Surface Engineering of Microporous Polypropylene Membrane for Antifouling: A Mini-Review

The surface properties of polymer membranes are very important to their separation performance. It is generally accepted that a hydrophilic membrane surface is favorable for applications in water treatment and bioseparation, because the hydrophilic surface can enhance water permeate flux and mitigate membrane fouling. Microporous polypropylene membrane (MPPM) is a promising membrane material for membrane distillation and membrane gas–liquid contactor, due to the intrinsically high hydrophobicity of polypropylene. However, it is the hydrophobicity that severely limits the wider application of MPPM in aqueous solutions and biomedical fields. Surface hydrophilization is, therefore, logically necessary. Surface engineering of polymer membranes encompasses those processes which modify the membrane surfaces to confer different properties to those of the bulk and thus improve their in-service performance. This review provides a concise summary and discussion of the surface engineering strategies developed in our laboratory and reported in scientific literature, which aim at enhancing the surface hydrophilicity and antifouling property of MPPM.     

35—THE SETTING OF WOOL: ENHANCEMENT BY THE INTRODUCTION OF BULKY GROUPS

An account is given of the setting behaviour of wool fabrics after treatment with a variety of anhydrides of carboxylic acids. The incorporation of relatively large numbers of small acyl groups had little effect on the settability, but bulky acyl groups caused a large enhancement. Unlike untreated wool, wool containing large numbers of bulky acyl, e.g., benzoyl, groups can be steam-set extremely readily without any need for prior wetting.

From a detailed study of the setting behaviour and set stability of benzoylated fabric, it was concluded that two main types of interaction were involved, namely, electrostatic and hydrophobic interactions. Electrostatic interactions were believed to predominate at low levels of acylation, the result being inhibition of set. These were outweighed by hydrophobic interactions at higher levels of acylation with bulky anhydrides, which resulted in set stabilization. Disulphide-bond rearrangements appear to play little part in the setting of wools with high contents of bulky acyl groups.     

The effect of atmospheric pressure helium plasma treatment on the surface and mechanical properties of ultrahigh-modulus polyethylene fibers

Ultrahigh-modulus polyethylene fibers were treated with atmospheric pressure He plasma on a capacitively coupled device at a frequency of 7.5 kHz and a He partial vapor pressure of 3.43 × 10³ Pa. The fibers were treated for 0, 1, and 2 min. Microscopic analysis showed that the surfaces of the fibers treated with He plasma were etched and that the 2-min He plasma-treated group had rougher surfaces than the 1-min He plasma-treated group. XPS analysis showed a 200% increase in the oxygen content and a 200% increase in the concentration of C—O bonds (from 11.4% to 31%) and the appearance of C=O bonds (from 0% to 7.6%) on the surface of plasma-treated fibers for the 2-min He plasma-treated group. In the microbond test, the 2-min He plasma-treated group had a 100% increase of interfacial shear strength over that of the control group, while the 1-min He plasma-treated group did not show a significant difference from the control group. The 2-min He plasma-treated group also showed a 14% higher single-fiber tensile strength than the control group.     

Investigation on wetting behaviour of B4C by Ni based brazing alloys

Abstract

In the present study, the wetting behaviour of boron carbide by Ni based brazing alloys has been investigated. Based on the results of wetting experiments using sessile drop method, it has been revealed that these filler metals are generally able to wet B₄C surface. This relates to the reactivity of Ni with this ceramic material. The presence of Si in these fillers and its reactivity with the surface of B₄C play a major role in wetting improvement. In addition, the existence of Cr in the filler also improves this behaviour. Based on the results of wetting tests, a low wetting angle of 26° was obtained for the filler metal having the highest amounts of Si and Cr. In this article, the microstructure and chemical composition of the interfacial phases have been studied.     

