Comparison of Thermal Decomposition of Polystyrene Products vs. Bio-Based Polymer Aerogels

Samples of polystyrene (PS), extended polystyrene foam (EPS foam), and 3 bio-based foam-like polymer/clay aerogels were produced, and examined under pyrolysis conditions. The polystyrene products produced pyrolysis products including toluene, styrene, benzaldehyde, and 4-phenyl-1-butyne; all consistent with previous reports. These highly flammable volatiles would be further expected to combust under flame conditions, producing carbon monoxide and carbon dioxide; prior work suggests that carbon monoxide poses the greatest health risk from the burning of both polystyrene and EPS. Pectin and alginate carbohydrate polymer aerogels, subjected to the same pyrolysis conditions as the polystyrene materials, produced products which were generally consistent with prior literature, and presented only moderate known health risks (similar to those of the EPS pyrolysis). As with PS and EPS foams, the alginate and pectin aerogel by-products are flammable, and are expected to be converted to carbon oxides. Casein, a milk-derived protein, generated organic nitriles and aromatic compounds under pyrolysis conditions, again consistent with literature for proteins in general. While none of the bio-based pyrolysis products of this study pose known significant health risks, it is possible that some of nitriles could be converted to hydrogen cyanide, leading to the recommendation that such protein-based products be further investigated prior to implementation in consumer/civil engineering applications

The relation between the rheological properties of gels and the mechanical properties of their corresponding aerogels

A series of low density, highly porous clay/poly(vinyl alcohol) composite aerogels, incorporating ammonium alginate, were fabricated via a convenient and eco-friendly freeze drying method. It is significant to understand rheological properties of precursor gels because they directly affect the form of aerogels and their processing behaviors. The introduction of ammonium alginate impacted the rheological properties of colloidal gels and improved the mechanical performance of the subject aerogels. The specific compositions and processing conditions applied to those colloidal gel systems brought about different aerogel morphologies, which in turn translated into the observed mechanical properties. The bridge between gel rheologies and aerogel structures are established in the present workPostprint (published version

TEG® and RapidTEG® are unreliable for detecting warfarin-coagulopathy: a prospective cohort study

BACKGROUND: Thromboelastography® (TEG) utilizes kaolin, an intrinsic pathway activator, to assess clotting function. Recent published studies suggest that TEG results are commonly normal in patients receiving warfarin, despite an increased International Normalized Ratio (INR). Because RapidTEG™ includes tissue factor, an extrinsic pathway activator, as well as kaolin, we hypothesized that RapidTEG would be more sensitive in detecting a warfarin-effect. METHODS: Included in this prospective study were 22 consecutive patients undergoing elective cardioversion and receiving warfarin. Prior to cardioversion, blood was collected to assess INR, Prothrombin Time, TEG, and RapidTEG. RESULTS: INR Results: 2.8 ± 0.5 (1.6 to 4.2). Prothrombin Time Results: 19.1 ± 2.2 (13.9. to 24.3). TEG Results (Reference Range): R-Time: 8.3 ± 2.7 (2–8); K-Time: 2.1 ± 1.4 (1–3); Angle: 62.5 ± 10.3 (55–78); MA: 63.2 ± 10.3 (51–69); G: 9.4 ± 3.5 (4.6-10.9); R-Time within normal range: 10 (45.5%) with INR 2.9 ± 0.3; Correlation coefficients for INR and each of the 5 TEG variables were insignificant (P > 0.05). RapidTEG Results (Reference Range): ACT: 132 ± 58 (86–118); K-Time: 1.2 ± 0.5 (1–2); Angle: 75.4 ± 5.2 (64–80); MA: 63.4 ± 5.1 (52–71); G: 8.9 ± 2.0 (5.0-11.6); ACT within normal range: 9 (40.9%) with INR 2.7 ± 0.5; Correlation coefficients for INR and each of the 5 RapidTEG variables were insignificant (P > 0.05). CONCLUSIONS: TEG, using kaolin activation, and RapidTEG, with kaolin and tissue factor activation, were normal in a substantial percent of warfarin patients, despite an increased INR. The false-negative rate for detecting warfarin coagulopathy with either test is unacceptable. The lack of correlation between INR and all TEG and RapidTEG components further indicates that these methodologies are insensitive to warfarin effects. Findings suggest that intrinsic pathway activation may mitigate detection of an extrinsic pathway coagulopathy

In vitro analysis of the effects on wound healing of high- and low-molecular weight chains of hyaluronan and their hybrid H-HA/L-HA complexes

