Reactive processing of polymers:functionalisation of ethylene-propylene diene terpolymer (EPDM) in the presence and absence of a co-agent and effect of functionalised EPDM on compatibilisation of poly(ethylene terephthalate)/EPDM blends

Ethylene-propylene diene terpolymer (EPDM) was functionalized with glycidyl methacrylate (GMA) during melt processing by free radical grafting with peroxide initiation in the presence and absence of a reactive comonomer trimethylolpropane triacrylate (Tris). Increasing the peroxide concentration resulted in an increase in the GMA grafting yield, albeit the overall grafting level was low and was accompanied by higher degree of crosslinking of EPDM which was found to be the major competing reaction. The presence of Tris in the grafting system gave rise to higher grafting yield produced at a much lower peroxide concentration though the crosslinking reactions remained high but without the formation of GMA-homopolymer in either of the two systems. The use of these functionalized EPDM (f-EPDM) samples with PET as compatibilisers in binary and ternary blends of PET/EPDM/f-EPDM was evaluated. The influence of the different functionalisation routes of the rubber phase (in presence and absence of Tris) and the effect of the level of functionality and microstructure of the resultant f-EPDM on the extent of the interfacial reaction, morphology and mechanical properties was also investigated. It is suggested that the mechanical properties of the blends are strongly influenced by the performance of the graft copolymer, which is in turn, determined by the level of functionality, molecular structure of the functionalized rubber and the interfacial concentration of the graft copolymer across the interface. The cumulative evidence obtained from torque rheometry, scanning electron microscopy, SEM, dynamic mechanical analysis (DMA), tensile mechanical tests and Fourier transform infrared (FTIR) supports this. It was shown that binary and ternary blends prepared with f-EPDM in the absence of Tris and containing lower levels of g-GMA effected a significant improvement in mechanical properties. This increase, particularly in elongation to break, could be accounted for by the occurrence of a reaction between the epoxy groups of GMA and the hydroxyl/carboxyl end groups of PET that would result in a graft copolymer which could, most probably, preferentially locate at the interface, thereby acting as an 'emulsifier' responsible for decreasing the interfacial tension between the otherwise two immiscible phases. This is supported by results from FTIR analysis of the fractionated PET phase of these blends which confirm the formation of an interfacial reaction, DMA results which show a clear shift in the T s of the blend components and SEM results which reveal very fine morphology, suggesting effective compatibilisation that is concomitant with the improvement observed in their tensile properties. Although Tris has given rise to highest amount of g-GMA, it resulted in lower mechanical properties than the optimized blends produced in the absence of Tris. This was attributed to the difference in the microstructure of the graft and the level of functionality in these samples resulting in less favourable structure responsible for the coarser dispersion of the rubber phase observed by SEM, the lower extent of T shift of the PET phase (DMA), the lower height of the torque curve during reactive blending and FTIR analysis of the separated PET phase that has indicated a lower extent of the interfacial chemical reaction between the phases in this Tris-containing blend sample. © 2005 Elsevier Ltd. All rights reserved.

Reactive processing of polymers:effect of in situ compatibilisation on characteristics of blends of polyethylene terephthalate and ethylene-propylene rubber

