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  • Open access
  • 75 Reads
Design of Cellulose Interfaces Through Self-Assembly of Adhesive Peptides with Intrinsic Stress-Sensitive Properties

The design of interfaces in green polymer composites is a crucial factor in ensuring mechanical strength in composite materials. While cellulose fibers have high intrinsic mechanical strength, their reinforcing effect in polymer composite materials highly relies on the creation of a tight interface with the surrounding polymer matrix. In parallel, the hydrophilicity of the cellulose has to be compatibilized with often more hydrophobic polymer matrixes. In this study, the cellulose interface has been modified by the self-assembly of polymer-peptide nanoparticles regulating the adhesive strength in the interface. The incorporation of catecholic groups allows physical adsorption at the cellulose surface in parallel with the mimicking of mussel-inspired adhesion in presence of dopamine groups. In this study, the cellulose surface modification has been performed with different concentrations of the adhesive nanoparticles, observing interesting trends in adhesive forces at either the nano- or macroscale length. The nanoscale adhesion has been tested with atomic force microscopy, showing the influence of nanoparticle deposits either as a monolayer or multilayer onto the cellulose surface. The macroscale adhesion was characterized by single-fiber pull out tests indicating an optimum concentration of nanoparticles at the surface to provide high adhesive interface strength. In addition, the nanoparticles show colorimetric and fluorescent response to mechanical shear stresses providing an evaluation tool to explore the interface phenomena upon failure.

  • Open access
  • 73 Reads
Wood Flour Treated with Pickering Emulsion Could Improve Its Composites with High-Density Polyethylene?

Silica synergistically stabilized paraffin Pickering emulsion is applied to modify wood flour (WF) for preparing wood/polymer composites. The effect of Pickering emulsion on properties of the WF and its composites with high-density polyethylene (HDPE) is investigated. The impregnation of paraffin Pickering emulsion could significantly improve the WF dispersion in HDPE matrix, resulting in increased melt flow index (MFI). It increased from 1.3 g/10 min (control) to 2.1 g/10 min (Pickering treatment) due to the lubrication of paraffin and rolling friction provided by silica nanoparticles. The hydrophobicity of the WF was improved by the penetration of paraffin and silica in the cell wall, which could consume the hydroxyl groups in WFs via hydrogen bonding. Owing to the well distribution of WFs and silica, the mechanical properties and surface hardness of the composites were enhanced obviously. The optimal tensile strength and impact strength increased 23% (18.28 MPa) and 32% (14.16 kJ/m2), respectively. It also could be attributed to the improved interfacial compatibility due to the incorporation of surfactants (Span 80 and Tween 80), which acted as a coupling agent. Furthermore, the silica incorporated in the WF could compensate the negative effect of paraffin on thermal stability of the composites. A model concerning the interactions in the composites was proposed based on the research results.

  • Open access
  • 103 Reads
Study of Defects and Geometric Anomalies on Monolayer Parts Obtained by Fused Deposition Modeling Process

The Fused Deposition Modeling (FDM) process, commonly known as 3D printing, deals with the manufacturing of parts by the subsequent addition of layers of fused thermoplastic polymer. The parts obtained by this process can be used for domestic applications, rapid prototyping, or final applications. During the preparation of the printing model, in the process known as slicing, different process parameters must be defined, such as: extruder speed, extruder height in relation to the bed, bed temperature. Parameters that, if incorrectly defined, can lead to a series of deficiencies in the parts, such as low dimensional accuracy, low surface quality, reduced mechanical resistance and, eventually, the occurrence of several printing defects in the parts,
damaging or even preventing its use. The 3D printing process has a critical period, at its beginning, during the manufacturing of the piece’s first layer. The present work aims to study some of the types of geometric deformations observed in monolayer pieces when some of the printing parameters are improperly defined. Printing tests on monolayer parts were carried out with polylactic acid (PLA) polymer filament. A home grade 3D printer, model Graber i3 was used. The height of the extruder to the bed was altered in relation to the recommended value, and three pieces were printed for each height used. The printed parts were scanned at 1200 x 1200 dpi resolution, using a DCP-L2540DW model scanner. The images obtained were then analyzed using the Matlab software and the geometric characteristics of the pieces were compared. The study is a first step towards a better understanding of the defects and geometric anomalies obtained when an incorrect definition of basic parameters during the processing of the three-dimensional model happens.