Abstract Background: Recent studies have reported the roles of Hyaluronic acid (HA) chains of diverse length in wound repair, especially considering the simultaneous occurrence in vivo of both high- (H-HA) and low-molecular weight (L-HA) hyaluronan at an injury site. It has been shown that HA fragments (5 ≤ MW ≤ 20 kDa) usually trigger an inflammatory response that, on one hand, is the first signal in the activation of a repair mechanism but on the other, when it’s overexpressed, it may promote unwanted side effects. The present experimental research has aimed to investigate H-HA, L-HA and of a newly developed complex of the two (H-HA/L-HA) for stability (e.g. hyaluronidases digestion), for their ability to promote wound healing of human keratinocytes in vitro and for their effect on cellular biomarker expression trends. Results: Time-lapse video microscopy studies proved that the diverse HA was capable of restoring the monolayer integrity of HaCat. The H-HA/L-HA complex (0.1 and 1%w/v) proved faster in regeneration also in co-culture scratch test where wound closure was achieved in half the time of H-HA stimulated cells and 2.5-fold faster than the control. Gene expression was evaluated for transformation growth factor beta 1 (TGF-β1) proving that L-HA alone increased its expression at 4 h followed by restoration of similar trends for all the stimuli. Depending on the diverse stimulation (H-HA, L-HA or the complex), metalloproteinases (MMP-2, -9, -13) were also modulated differently. Furthermore, type I collagen expression and production were evaluated. Compared to the others, persistence of a significant higher expression level at 24 h for the H-HA/L-HA complex was found. Conclusions: The outcomes of this research showed that, both at high and low concentrations, hybrid complexes proved to perform better than HA alone thus suggesting their potential as medical devices in aesthetic and regenerative medicine. Keywords: Wound healing, Hyaluronan, MMPs, Hybrid complexe

Biomolecules as Flame Retardant Additives for Polymers: A Review

Biological molecules can be obtained from natural sources or from commercial waste streams and can serve as effective feedstocks for a wide range of polymer products. From foams to epoxies and composites to bulk plastics, biomolecules show processability, thermal stability, and mechanical adaptations to fulfill current material requirements. This paper summarizes the known bio-sourced (or bio-derived), environmentally safe, thermo-oxidative, and flame retardant (BEST-FR) additives from animal tissues, plant fibers, food waste, and other natural resources. The flammability, flame retardance, and—where available—effects on polymer matrix’s mechanical properties of these materials will be presented. Their method of incorporation into the matrix, and the matrices for which the BEST-FR should be applicable will also be made known if reported. Lastly, a review on terminology and testing methodology is provided with comments on future developments in the field

Sustainable, Low Flammability, Mechanically-Strong Poly(vinyl alcohol) Aerogels

Poly(vinyl alcohol) (PVA), tannic acid (TA) and sodium hydroxide (NaOH) were used to prepare low-flammability, mechanically-strong aerogels via an environmentally-friendly freeze-drying method. Because of the strong interaction between TA and PVA through hydrogen bonds, PVA/TA/NaOH aerogels exhibited compressive moduli as high as 12.7 MPa, 20 times that of the control PVA aerogel. The microstructure of the aerogels in this study showed that the addition of NaOH disrupted the typical “card of house” aerogel structure, while the samples with TA showed a stereoscopic uniform structure. The thermal stabilities of aerogels were tested by thermogravimetric analysis, showing both a decrease on the onset of decomposition temperature, and a reduction in decomposition rate after initial char formation. The peak heat release rate and total heat release, as measured by cone calorimetry, dropped by 69% and 54%, respectively, after adding TA and NaOH

Effects of Fiber Reinforcement on Clay Aerogel Composites

Novel, low density structures which combine biologically-based fibers with clay aerogels are produced in an environmentally benign manner using water as solvent, and no additional processing chemicals. Three different reinforcing fibers, silk, soy silk, and hemp, are evaluated in combination with poly(vinyl alcohol) matrix polymer combined with montmorillonite clay. The mechanical properties of the aerogels are demonstrated to increase with reinforcing fiber length, in each case limited by a critical fiber length, beyond which mechanical properties decline due to maldistribution of filler, and disruption of the aerogel structure. Rather than the classical model for reinforced composite properties, the chemical compatibility of reinforcing fibers with the polymer/clay matrix dominated mechanical performance, along with the tendencies of the fibers to kink under compression

[Poly(ethylene terephthalate) Ionomer]/Silicate Hybrid Materials via Polymer-in situ Sol-Gel Reactions

A scheme was developed for producing poly(ethylene terephthalate (PET) ionomer)/silicate hybrid materials via polymer-in situ sol-gel reactions for tetraethylorthosilicate (TEOS) using different solvents. Scanning electron microscopy/EDAX studies revealed that silicate structures existed deep within PET ionomer films that were melt pressed from silicate-incorporated resin pellets. Si-29 solid-state NMR spectroscopy revealed considerable Si-O-Si bond formation, but also a significant fraction of SiOH groups. Na-23 solid-state NMR spectra suggested the presence of ionic aggregates within the unfilled PET ionomer, and that these aggregates do not suffer major structural rearrangements by silicate incorporation. For an ionomer treated with TEOS using MeCl2, Na+ ions are less associated with each other than in the unfilled control, suggesting silicate intrusion between PET-SO3- Na+ ion pair associations. The ionomer treated with TEOS + tetrachloroethane had more poorly formed ionic aggregates, which illustrates the influence of solvent type on ionic aggregation. First-scan DSC thermograms for the ionomers demonstrate an increase in crystallinity after the incorporation of silicates, but solvent-induced crystallization also appears to be operative. Second-scan DSC thermograms also suggest that the addition of silicate particles is not the only factor implicated in recrystallization, and that solvent type is important even in second-scan behavior. Silicate incorporation does not profoundly affect the second scan T-g vs. solvent type, i.e., chain mobility in the amorphous regions is not severely restricted by silicate incorporation. Recrystallization and melting in these hybrids appears to be due to an interplay between a solvent-induced crystallization that strongly depends on solvent type and interactions between PET chains and in situ grown, sol-gel-derived silicate particles. (C) 2002 Wiley Periodicals, Inc