Ethylene-propylene rubber (EPR) functionalised with glycidyl methacrylate (GMA) (f-EPR) during melt processing in the presence of a co-monomer, such as trimethylolpropane triacrylate (Tris), was used to promote compatibilisation in blends of polyethylene terephthalate (PET) and f-EPR, and their characteristics were compared with those of PET/f-EPR reactive blends in which the f-EPR was functionalised with GMA via a conventional free radical melt reaction (in the absence of a co-monomer). Binary blends of PETand f-EPR (with two types of f-EPR prepared either in presence or absence of the co-monomer) with various compositions (80/20, 60/40 and 50/50 w/w%) were prepared in an internal mixer. The blends were evaluated by their rheology (from changes in torque during melt processing and blending reflecting melt viscosity, and their melt flow rate), morphology scanning electron microscopy (SEM), dynamic mechanical properties (DMA), Fourier transform infrared (FTIR) analysis, and solubility (Molau) test. The reactive blends (PET/f-EPR) showed a marked increase in their melt viscosities in comparison with the corresponding physical (PET/EPR) blends (higher torque during melt blending), the extent of which depended on the amount of homopolymerised GMA (poly-GMA) present and the level of GMA grafting in the f-EPR. This increase was accounted for by, most probably, the occurrence of a reaction between the epoxy groups of GMA and the hydroxyl/carboxyl end groups of PET. Morphological examination by SEM showed a large improvement of phase dispersion, indicating reduced interfacial tension and compatibilisation, in both reactive blends, but with the Tris-GMA-based blends showing an even finer morphology (these blends are characterised by absence of poly-GMA and presence of higher level of grafted GMA in its f-EPR component by comparison to the conventional GMA-based blends). Examination of the DMA for the reactive blends at different compositions showed that in both cases there was a smaller separation between the glass transition temperatures compared to their position in the corresponding physical blends, which pointed to some interaction or chemical reaction between f-EPR and PET. The DMA results also showed that the shifts in the Tgs of the Tris-GMA-based blends were slightly higher than for the conventional GMA-blends. However, the overall tendency of the Tgs to approach each other in each case was found not to be significantly different (e.g. in a 60/40 ratio the former blend shifted by up to 4.5 °C in each direction whereas in the latter blend the shifts were about 3 °C). These results would suggest that in these blends the SEM and DMA analyses are probing uncorrelatable morphological details. The evidence for the formation of in situ graft copolymer between the f-EPR and PET during reactive blending was clearly illustrated from analysis by FTIR of the separated phases from the Tris-GMA-based reactive blends, and the positive Molau test pointed out to graft copolymerisation in the interface. A mechanism for the formation of the interfacial reaction during the reactive blending process is proposed.

Reactive processing of polymers:melt grafting of glycidyl methacrylate on ethylene propylene copolymer in the presence of a coagent

Glycidyl methacrylate (GMA) was grafted on ethylene-propylene copolymer during melt processing with peroxide initiation in the presence and absence of a more reactive comonomer (coagent), trimethylolpropane triacrylate (Tris). The characteristics of the grafting systems in terms of the grafting reaction yield and the nature and extent of the competing side reactions were examined. The homopolymers of GMA (Poly-GMA) and Tris (Poly-Tris) and the GMA-Tris copolymer (GMA-co-Tris) were synthesized and characterized. In the absence of the coagent, high levels of poly-GMA, which constituted the major competing reaction, was formed, giving rise to low GMA grafting levels. Further, this grafting system resulted in a high extent of gel formation and polymer crosslinking due to the high levels of peroxide needed to achieve optimum GMA grafting and a consequent large drop in the melt index (increased viscosity) of the polymer. In the presence of the coagent, however, the grafting system required much lower peroxide concentration, by almost an order of magnitude, to achieve the optimum grafting yield. The coagent-containing GMA-grafting system has also resulted in a drastic reduction in the extent of all competing reactions, and in particular, the GMA homopolymerization, leading to improved GMA grafting efficiency with no detectable gel or crosslinking. The mechanisms of the grafting reactions, in the presence and absence of Tris, are proposed.

A Model of Lung Tumor Angiogenesis in a Biomimetic Poly(ethylene glycol)-based Hydrogel System

Tumor angiogenesis is critical to tumor growth and metastasis, yet much is unknown about the role vascular cells play in the tumor microenvironment. A major outstanding challenge associated with studying tumor angiogenesis is that existing preclinical models are limited in their recapitulation of in vivo cellular organization in 3D. This disparity highlights the need for better approaches to study the dynamic interplay of relevant cells and signaling molecules as they are organized in the tumor microenvironment. In this thesis, we combined 3D culture of lung adenocarcinoma cells with adjacent 3D microvascular cell culture in 2-layer cell-adhesive, proteolytically-degradable poly(ethylene glycol) (PEG)-based hydrogels to study tumor angiogenesis and the impacts of neovascularization on tumor cell behavior.

