Functionalised polymer nanocomposites and blends

Functionalised polymer composites and blends were prepared with the aim of enhancing the mechanical and thermal properties of the polymer matrix, while maintaining the characteristic property (functionality) of the introduced functional group. This involved the use of nanoparticles with novel architecture (core cross-linked star polymers, POSS-functionalised dendrimers, telechelic POSS) to provide attributes for improving mechanical and thermal stability, in addition to physical aging stability and phase selectivity. Furthermore, nanoparticles were functionalised to provide attributes such as colour (dye-functionalised POSS) and magnetism (magnetite-functionalised carbon nanotubes). These nanoparticles were investigated in amorphous polymer matrices, with structure-property relationships explored. Core cross-linked star (CCS) increased the glass transition temperature (Tg) and decreased shrinkage of linear polystyrene and poly(methyl methacrylate). This was attributed to reduced volume within the blends and CCS polymer ‘arms’ imparting restrictions on segmental motions of polymer chains. These restrictions also enhanced thermomechanical properties and retarded structural relaxation. Volume relaxation was successfully observed in real time, creating a novel application for modulated temperature – thermomechanometry. POSS-functionalised dendrimers and telechelic POSS enhanced the thermal and mechanical properties of their respective elastomer matrices. Phase preference was successfully achieved via compatibilising ‘R’ groups on the POSS. Colour intensity was able to be controlled by altering the dye-functionalised POSS concentration. Material properties were influenced by filler concentration, phase preference and POSS architecture. Films became more magnetic with increasing carbon nanotube/magnetite concentration and films displayed superior mechanical and thermal properties. Melt-mixing was more effective at de-agglomerating and distributing functionalised CNTs than solvent dispersion. As a result, melt-mixed composites exhibited more dramatic changes in material properties and displayed superior magnetic, mechanical and thermal properties than their solvent dispersed counterparts

Habitat-Specific Morphological Variation among Threespine Sticklebacks (Gasterosteus aculeatus) within a Drainage Basin

Habitat-specific morphological variation, often corresponding to resource specialization, is well documented in freshwater fishes. In this study we used landmark based morphometric analyses to investigate morphological variation among threespine sticklebacks (Gasterosteus aculeatus L.) from four interconnected habitat types within a single lowland drainage basin in eastern England. These included the upper and lower reaches of the river, the estuary, a connected ditch network and a coastal salt marsh. We found significant habitat-specific differences in morphology, with three axes of variation describing differences in orbit diameter, body depth, caudal peduncle shape and pectoral fin positioning as well as variation in relative dorsal and pelvic spine size. Interestingly, the ditch system, an artificial and heavily managed habitat, is populated by sticklebacks with a characteristic morphology, suggesting that human management of habitats can in some circumstances lead to morphological variation among the animals that inhabit them. We discuss the mechanisms that conceivably underlie the observed morphological variation and the further work necessary to identify them. Finally, we consider the implications of habitat-specific body shape variation for the behavioural ecology of this ecologically generalist species

Polystyrene cellulose fiber composites: effect of the processing conditions on mechanical and dynamic mechanical properties

ABSTRACT The usage of natural fibers on the composites development has grown rapidly in the recent years due to the fibers plentiful availability, renewable source, low density and biodegradability. However, there are some drawbacks, for instance, the fiber dispersion on a polyolefin matrix. In this work, the influence of processing speed on the mechanical and dynamic mechanical properties of polystyrene (PS) filled with cellulose fiber composites was investigated. The composites were processed on a twin-screw co-rotating extruder, using screw speeds of 200 rpm, 400 rpm and 600 rpm. The dynamic mechanical properties and the mechanical properties were investigated as a function of fiber content. The composites processed on a screw speed of 400 rpm had presented an increase on flexural and impact strength, compared to the composites processed at 200 rpm. The flexural and storage modulus had increased when increasing the fiber content, as well as increasing the processing speed. The greater fiber dispersion obtained at a screw speed of 400 rpm hinders the agglomeration arrangement and distributes the fibers more equally on the matrix. The increase on processing speed probably generates a fiber size reduction, increasing the fiber superficial area and generating a greater contact with the matrix as well. Therefore, the efforts transference of matrix to fibers is improved, originating an increase on the evaluated properties

Materials produced from plant biomass: part II: evaluation of crystallinity and degradation kinetics of cellulose

In this study Eucalyptus grandis (CEG) and Pinus taeda (CPT) cellulose fibers obtained from kraft and sulfite pulping process, respectively, were characterized using Fourier transform infrared (FTIR) spectroscopy and thermogravimetry (TGA). The degradation kinetic parameters were determined by TGA using Coats and Redfern method. FTIR results showed that CPT presented a more ordered structure with higher crystallinity than CEG. Thermogravimetric results showed that CPT had a higher thermal stability than CEG. The kinetic results revel that for CEG the degradation mechanism occurs mainly by random nucleation, although phase boundary controlled reactions also occurs while for CPT the degradation process is more related with phase boundary controlled reactions. Results demonstrated that differences between thermal stability and degradation mechanisms might be associated with differences in the cellulose crystalline structure probably caused by different pulping processes used for obtaining the cellulose fibers

Static and modulated-force mechanical properties of functionalised POSS-elastomer nanocomposites