Investigation of load transfer between the fiber and the matrix in pull-out tests with fibers having different diameters

Single-fiber pull-out tests were used for investigation of the interfacial bond strength or toughness and load transfer between polymeric matrices and glass fibers having different diameters. The interfacial bond strength was well characterized by an ultimate interfacial shear strength (τ_ult) whose values were nearly independent of the fiber diameter. The same experiments were also analyzed by fracture mechanics methods to determine the interfacial toughness (G_ic). The critical energy release rate (G_ic) was a good material property for constant fiber diameter, but G_ic for initiation of debonding typically became smaller as the fiber diameter became larger. It was also possible to measure an effective shear-lag parameter, β, characterizing the load transfer efficiency between the fiber and the matrix. β decreased considerably with the fiber radius; this decrease scaled roughly as expected from elasticity theory. The measured results for β were used to calculate the radius of matrix material surrounding the fiber that was significantly affected by the presence of the fiber. The ratio of this radius to the fiber radius (R_m/r _f) was a function of the fiber diameter.     

Modelling of viscoelastic coextrusion flows in multi-manifold flat dies

Abstract

A recently proposed modification of the viscoelastic Leonov model is employed as a stress calculator in FEM analysis with a full u-v-p-t numerical scheme for coextrusion flow in multimanifold flat dies with 30° and 90° entrance angles. It is shown that the predicted stresses, interface location and streamline fields are in good agreement with the measurements. It is also shown that extensional viscosity has to be used in the modelling of the coextrusion flow to confirm experimental data.     

The effect of liquid-induced adhesion changes on the interfacial shear strength between self-assembled monolayers

Friction between chemically-modified tips and surfaces has been studied with chemical force microscopy (CFM) to evaluate the effect of changing solid/liquid free energy on energy dissipation in sliding tip-surface contact. Well-controlled conditions were necessary to attain a single asperity contact in these experiments. We found that in a series of methanol- water mixtures the interfacial shear strength between CH3-terminated surfaces of the siloxane self-assembled monolayers (SAMs) was independent of the adhesion force. The shear strength value of 10.2 ± 1.0 MPa found for this interface under methanol-water media is consistent with the previous studies of similar systems under dry gas conditions. A comparison to available data on interfacial shear strengths demonstrated that siloxane monolayers were much more effective in reducing friction than various carbon coatings.     

Inorganic interfacial engineering: processing of hard materials

Abstract

Inorganic interfacial engineering may be regarded as the core of powder metallurgical processing of hard materials. The present paper reviews recent results from an interdisciplinary research effort, BRIIE (the Brinell Centre for Inorganic Interfacial Engineering), a joint effort between five industrial companies, three universities, two research institutes and VINNOVA (the Swedish Agency for Innovation Systems). The research involves experimental work on the aqueous processing of powders and the use of surface actants is reviewed as well as the colloidal processing of ceramics. Pressing and sintering of agglomerated powders have been studied both theoretically and experimentally. Models for the simulation of pressing and sintering of hard metal powders are developed. Results on ceramic materials obtained by spark plasma sintering and their resistance to thermal shock are reported.     

12—THE FORMATION OF LYSINOALANINE AND LANTHIONLNE IN WOOL FIBRES STRETCHED IN BOILING WATER,AND THEIR RELATION TO PERMANENT SET

When wool fibres are held at 40% extension in boiling water for increasing periods of time, there is a progressive decrease in their cystine contents with concomitant increases in their lanthionine and lysinoalanine contents. After 3 hr, the contents of these amino acids have reached a maximum, which coincides with the maximum retention of set. At this time, approximately 24% of the cystine residues have been modified.

The mechanism of set is a complex phenomenon involving conformational changes in the proteins constituting the microfibril–matrix structure of the wool fibre. Whereas the results in this paper support the cross-linkage-stabilization theory of set postulated by Speakman, their implications, both for this and for the thiol–disulphide-interchange theory of set, are discussed in the light of modern ideas on the structure of wool.     

13—CELLULOSIC COMPOSITE FIBRES

An account is given of an investigation in which gross particles consisting of either jute or viscose rayon fibres of different lengths and diameters were spun in both secondary cellulose acetate filaments and a polyurethane elastomer in order to verify whether a significant degree of reinforcement was possible with a composite material of this type. The mechanical properties of the composite cellulose acetate fibres were studied, and it is shown that both types of filler produced a decrease in breaking extension and an increase in initial modulus with increasing filler content. The strength of the jute-filled material is also shown to increase. Similar effects on the breaking extension and initial modulus of the rayon-filled polyurethane filaments were observed, and here there was also a decrease in strength that arose from the difference in extensibility between the rayon and the polyurethane filament.