In initial studies, 344SQ cells, a highly metastatic, murine lung adenocarcinoma cell line, were characterized alone in 3D in PEG hydrogels. 344SQ cells formed spheroids in 3D culture and secreted proangiogenic growth factors into the conditioned media that significantly increased with exposure to transforming growth factor beta 1 (TGF-β1), a potent tumor progression-promoting factor. Vascular cells alone in hydrogels formed tubule networks with localized activated TGF-β1. To study cancer cell-vascular cell interactions, the engineered 2-layer tumor angiogenesis model with 344SQ and vascular cell layers was employed. Large, invasive 344SQ clusters developed at the interface between the layers, and were not evident further from the interface or in control hydrogels without vascular cells. A modified model with spatially restricted 344SQ and vascular cell layers confirmed that observed 344SQ cluster morphological changes required close proximity to vascular cells. Additionally, TGF-β1 inhibition blocked endothelial cell-driven 344SQ migration.

Two other lung adenocarcinoma cell lines were also explored in the tumor angiogenesis model: primary tumor-derived metastasis-incompetent, murine 393P cells and primary tumor-derived metastasis-capable human A549 cells. These lung cancer cells also formed spheroids in 3D culture and secreted proangiogenic growth factors into the conditioned media. Epithelial morphogenesis varied for the primary tumor-derived cell lines compared to 344SQ cells, with far less epithelial organization present in A549 spheroids. Additionally, 344SQ cells secreted the highest concentration of two of the three angiogenic growth factors assessed. This finding correlated to 344SQ exhibiting the most pronounced morphological response in the tumor angiogenesis model compared to the 393P and A549 cell lines.

Overall, this dissertation demonstrates the development of a novel 3D tumor angiogenesis model that was used to study vascular cell-cancer cell interactions in lung adenocarcinoma cell lines with varying metastatic capacities. Findings in this thesis have helped to elucidate the role of vascular cells in tumor progression and have identified differences in cancer cell behavior in vitro that correlate to metastatic capacity, thus highlighting the usefulness of this model platform for future discovery of novel tumor angiogenesis and tumor progression-promoting targets.

Co-production of bio-oil and propylene through the hydrothermal liquefaction of polyhydroxybutyrate producing cyanobacteria

A polyhydroxybutyrate (PHB) producing cyanobacteria was converted through hydrothermal liquefaction (HTL) into propylene and a bio-oil suitable for advanced biofuel production. HTL of model compounds demonstrated that in contrast to proteins and carbohydrates, no synergistic effects were detected when converting PHB in the presence of algae. Subsequently, Synechocystis cf. salina, which had accumulated 7.5wt% PHB was converted via HTL (15% dry weight loading, 340°C). The reaction gave an overall propylene yield of 2.6%, higher than that obtained from the model compounds, in addition to a bio-oil with a low nitrogen content of 4.6%. No propylene was recovered from the alternative non-PHB producing cyanobacterial strains screened, suggesting that PHB is the source of propylene. PHB producing microorganisms could therefore be used as a feedstock for a biorefinery to produce polypropylene and advanced biofuels, with the level of propylene being proportional to the accumulated amount of PHB.

Co-production of bio-oil and propylene through the hydrothermal liquefaction of polyhydroxybutyrate producing cyanobacteria

A polyhydroxybutyrate (PHB) producing cyanobacteria was converted through hydrothermal liquefaction (HTL) into propylene and a bio-oil suitable for advanced biofuel production. HTL of model compounds demonstrated that in contrast to proteins and carbohydrates, no synergistic effects were detected when converting PHB in the presence of algae. Subsequently, Synechocystis cf. salina, which had accumulated 7.5wt% PHB was converted via HTL (15% dry weight loading, 340°C). The reaction gave an overall propylene yield of 2.6%, higher than that obtained from the model compounds, in addition to a bio-oil with a low nitrogen content of 4.6%. No propylene was recovered from the alternative non-PHB producing cyanobacterial strains screened, suggesting that PHB is the source of propylene. PHB producing microorganisms could therefore be used as a feedstock for a biorefinery to produce polypropylene and advanced biofuels, with the level of propylene being proportional to the accumulated amount of PHB.

Proteomic and phosphoproteomic analysis of polyethylene glycol-induced osmotic stress in root tips of common bean (Phaseolus vulgaris L.)

