Surface modification of polyethylene with multi-end-functional polyethylene additives

Influence of PVAc/PVA Hydrolysis on Additive Surface Activity

This aims to establish design rules for the influence of complex polymer matrices on the surface properties of small molecules. Here, we consider the dependence of the surface behaviour of some model additives on polymer matrix hydrophobicity. With stoichiometric control over hydrolysis, we generate systematic changes in matrix chemistry from non-polar, hydrophobic PVAc to its hydrolysed and hydrophilic analogue, PVA. With the changing degree of hydrolysis (DH), the behaviour of additives can be switched in terms of compatibility and surface activity. Sorbitol, a polar sugar-alcohol of inherently high surface energy, blooms to the surface of PVAc, forming patchy domains on surfaces. With the increasing DH of the polymer matrix, its surface segregation decreases to the point where sorbitol acts as a homogeneously distributed plasticiser in PVA. Conversely, and despite its low surface energy, octanoic acid (OA) surprisingly causes the increased wettability of PVAc. We attribute these observations to the high compatibility of OA with PVAc and its ability to reorient upon exposure to water, presenting a hydrophilic COOH-rich surface. The surfactant sodium dodecyl sulfate (SDS) does not show such a clear dependence on the matrix and formed wetting layers over a wide range of DH. Interestingly, SDS appears to be most compatible with PVAc at intermediate DH, which is consistent with the amphiphilic nature of both species under these conditions. Thus, we show that the prediction of the segregation is not simple and depends on multiple factors including hydrophobicity, compatibility, blockiness, surface energy, and the mobility of the components.

Modification of Polyethylene by RF Plasma in Different/Mixture Gases

Herein, low-density polyethylene (LDPE) films were treated using radio-frequency plasma discharge in the presence of air, nitrogen, oxygen, argon, and their mixtures to introduce new chemical functionalities. The surface properties of treated LDPE were qualitatively and quantitatively characterized using various analytical and microscopic techniques. It was found that the optimum plasma treatment for LDPE occurs in the presence of air plasma at an exposure time of 120 s and 80 W of nominal power. The plasma formed layer had tendency to increasing thickness with increasing treatment time up to 60 s using air and oxygen and even more with inert gases. An aging study of plasma-treated LDPE samples stored in ambient air or water medium revealed the partial hydrophobic recovery.

Toward a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellency of Polyethylene Terephthalate (PET) Films Modified with Perfluoropolyether-Based Polyesters

Original perfluoropolyethers (PFPE)-based oligomeric polyesters (FOPs) of different macromolecular architecture were synthesized via polycondensation as low surface energy additives to engineering thermoplastics. The oligomers do not contain long-chain perfluoroalkyl segments, which are known to yield environmentally unsafe perfluoroalkyl carboxylic acids. To improve the compatibility of the materials with polyethylene terephthalate (PET) we introduced isophthalate segments into the polyesters and targeted the synthesis of lower molecular weight oligomeric macromolecules. The surface properties such as morphology, composition, and wettability of PET/FOP films fabricated from solution were investigated using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. It was demonstrated that FOPs, when added to PET film, readily migrate to the film surface and bring significant water and oil repellency to the thermoplastic boundary. We have established that the wettability of PET/FOP films depends on three main parameters: (i) end-groups of fluorinated polyesters, (ii) the concentration of fluorinated polyesters in the films, and (iii) equilibration via annealing. The most effective water/oil repellency FOP has two C₄F₉-PFPE-tails. The addition of this oligomeric polyester to PET allows (even at relatively low concentrations) reaching a level of oil repellency and surface energy comparable to that of polytetrafluorethylene (PTFE/Teflon). Therefore, the materials can be considered suitable replacements for additives containing long-chain perfluoroalkyl substances.

Predicting oligomer/polymer compatibility and the impact on nanoscale segregation in thin films

Compatibility between oligomers and polymers was systematically assessed using differential scanning calorimetry (DSC) and was correlated with similarity in saturation and solubility parameter. These measurements enabled validation of detailed volume of mixing calculations using Statistical Association Fluid Theory (SAFT-γ Mie) and molecular dynamics (MD) simulations, which can be used to predict behaviour beyond the experimentally accessible conditions. These simulations confirmed that squalane is somewhat more compatible with poly(isoprene), "PI" than poly(butadiene), "PB", and further enabled prediction of the temperature dependence of compatibility. Surface and interfacial segregation of a series of deuterated oligomers was quantified in rubbery polymer films: PI, PB and hydrogenated poly(isoprene) "hPI". A striking correlation was established between surface wetting transition and mixtures of low compatibility, such as oligo-dIB in PB or PI. Segregation was quantified normal to the surface by ion beam analysis and neutron reflectometry and in some cases lateral segregation was observable by AFM. While surface segregation is driven by disparity in molecular weight in highly compatible systems this trend reverses as critical point is approached, and surface segregation increases with increasing oligomer molecular weight.

Surfactant and Plasticizer Segregation in Thin Poly(vinyl alcohol) Films

The vertical depth distributions of individual additive components [cetyltrimethylammonium bromide (CTAB), deuterated pentaethylene glycol monododecyl ether (d25-C12E5), and deuterated glycerol (d-glycerol)] in PVA films have been isolated and explored by ion beam analysis techniques and neutron reflectometry. The additives display an unexpectedly rich variety of surface and interfacial behaviors in spin-cast films. In separate binary films with PVA, both d-glycerol and CTAB were evenly distributed, whereas d25-C12E5 showed clear evidence for surface and interfacial segregation. The behavior of each surfactant in PVA was reversed when the plasticizer (glycerol) was also incorporated into the films. With increasing plasticizer content, the surface activity of d25-C12E5 systematically decreased, but remarkably, when glycerol and CTAB were present in PVA, the surface and interfacial activities of CTAB increased dramatically in the presence of glycerol. Quantification of the surface excess by ion beam analysis revealed that, in many cases, the adsorbed quantity far exceeded what could reasonably be explained by a single layer, thus indicating a wetting transition of the small molecules at the surface or interface of the film. It appears that the surface and interfacial behaviors are partly driven by the relative surface energies of the components, but are also significantly augmented by the incompatibility of the components.

Fluorine-Enriched Melt-Blown Fibers from Polymer Blends of Poly(butylene terephthalate) and a Fluorinated Multiblock Copolyester

Melt-blown fibers (dav ∼1 μm) were produced from blends of poly(butylene terephthalate) (PBT) and a partially fluorinated random multiblock copolyester (PFCE) leading to enhanced hydrophobicity and even superhydrophobicity (static water contact angle = 157 ± 3°) of the associated fiber mats. XPS measurements demonstrated quantitatively that the surface fluorine content increased systematically with the bulk loading of PFCE, rising to nearly 20 atom %, which corresponds to 41 wt % PFCE at a bulk loading of 10 wt %. The PBT/PFCE fibers exhibit greater fluorine surface segregation than either melt-blown PBT/poly(ethylene-co-chlorotrifluoroethylene) (PBT/PECTFE) fibers or electrospun fibers obtained from blends of poly(styrene) and fluoroalkyl end-capped polystyrene (PS/PSCF). Dynamic contact angle measurements further demonstrated decreased surface adhesion energy of the melt-blown PBT/PFCE fiber mats due to the blooming of PFCE to the surface.

New type of thermoplastic bio composite: nature of the interface on the ultimate properties and water absorption

A new type of thermoplastic bio composite with coir fibre derived from coconut was fabricated by means of plasma modification of the polymer surface.