  • Open access
  • 161 Reads
Bisphenol-Free Epoxy Resins Derived from Natural Resources Exhibiting High Thermal Conductivity

Polymers and related polymer-based networks commonly have low thermal conductivity in the range of 0.1-0.2 W m-1 K-1, which is a limiting factor for their usage in the course of continuously increasing miniaturization and heat generation in electronic applications. Basically, two strategies can be applied in order to increase the transport of phonons in polymers: (i) the embedment of thermally conductive inorganic materials, yielding composite materials, and (ii) the involvement of aromatic units enabling microscopic anisotropy by pi-pi-stacking.

In this study, the thermal conductivity of resins based on Bisphenol A diglycidyl ether BADGE and 1,2,7,8-diepoxyoctane DEO was compared. DEO can be derived from pseudopelletierine, which is contained in the bark of the pomegranate tree. DEO-based epoxy resins, hence, potentially are a natural and sustainable alternative to BADGE. The epoxy compounds were cured with isophorone diamine IPDA and o-dianisidine DAN. Notably, isophorone diamine is derived from isophorone, which naturally occurs in cranberries. The formulations were produced without filler and with 5 wt.-% of SiO2 nanoparticles.

Significantly enhanced thermal conductivity in the range of 0.4 W m-1 K-1 occurs only in DEO-based polymer networks that were cured with DAN (and do not contain SiO2 fillers). This observation is argued to originate from pi-pi-stacking of the aromatic units of DAN enabled by the higher flexibility of the aliphatic carbon chain of DEO compared to that of BADGE. This assumption is further supported by the facts that significantly improved thermal conductivity occurs only above the glass-transition temperature (with higher flexibility of the polymer segments) and that nanoparticles appear to disrupt the pi-pi-stacking of the aromatic groups.In summary, it can be argued that the bisphenol-free epoxy/amine resin (with an epoxy compound derivable from natural resources) shows favorably higher thermal conductivity in comparison to the petrol-based bisphenol-based epoxy/amine resins.

  • Open access
  • 278 Reads
Dual/Bi-Stage Curing of Nanocomposites from Renewable Resources upon Volumetric Expansion

Nowadays, a large part of polymers for technical application are still obtained from petrochemicals, despite the more critical review by society. In this work, novel nanodielectrics based on renewable resources were developed. For this purpose, poly(2-oxazoline)s (POx), which can be referred to as pseudo-polyamides, were synthesized from renewable resources and compared with commercially available Nylon 12, which is derived from petrochemicals.

The monomers 2-nonyl-2-oxazozoline and 2-dec-9’-enyl-2-oxazoline were synthesized from coconut oil and castor oil in solvent-free syntheses according to the Henkel Patent; the copoly(2-oxazoline) was synthesized in energy-efficient fashion in microwave reactors under autoclave conditions.

Both types of polyamides (2 variations) were filled with inorganic nanoparticles (4 variations: no filler, submicro-scaled BN, nano- and micro-scaled AlN) and/or expanding monomers, namely spiro-orthoesters (3 variations: 0, 15, and 30 wt.-%), yielding a 2 x 4 x 3 = 24-membered material library. All polymers were crosslinked according to a newly developed thermally-initiated dual/bi-stage curing system.