Previous studies have shown that polyethylene glycol (PEG)-induced osmotic stress (OS) reduces cell-wall (CW) porosity and limits aluminium (Al) uptake by root tips of common bean (Phaseolus vulgaris L.). A subsequent transcriptomic study suggested that genes related to CW processes are involved in adjustment to OS. In this study, a proteomic and phosphoproteomic approach was applied to identify OS-induced protein regulation to further improve our understanding of how OS affects Al accumulation. Analysis of total soluble proteins in root tips indicated that, in total, 22 proteins were differentially regulated by OS; these proteins were functionally categorized. Seventy-seven per- cent of the total expressed proteins were involved in metabolic pathways, particularly of carbohydrate and amino acid metabolism. An analysis of the apoplastic proteome revealed that OS reduced the level of five proteins and increased that of seven proteins. Investigation of the total soluble phosphoproteome suggested that dehydrin responded to OS with an enhanced phosphorylation state without a change in abundance. A cellular immunolocalization analysis indicated that dehydrin was localized mainly in the CW. This suggests that dehydrin may play a major protective role in the OS-induced physical breakdown of the CW structure and thus maintenance of the reversibility of CW extensibility during recovery from OS. The proteomic and phosphoproteomic analyses provided novel insights into the complex mechanisms of OS-induced reduction of Al accumulation in the root tips of common bean and highlight a key role for modification of CW structure.

I. Nickel-Exchanged Zincosilicate Catalysts for the Oligomerization of Propylene and II. Organic SDA-Free Catalysts for the Methanol-to-Olefins Reaction

Nickel-containing catalysts are developed to oligomerize light olefins. Two nickel-containing zincosilicates (Ni-CIT-6 and Ni-Zn-MCM-41) and two nickel-containing aluminosilicates (Ni-HiAl-BEA and Ni-USY) are synthesized as catalysts to oligomerize propylene into C_3n (C₆ and C₉) products. All catalysts oligomerize propylene, with the zincosilicates demonstrating higher average selectivities to C_3n products, likely due to the reduced acidity of the Zn heteroatom.

To test whether light alkanes can be incorporated into this oligomerization reaction, a supported homogeneous catalyst is combined with Ni-containing zincosilicates. The homogeneous catalyst is included to provide dehydrogenation/hydrogenation functions. When this tandem catalyst system is evaluated using a propylene/n-butane feed, no significant integration of alkanes are observed.

Ni-containing zincosilicates are reacted with 1-butene and an equimolar propylene/1-butene mixture to study other olefinic feeds. Further, other divalent metal cations such as Mn²⁺, Co²⁺, Cu²⁺, and Zn²⁺ are exchanged onto CIT-6 samples to investigate stability and potential use for other reactions. Co-CIT-6 oligomerizes propylene, albeit less effectively than Ni-CIT-6. The other M-CIT-6 samples, while not able to oligomerize light olefins, may be useful for other reactions, such as deNO_x.

Molecular sieves are synthesized, characterized, and used to catalyze the methanol-to-olefins (MTO) reaction. The Al concentration in SSZ-13 samples is varied to investigate the effect of Al number on MTO reactivity when compared to a SAPO-34 sample with only isolated Si Brønsted acid sites. These SSZ-13 samples display reduced transient selectivity behavior and extended reaction lifetimes as Si/Al increases; attributable to fewer paired Al sites. MTO reactivity for the higher Si/Al SSZ-13s resembles the SAPO-34 sample, suggesting that both catalysts owe their stable reaction behavior to isolated Brønsted acid sites.

Zeolites CHA and RHO are prepared without the use of organic structure-directing agents (OSDAs), dealuminated by steam treatments (500°C-800°C), and evaluated as catalysts for the MTO reaction. The effects of temperature and steam partial pressure during steaming are investigated. X-ray diffraction (XRD) and Ar physisorption show that steaming causes partial structural collapse of the zeolite, with degradation increasing with steaming temperature. ²⁷Al MAS NMR spectra of steamed materials reveal the presence of tetrahedral, pentacoordinate, and hexacoordinate aluminum.

Proton forms of as-synthesized CHA (Si/Al=2.4) and RHO (Si/Al=2.8) rapidly deactivate under MTO testing conditions (400°C, atmospheric pressure). CHA samples steamed at 600°C performed best among samples tested, showing increased olefin selectivities and catalyst lifetime. Acid washing these steamed samples further improved activity. Reaction results for RHO were similar to CHA, with the RHO sample steamed at 800°C producing the highest light olefin selectivities. Catalyst lifetime and C₂-C₃ olefin selectivities increase with increasing reaction temperature for both CHA-type and RHO-type steamed samples.

