analysis on the 1 wt% TLCP/HMMPE blend quenched after capillary shear shows that there are strong interfacial interactions between the elongated TLCP filament and the HMMPE matrix. Long range PE lamellae orientational order up to 2 μm away from the TLCP filament surface were observed, with all the lamellae surface normal parallel to the TLCP fiber. Additionally, a strong interfacial compatibility between the TLCP filament and the HMMPE matrix with an interfacial thickness of ∼30 nm has also been observed. The enhanced interfacial compatibility is attributed to the –CH 2– group interactions due to chain alignment in both components at their interface. These results provide a fundamental insight to other TLCP containing thermoplastics where compatibilities may be present due to segmental interactions.

A phenomenological model for the viscosity reductions in blends of HMMPE containing a small quantity of thermotropic liquid crystalline copolyester HBA/HQ/SA

In this paper, we present a phenomenological model for the viscosity changes in bulk high molecular mass polyethylene (HMMPE) due to the addition of a very small quantity of a main chain longitudinal thermotropic liquid crystalline polymer (TLCP) containing flexible spacers. The chain alignment in the elongated TLCP domains causes chain alignment and disengagement in the neighboring HMMPE melt. In converging capillary flows, this occurs at a certain critical centerline velocity. After the onset of such transition, melt of elongated chain conformations forms from the center core and expands towards the capillary wall with increasing flow rates. The model successfully predicts both the drastic viscosity reduction effects and the critical yield stress in the HMMPE+TLCP blends without any adjustable parameters. Our model is also applicable to other systems that undergo flow-induced phase transitions, e.g. in biphasic liquid crystalline polymer melts.

A solvent-free composite polymer/inorganic oxide electrolyte for high efficiency solid-state dye-sensitized solar cells

A new solvent-free composite polymer electrolyte consisting of high-molecular mass polyethylene oxide (PEO) filled with titanium oxide and containing LiI and I 2 was developed. The introduction of the inorganic filler (TiO 2 Degussa P25) into the polymer matrix produces dramatic morphological changes to the host polymer structure. Upon addition of the inorganic oxide, the surface roughness increases, with respect to the original polymer and in parallel, the fractal dimension decreases. Both the thermograms and the atomic force microscope (AFM) pictures confirm the amorphicity of the composite electrolyte. The polymer sub-units are held together in a parallel orientation, forming straight long chains of about 500 nm in width, along which TiO 2 spherical particles of about 20–25 nm in diameter are distributed. The polymer chains separated by the titania particles are arranged in a three-dimensional, mechanically stable network, that creates free space and voids into which the iodide/triodide anions can easily migrate. All solid-state dye-sensitized solar cells fabricated using this composite electrolyte present high efficiencies (typical maximum incident photon to current efficiency (IPCE) as high as 40% at 520 nm and overall conversion efficiency ( η) of 0.96% ( V oc=0.67 V, J sc=2.050 mA/cm 2, FF=39%)) under direct solar irradiation. Further improvement of the photovoltaic performance is expected by optimization of the electrolyte parameters and of the cell assembly.

Study of the ethylene polymerization over homogeneous and supported catalysts based on 2,6-bis(imino)pyridyl complexes of Fe(II) and Co(II)

The kinetic data on ethylene polymerization over homogeneous catalysts based on 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridineiron(II) and cobalt(II) chlorides (LMCl 2, M = Fe, Co) with different aluminium-organic activators (MAO, AlMe 3, Al( i-Bu) 3) are reported. LFeCl 2 is very effective with AlMe 3 and Al( i-Bu) 3 as activator and LCoCl 2 is highly active in the presence of AlMe 3. For MAO as activator, the activity depends on the content of free AlMe 3 in MAO. Maximal activity has been found for MAO completely purified from free AlMe 3. According to 1 H and 2 H NMR study, formation of the similar neutral intermediates of the type [LFe(II)Me(μ-Me) 2AlMe 2] have been detected for LFeCl 2/AlMe 3 and LFeCl 2/MAO catalysts. In the system LCoCl 2/MAO, the complex of the type LCo(II)Me(X)·MAO (X = Me or Cl) with terminal Co–Me group is detected. Interaction of LCoCl 2 with AlMe 3 results in the formation of diamagnetic Co(I) species. Highly active supported catalysts SiO 2/LFeCl 2+AlR 3 and SiO 2/MAO/LFeCl 2 have been prepared. In contrast to homogeneous systems, the supported catalysts are stable at elevated temperatures of polymerization (70 °C) and produce high molecular mass polyethylene with improved morphology.

Antigene effect in K562 cells of a PEG-conjugated triplex-forming oligonucleotide targeted to the bcr/abl oncogene.

Triplex-forming oligonucleotides are able to modulate gene expression by site-specific binding to genomic DNA. Their use as therapeutic agents is limited by inefficient cellular uptake, scarce nuclear internalization, and oligonucleotide self-aggregation. In this study, we demonstrate that a 13-mer AG motif oligonucleotide covalently linked to a high-molecular mass (9000 Da) polyethylene glycol (PEG ODN(13)) exhibits uptake and biological properties that are superior to those of the nonconjugated isosequence analogue (free ODN(13)). Band-shift and footprinting experiments showed that PEG ODN(13) forms a stable triple helix (apparent K(d) between 10(-6) and 10(-7) M in 50 mM Tris-acetate, 10 mM MgCl(2), pH 7.4, 37 degrees C) with a natural polypurine-polypyrimidine target located in the 5' flanking region of the human bcr/abl oncogene. Confocal laser microscopy performed on unfixed live cells stained with hexidium iodide as well as on glass-fixed cells stained with propidium iodide showed that fluorescein-labeled PEG ODN(13) is far more efficiently taken up and internalized in the nucleus by K562 and HeLa cells than the nonconjugated free ODN(13). It was found that PEG ODN(13) specifically downregulated the transcription of bcr/abl mRNA at 65 +/- 5% with respect to control and inhibited cell growth by 32 +/- 3% in a 3 day liquid culture assay. Moreover, PEG ODN(13) was more resistant against S1 and fetal bovine serum nucleases than free ODN(13), and less inclined to self-associate into multistrand structures in solution. Taken together, these results provide useful elements for designing artificial transcription repressors with enhanced potency in vivo.

Phase separation of polyethylene oxide (PEO)–water solution and its relationship to the flocculating capability of the PEO

The phase separation of a dilute aqueous high molecular mass polyethylene oxide (PEO) solution was studied by viscosity measurements as a function of temperature. Upon phase separation, the PEO–water system exhibited drastic changes in its rheological behavior. Above a certain temperature, the viscosity of the PEO solution did not decrease with increasing temperature but instead remained constant. This certain temperature corresponded to the cloud point temperature (CPT) of the PEO–water system. By increasing the level of shear, the CPT was shifted to lower levels. The degree of suppression was found to depend on the PEO and Na 2SO 4 concentrations. Aggregation of phase-separated PEO was studied by particle size measurements using the laser diffraction technique. During the aggregation, the PEO aggregates reached an equilibrium size. Deviation of the system temperature from the CPT was found to be the driving force for the aggregation process. The enhancement in the flocculation of clay particles by PEO upon phase separation was demonstrated. With increasing deviation from the CPT, the flocculation was faster and with a larger equilibrium floc size.