Fundamental physico-chemical and dielectric characterization revealed that the relative volume expansion was in the range of 0.46-2.48 vol.-% for the Nylon 12 samples and in the range of 1.39-7.69 vol.-% for the POx samples. Hence, the formation micro-cracks or micro-voids during curing is significantly reduced. The dielectric measurements show competitive dielectric behaviour of the ‘green’ POx samples in comparison with the fossil-based Nylon 12 samples at a frequency of 40 Hz, rendering the pseudo-polyamides from natural resources as competitive dielectric.

  • Open access
  • 67 Reads
Self-assembly and Electrorheological Effect of Phthalocyanine-Based Liquid Crystalline Polysiloxanes

A series of phthalocyanine-based liquid crystalline polysiloxanes (PLCPs) were synthesized by use of poly(methylhydrogeno)siloxane (polymer matrix), a sulfonic acid-containg monomer 4-(allyloxy)benzenesulfonic acid, a liquid crystal monomer cholesteryl 4-(allyloxy)benzoate and a phthalocyanine-containing monomer zinc tetraaminophthalocyanine. The chemical structure, liquid crystal, dielectric and electrorheological properties were characterized via various experimental techniques. With increase of phthalocyanine in the supermolecular systems, the mesophases of PLCPs change from chiral nematic phase to discotic hexagonal columnar mesophase. Furthermore, the dielectric constant increases with increase of phthalocyanine component in the polymer systems. All the PLCPs exhibit electrorheological (ER) effect. For the ER fluid of PLCPs prepared by the same method, the ER effect strengthens firstly and then weakens with increase of phthalocyanine component in the polymers. The ER effect is strongest when the molar ratio of phthalocyanine and cholesteryl mesogens in the polymer is 8:2. This suggests some synergistic effect is occurred between semiconducting property and molecular orientation in these phthalocyanine-based liquid crystalline polysiloxanes.

  • Open access
  • 131 Reads
Applications and Properties by Using Time-resolved Fluorescence and Transient Absorption Spectroscopy

In this presentation, the absorption (transient absorption) and emission (steady state and time-resolved fluorescence) spectroscopy will be used to study, investigate and characterize the mechanisms of fluorescence quenching and obtaining new sensors for to detect toxic environments: heavy metals from water. For this purpose, new compounds were synthesized for to have a good fluorescence (high quantum yield), stability and selective sensibility. The study of fluorescence quenching by different metal ions such: Ni2+ , Cu2+ , Co2+ , Zn2+ , Fe3+ , Mn2+ , Ca2+ , Pb2+ , Cr3+ , Cd2+ , Sr2+ , Mg2+ will be study in solution, film at different temperature and variation in time for to demonstrate that these samples have a good stability and can be used as fluorescence sensors for the selective detection of metal ions. For fundamental study, theory of dynamic quenching, theory of static quenching and combined dynamic and static quenching were used, and the constants of the process, the lifetime in excited state, the quantum yield, the non-radiative and radiative rate constants were estimated. The lifetime, around 0.0001 s for each metal complexes was calculated by the analysis of the decays with and without oxygen. The emission from singlet oxygen was observed at 1275 nm in all samples, and the lifetime and quantum yield are dependent on the substitution on metal ions. Also, new application of the compounds investigated for detection of toxic environments (heavy metals- Fe) was obtain, sensor for to detect Fe from water.

  • Open access
  • 47 Reads
Polymer Nanocomposites for Lowering Heating and Cooling Loads in Buildings

Worldwide, buildings consume over 40% of the total commercial energy, and 36% of this amount is dedicated to heating and cooling of buildings. Therefore, building environment control systems require efficient thermal management (Ürge-Vorsatz et al., 2015). An ideal thermal management that could lower the energy load for cooling and heating respectively would combine passive strategies for thermal control, which are characterized by low cost, straightforward implementation, and energy efficiency, with the on-demand control of heating and cooling, specific for active thermal management strategies. This research was inspired by the capability of cephalopod skin to change the color in a dynamic manner, and such mechanism was applied for infrared radiation.