Differential effects of low-temperature inhibition on the propylene induced autocatalysis of ethylene production, respiration and ripening of 'Hayward' kiwifruit

Previous studies (Stavroulakis and Sfakiotakis, 1993) have shown an inhibition of propylene-induced ethylene production in kiwifruit below a critical temperature range of 11-14.8 degrees C. The aim of this research was to identify the biochemical basis of this inhibition in kiwifruit below 11-14.8 degrees C. 'Hayward' kiwifruit were treated with increasing propylene concentrations at 10 and 20 degrees C. Ethylene biosynthesis pathways and fruit ripening were investigated. Kiwifruit at 20 degrees C in air started autocatalysis of ethylene production and ripened after 19 d with a concomitant increase in respiration. Ethylene production and the respiration rise appeared earlier with increased propylene concentrations. Ripening proceeded immediately after propylene treatment, while ethylene autocatalysis needed a lag period of 24-72 h. The latter event was attributed to the delay found in the induction of 1-aminocyclopropane-1-carboxylate synthase (ACC synthase) activity and consequently to the delayed increase of l-aminocyclopropane l-carboxylic acid (ACC) content. In contrast propylene treatment induced 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase) activity with no lag period. Moreover, transcription of ACC synthase and ACC oxidase genes was active only in ethylene-producing kiwifruit at 20 degrees C. In contrast, treatment at 10 degrees C with propylene strongly inhibited ethylene production, which was attributed to the low activities of both ACC synthase and ACC oxidase as well as the low initial ACC level. Interestingly, fruit treated with propylene at 10 degrees C appeared to be able to transcribe the ACC oxidase but not the ACC synthase gene. However, propylene induced ripening of that fruit almost as rapidly as in the propylene-treated fruit at 20 degrees C. Respiration rate was increased together with propylene concentration. It is concluded that kiwifruit stored at 20 degrees C behaves as a typical climacteric fruit, while at 10 degrees C behaves like a non-climacteric fruit. We propose that the main reasons for the inhibition of the propylene induced (autocatalytic) ethylene production in kiwifruit at low temperature (less than or equal to 10 degrees C), are primarily the suppression of the propylene-induced ACC synthase gene expression and the possible post-transcriptional modification of ACC oxidase.

Flixweed vs. Polyethylene Glycol in the Treatment of Childhood Functional Constipation: A Randomized Clinical Trial

Background: Polyethylene glycol (PEG) is often considered as the first-line treatment for functional constipation in children. Descurainia sophia (L.) Webb et Berth (D. sophia) is a safe recommended medicine in Iranian folk and Traditional Persian Medicine for the treatment of constipation. Objectives: To clinically compare D. sophia with PEG 4000 (without electrolyte) in pediatric constipation and to assess its efficacy and side effects. Patients and Methods: 120 patients aged 2 - 12 years with constipation for at least 3 months were included in an 8 weeks lasting randomized controlled trial within two parallel-groups. Children received either PEG, 0.4 g/kg/day, or D. sophia seeds, 2 grams (for children aged 2 - 4 years) and 3 grams (for those aged > 4 years) per day. Results: A total of 109 patients completed the study (56 in D. sophia and 53 in PEG group). At the end of the study, 36 (64.3%) patients in D. sophia group and 29 (54.7%) in PEG group were out of Rome III criteria (P = 0.205). Median weekly stool frequency in 0, 1, 2, 3 weeks of the treatment was found to be 2, 5, 5, 5 in D. sophia and 3, 4, 4, 5 in PEG group (P = 0.139, 0.076, 0.844, 0.294), respectively. The number of patients who suffered flatulence was less (5, 8.9%) in D. sophia group as compared to PEG group (6, 11.3%) at the end of the trial (P = 0.461). D. sophia taste was less tolerated. Conclusions: D. sophia is introduced as a cheap and available medication which can be applied as a safe alternative to conventional PEG in the management of pediatric chronic functional constipation.

