Eren Simsek

Dual scale roughness driven perfectly hydrophobic surfaces prepared by electrospraying a polymer in good solvent-poor solvent systems

We demonstrated a facile method to produce perfectly hydrophobic surfaces (advancing and receding angles both 180°) via electrospraying. When a copolymer of styrene and a perfluoroacrylate monomer was electrosprayed in good solvents, surfaces composed of micrometer size beads were formed and fairly low threshold water sliding angles could be achieved. Addition of high boiling point poor solvents to the solutions resulted nanoscale roughness on the beads due to a possible phase separation that occurs in a predominantly poor solvent environment. However, sliding angles were not zero even on the nanoscale roughness dominated topographies achieved by this method. On the other hand, when the electrospraying process parameters were set such that micrometer size hills of nanoscopically rough beads were formed, 0° sliding angles were measured. Videos of droplets recorded and the adhesive forces measured during a contact and release experiment revealed that these dual scale rough surfaces were indeed perfectly hydrophobic. Application of the method with other binary good solvent-poor solvent systems also resulted in perfect hydrophobicity. Overall results showed how the differences in surface topology affected the wettability of surfaces within a very narrow range between perfect and extreme hydrophobicity (advancing and receding angles both close to 180°).

Poly(propylene)/waste vulcanized ethylene- propylene-diene monomer (PP/WEPDM) blends prepared by high-shear thermo-kinetic mixer

Polypropylene (PP)–waste elastomer blends are particularly attractive as an economical way of producing sustainable materials, relieving the stress on the environment. Although PP is a commodity thermoplastic finding employment in various applications, its relatively low impact strength might be a significant factor limiting the variety of uses in many industries. Extensive consumption of thermoset elastomers has been a worldwide waste disposal problem. Here, we describe a facile, economical method for reuse of waste ethylene-propylene-diene monomer (EPDM) rubber to produce impact resistant blend materials with the PP via a high-shear thermokinetic mixer. In these blends, waste EPDM was used in various concentrations ranging from 20 to 80 wt%, as the remaining part, PP acts as a carrier matrix or a physical binder depending on the concentration in the blend. Briefly, fivefold increase was achieved in the impact resistance of PP by the addition of 60 wt% EPDM waste. The blend with 80 wt% waste EPDM shows characteristics similar to a thermoplastic elastomer. The conclusion of the study is that the blending method is quite effective to produce high-performance blend materials consisting of high concentrations of thermoset waste which addresses the worldwide disposal problem of waste thermoset rubbers.

Effect of soft segment molecular weight on the glass transition, crystallinity, molecular mobility and segmental dynamics of poly(ethylene oxide) based poly(urethane–urea) copolymers

The effect of poly(ethylene oxide) (PEO) soft segment molecular weight (Mn = 2000, 4600 and 8000 g mol−1) on the glass transition, crystallinity, molecular mobility and segmental dynamics of a series of aliphatic polyurethaneurea copolymers (PUU) with a constant hard segment content of 30% by weight was investigated using differential scanning calorimetry and dielectric relaxation spectroscopy. The soft segment (PEO) glass transition temperature increased with increasing molecular weight. Furthermore, five different relaxations were observed in dielectric analyses of all copolymers. These included local glassy state motions (γ) and (β), segmental motion of the soft phase (α), conductivity relaxation, and interfacial Maxwell–Wagner–Sillars (MWS) polarization. Local relaxations follow Arrhenius behavior and their time scale is not affected by the soft segment molecular weight. α-Relaxation follows Vogel–Tammann–Fulcher (VTF) behavior and is slower for the copolymer based on PEO-4600. Conductivity relaxation and the interfacial MWS polarization also follow VTF behavior and have quite similar slopes since both are related to the same phenomena. Unexpectedly, the interfacial MWS polarization is not affected by the soft segment molecular weight. Although this result suggests that the soft segment molecular weight does not affect the microphase separation in these copolymers, we believe that no safe conclusions can be extracted for this system due to the high complexity and the presence of many phases with different conductivity. However, significant differences were observed in the conductivity relaxation, which is much faster for the copolymer based on PEO-2000, due to its lower crystallinity when compared with others.

Low Density Polypropylene/Waste Cellulose Fiber Composites by High-Shear Thermo-Kinetic Mixer

Abstract Achieving an appreciable weight reduction in PP based composite materials, particularly the ones reinforced by glass fibers, is quite challenging while enhancing their mechanical properties and fullfilling other enviromental concerns. To address this issue, low density composites of Poly(propylene) (PP) and waste cellulose fibers (WCF) were produced by high-shear thermo-kinetic mixer. This technique facilitates the ease of processing for the mass production of such composite materials due to the availability of high shear rates and relatively short processing times during manufacturing. The structure-property behavior of the molded samples was investigated as a function of WCF content. Briefly, one-fold increase in elastic modulus, 18 % increase in tensile strength, 87 % increase in flexural modulus and 27 % increase in flexural strength of PP were achieved by the addition of 30 wt.% WCF. The significant enhancements in mechanical properties were mainly attributed to the homogeneous dispersion of intrinsically stiff WCF filler in the PP matrix as a direct result of the high-shear mixing. These results mainly suggest that waste cellulose fibers can be used as an effective reinforcing agent in PP matrix instead of highly dense, non-renewable and non-biodegradable fibers, such as glass fibers, that prevents further stresses on the environment. Along with this, the reuse of waste cellulose fiber in PP matrix, particularly at high concentrations like 30 wt.%, evenly corresponds to the reduction of total PP consumption for PP based composite production. The main conclusion of the study is that the extensive blending technology gives us the ability to produce high performance thermoplastic based composite materials as well as addressing the world-wide waste disposal problem by reusing of natural wastes, which is a great opportunity to ensure sustainability and reduce enviromental and economical costs for many industries.