The scientific challenge of building an efficient platform for thermal control was addressed by using block copolymer materials in the development of nanocomposites with dynamically tunable thermal infrared properties. This has resulted in polymer-based materials capable of controlling a heat flux of 40 W/m2 with transient mechanical input of <3 W/m2 and capabilities for reflecting infrared radiation in a static manner as good as the reference material of the space blanket developed by NASA in 1960.

In indoor spaces, more than 50% of total heat exchange between the human body and the environment takes place through infrared radiation, with a maximum of human skin infrared emission around the wavelength of 9 microns. The prepared polymer-based materials modulate transmission and reflection of infrared radiation in a wide range of frequencies from near infrared to far infrared (up to 25 microns wavelength), thus being capable to modulate the heat exchange of the human body through radiation and the materials can be scaled to large surfaces on the order of square meters. Thus, the polymer nanocomposites manage 60-70 % of the metabolic heat flux from sedentary individuals and can modulate changes in the individual body temperature within a setpoint temperature range of 8 °C. This increase in the setpoint temperature translates into use of air conditioning for cooling/heating with a significantly lowered load, which would further translate into a 3 % decrease of global energy consumption.

  • Open access
  • 126 Reads
Value-added Wood Composites Made from Waste Polystyrene as a Binder: a Review

Wood composites is a growing field of products that are increasingly present for a variety of applications, with an undiminished upward trend now for very many decades. It must be clearly pointed out that one cannot speak about wood composites without speaking in depth of the polymer binders used to hold them together. Synthetic adhesives do still dominate this market and are mostly based on formaldehyde. There are also several biobased adhesives based on renewable natural materials that are at the forefront of new developments. Some of these are already industrial, sometime for many years, such as tannin adhesives and some soy adhesives, while others are on the way of industrialization, and many others are, as yet, at the experimental stage. Nowadays, the products manufactured from recycled materials are especially paid attention in the view-point of environmental problems. Polystyrene is a synthetic, aromatic, thermoplastic polymer made from the monomer styrene. Waste polystyrene poses serious environmental risks especially in developing countries where disposal facilities are lacking and its management is a serious problem because it is easy to recycle. Due to the lack of effective strategies of polystyrene waste recycling, most of it is discarded in recycling plants, landfills or incinerated. In this context, an option to successfully utilize waste polystyrene and at the same time to avoid the environmental problems that formaldehyde adhesives cause, is its application as a binder in order to produce value-added wood composites. This paper reviews the research milestones in this area and discusses the potential of using waste polystyrene as a binder in producing value-added wood composites.

  • Open access
  • 109 Reads
Polyelectrolyte Multilayer Thin Films Assembled Using Poly(N,N-dimethylaminoethyl methacrylate) and Polysaccharides: Versatile Platforms towards Protein Immobilization, Sorption of Organic Pollutants and Synthesis of Silver Nanoparticles

The interaction of materials with their surroundings proceeds mainly through their outer functional groups. Coating of solid materials with thin organic films using the Layer-by-Layer (LbL) assembly strategy is one of the most versatile approaches to fabricate functional surfaces for a wide range of applications. In this contribution, the functionalization of silica microparticles with LbL films containing poly(N,N-dimethylaminoethyl methacrylate) and polysaccharides (sodium alginate, carboxymethyl cellulose and chitosan) is investigated. All polymers used in this work are biocompatible, while the deposition strategy is environmentally benign and allows a precise control of the outer layer properties (chemical nature, charge, roughness, etc.). The application of the obtained films in immobilization of proteins/enzymes (i.e. pepsin, bovine serum albumin, hemoglobin and lysozyme), sorption/release of organic dyes (i.e. methylene blue, methyl orange, bromocresol green and Congo red), as well as their use as “green” catalysts for the synthesis of silver nanoparticles was investigated as a function of films’ composition, number of deposited layers and/or assembly conditions.