Differential effects of low-temperature inhibition on the propylene induced autocatalysis of ethylene production, respiration and ripening of 'Hayward' kiwifruit

Previous studies (Stavroulakis and Sfakiotakis, 1993) have shown an inhibition of propylene-induced ethylene production in kiwifruit below a critical temperature range of 11-14.8 degrees C. The aim of this research was to identify the biochemical basis of this inhibition in kiwifruit below 11-14.8 degrees C. 'Hayward' kiwifruit were treated with increasing propylene concentrations at 10 and 20 degrees C. Ethylene biosynthesis pathways and fruit ripening were investigated. Kiwifruit at 20 degrees C in air started autocatalysis of ethylene production and ripened after 19 d with a concomitant increase in respiration. Ethylene production and the respiration rise appeared earlier with increased propylene concentrations. Ripening proceeded immediately after propylene treatment, while ethylene autocatalysis needed a lag period of 24-72 h. The latter event was attributed to the delay found in the induction of 1-aminocyclopropane-1-carboxylate synthase (ACC synthase) activity and consequently to the delayed increase of l-aminocyclopropane l-carboxylic acid (ACC) content. In contrast propylene treatment induced 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase) activity with no lag period. Moreover, transcription of ACC synthase and ACC oxidase genes was active only in ethylene-producing kiwifruit at 20 degrees C. In contrast, treatment at 10 degrees C with propylene strongly inhibited ethylene production, which was attributed to the low activities of both ACC synthase and ACC oxidase as well as the low initial ACC level. Interestingly, fruit treated with propylene at 10 degrees C appeared to be able to transcribe the ACC oxidase but not the ACC synthase gene. However, propylene induced ripening of that fruit almost as rapidly as in the propylene-treated fruit at 20 degrees C. Respiration rate was increased together with propylene concentration. It is concluded that kiwifruit stored at 20 degrees C behaves as a typical climacteric fruit, while at 10 degrees C behaves like a non-climacteric fruit. We propose that the main reasons for the inhibition of the propylene induced (autocatalytic) ethylene production in kiwifruit at low temperature (less than or equal to 10 degrees C), are primarily the suppression of the propylene-induced ACC synthase gene expression and the possible post-transcriptional modification of ACC oxidase.

New biomaterials for packaging: a green approach to biopolymers and biocomposites

The impellent global environmental issues related to plastic materials can be addressed by following two different approaches: i) the development of synthetic strategies towards novel bio-based polymers, deriving from biomasses and thus identifiable as CO2-neutral materials, and ii) the development of new plastic materials, such as biocomposites, which are bio-based and biodegradable and therefore able to counteract the accumulation of plastic waste. In this framework, this dissertation presents extensive research efforts have been devoted to the synthesis and characterization of polyesters based on various bio-based monomers, including ω-pentadecalactone, vanillic acid, 2,5-furan dicarboxylic acid, and 5-hydroxymethylfurfural. With the aim of achieving high molecular weight polyesters, different synthetic strategies have been used as melt polycondensation, enzymatic polymerization, ring-opening polymerization and chain extension reaction. In particular, poly(ethylene vanillate) (PEV), poly(ω-pentadecalactone) (PPDL), poly(ethylene vanillate-co-pentadecalactone) (P(EV-co-PDL)), poly(2-hydroxymethyl 5-furancarboxylate) (PHMF), poly(ethylene 2,5-furandicarboxylate) (PEF) with different amount of diethylene glycol (DEG) unit amount, poly(propylene 2,5-furandicarboxylate) (PPF), poly(hexamethylene 2,5-furandicarboxylate), (PHF) have been prepared and extensively characterized. To improve the lacks of poly(hydroxybutyrate-co-valerate) (PHBV), its minimal formulations with natural additives and its blending with medium chain length PHAs (mcl-PHAs) have been tested. Additionally, this dissertation presents new biocomposites based on polylactic acid (PLA), poly(butylene succinate) (PBS), and PHBV, which are polymers both bio-based and biodegradable. To maintain their biodegradability only bio-fillers have been taken into account as reinforcing agents. Moreover, the commitment to sustainability has further limited the selection and led to the exclusive use of agricultural waste as fillers. Detailly, biocomposites have been obtained and discussed by using the following materials: PLA and agro-wastes like tree pruning, potato peels, and hay leftovers; PBS and exhausted non-compliant coffee green beans; PHBV and industrial starch extraction residues.