Dumbbell-shaped dimeric polyhedral oligomeric silsesquioxanes (POSS) molecules were synthesised and incorporated into poly(styrene-b-butadiene-b-styrene) (SBS) as nano-fillers via physical blending to prepare novel thermoplastic elastomer nanocomposites. The POSS molecules contained either isobutyl or phenyl compatibilising groups to provide selectivity with either the soft (butadiene) or hard (phenyl) phases within SBS, respectively. Tensile mechanical, dynamic mechanical and creep-recovery properties were determined. Creep was modeled using the 4-element model of Maxwell and Kelvin-Voigt, while recovery correlated with the stretched-exponential function of Kohlrausch, Williams and Watts

Poly(styrene-b-butadiene-b-styrene) - dye-coupled polyhedral oligomeric silsesquioxanes

Dye-coupled polyhedral oligomeric silsesquioxane (POSS) were prepared and the coloured POSS particles were ultrasonically solution dispersed in poly(styrene-b-butadiene-bstyrene) (SBS). POSS molecules contained either isobutyl or phenyl groups to provide selective compatibility with either the soft (butadiene) or hard (styrene) phase within the block copolymer. The composition and thermal stability were characterised using thermogravimetry. Colour coordinates were measured. Tensile mechanical properties, creep and recovery were determined. Creep was modeled using the 4-element model of Maxwell and Kelvin-Voigt, while recovery correlated with the stretched-exponential function of Kohlrausch, Williams and Watts

Novel elastomer dye-functionalised POSS nanocomposites: Enhanced colourimetric, thermomechanical and thermal properties

Nanocomposites consisting of poly(styrene-b-butadiene-b-styrene) (SBS) and polyhedral oligomeric silsesquioxanes (POSS) were prepared using a solvent dispersion method. POSS molecules were functionalised with two dichlorotriazinereactive dyes (CI Reactive Blue 4, CI Reactive Red 2) prior to compounding. Infrared spectroscopy confirmed functionalisation. Scanning electron microscopy revealed an increase in filler aggregation with concentration, with preferential phase selectivity. Ultraviolet spectroscopy and colourimetry confirmed colour uniformity and suggested that colour intensity could be controlled. Functionalised POSS improved thermal stability by imparting restrictions on SBS chain motions. Tensile stress-strain analysis revealed an increase in modulus with filler concentration, while creep deformation decreased and permanent strain increased with POSS content. Storage modulus, loss modulus and glass transition temperature increased with filler content due to effective SBS-POSS interaction. Nanocomposite properties were influenced by the phase the filler was dispersed throughout and the structure of the dye chromophore

One-pot, mouldable, thermoplastic resins from poly(propylene carbonate) and poly(caprolactone triol)

Co-polymers of poly(propylene carbonate) (PPC) and poly(caprolactone triol) (PCLT) were synthesised via a simple yet effective one-pot, two-step method, without the need for a catalyst or solvent. Successful synthesis was confirmed via H-1 NMR and ATR-FT-IR. The co-polymers displayed increased thermal stability. Covalent bonding between the functionalised PCLT and PPC enhanced moduli and strength, while also reducing creep and flow within PPC. Co-polymers displayed increased storage moduli, glass transition temperatures and damping properties. Additionally, PCLT-PPC co-polymers were flexible and easily moulded into shapes while maintaining their form and structural integrity. By imparting a relatively small concentration of functionalised-PCLT, the existing material properties (damping), as well as those previously seen as a hindrance to greater PPC application (poor thermal stability, cold flow, poor strength) were enhanced, while new characteristics (mouldability) were introduced.Peer reviewe

POSS-substituted hyperbranched polyester blends with thermoplastic polyurethanes

The aim of this research is to prepare and disperse in an elastomer a multi-branched form of POSS. Hyperbranched polymers (HBP) can be formed by grafting from a central core. POSS may be joined with a bifunctional reactant to form a bi-POSS joined by a single chain consisting of adipate (6C) or sebacate (10C). A hyperbranched polyester has been used as a core for attachment of multiple POSS molecules to create a large arrange of pendant POSS. The multi-POSS hyperbranched polyester core is a single molecule with polydispersity of branches and POSS attachments, so its mixtures with a polymer, in this case a thermoplastic polyurethane are technically blends, even though the POSS derivative may have the shape of a filler. Creep was retarded by the presence of multi-POSS. Recovery occurred with low permanent deformation, though the rate of recovery was decreased by the multi-POSS, which caused a greater skewness of the recovery curve deviating from exponential decay consistent with an increased distribution of relaxation times. The storage modulus increased with increase in the concentration of multi-POSS in the blends, while the damping factor was reduced

Novel polyhedral oligomeric silsesquioxane-substituted dendritic polyester tougheners for linear thermoplastic polyurethane

Boltorn hyperbranched aliphatic polyesters were functionalized with polyhedral oligomeric silsesquioxane (POSS) and incorporated into linear thermoplastic polyurethane (TPU). Increasing POSS-functionalized Boltorn concentration led to an increase in agglomerate size and frequency, due to interactions between POSS molecules. The Boltorn dendrimer primarily influenced the morphology of the blends. Blends displayed enhanced thermal stability, due to restrictions on chain segmental motions imparted by the Boltorn and thermal shielding by POSS. Increasing the blend concentration resulted in higher tensile modulus and strength, while ductility decreased due to increased rigidity. Creep deformation decreased and permanent deformation increased with increased Boltorn content, while E', E?, and T g values all increased. TPU blended with higher generation functionalized-Boltorn displayed superior thermal and mechanical properties than those containing lower generation dendrimer, due to enhanced interaction and restrictions on TPU chain segments. Both the Boltorn and POSS contributed to material properties