Ivan Kelnar

Reactive blending of nylon 6 and modified poly(styrene‐co‐maleic anhydride); influence of poly(styrene‐co‐maleic anhydride) modification by fatty amine onto blend properties

Blends of PA 6 with SMA or with 12.5–100% fatty amine (C 18) modified SMA at compositions 95/5–60/40 were studied. Particle size of SMA dispersed in PA 6 matrix was around 0.1 μm due to in situ compatibilizer formation. The strength and stiffness of the blends were higher and toughness unchanged in comparison with PA 6 values. Microscopic observations confirm that improvement of mechanical properties of PA 6 by addition of brittle SMA is due to plastic deformation of SMA particles that consume significant amounts of deformational energy. This cold drawing is caused by compressive stress evolved by bulk deformation; this stress should exceed the critical brittle-to-ductile fracture mode transition. In the blends studied, cold drawing apparently occurred when the developed stress was lower than the critical one. It is concluded that a very fine phase structure with an apparently strong interface makes the plastic deformation of dispersed SMA easier.

Carboxymethylated-, hydroxypropylsulfonated- and quaternized xylan derivative films.

Under alkaline/water conditions carboxymethyl, 2-hydroxypropylsulfonate and trimethylammonium-2-hydroxypropyl groups were introduced into xylan in one step with the goal to prepare film specimens. The materials were characterized by NMR, SEC-MALS, TG/DTG/DTA, AFM and mechanical testing. The properties of triple, double and mono-substituted materials were compared. The numerical molar masses of the specimens were from 12.3 to 17.6 kg/mol with Mw/Mn from 1.27 to 1.34. The elastic modulus values are decreasing in order: xylan (X; 7354 MPa)>carboxymethyl xylan (CX; 6090MPa)>2-hydroxypropylsulfonate xylan (SX; 6000 MPa)>carboxymethyl/2-hydroxypropylsulfonate xylan (CSX; 4490 MPa)>quaternized xylan (QX; 3600 MPa)>carboxymethyl/quaternary/2-hydroxypropylsulfonate xylan (CQSX; 3380 MPa)>carboxymethyl/quaternary xylan (CQX; 2805 MPa). The onset temperatures of SX (214°C), CQSX (212°C), QSX (211°C) and CQX (207°C) were higher than for X (205°C). The roughness values of the film surfaces (3.634-18.667 nm) are higher on top than on the bottom of the specimen.

Effect of layered silicates and reactive compatibilization on structure and properties of melt-drawn HDPE/PA6 microfibrillar composites

Microfibrillar composites (MFCs) of HDPE matrix with PA6 reinforcing fibrils formed in situ by melt drawing were modified by ethylene/glycidyl methacrylate copolymer (PEGMA) and addition of layered silicates using different mixing protocols. The goal was enhancement of adhesion between fibrils and matrix, their reinforcement by clay, and evaluation of the effect of clay on the MFC morphology, especially the fibril dimensions. Improved mechanical properties, including toughness, were found in the case of pre-blending Cloisite 15A (C15) with both polymeric components. Pre-blending of Cloisite C30B (C30) in PA6 is effective at low draw ratios only, whereas simultaneous addition of both clays leads to significant worsening of properties. In many cases, low stiffness increase indicates existence of clay-induced controversial effects which may eliminate reinforcement induced by fibrils and clay. The results indicate that these effects are significantly affected by the extent and course of clay migration between polymer phases during extrusion-mixing and melt drawing. Possible explanation of affecting the properties due to low-modulus interface supported by finite element analysis (FEA) is presented.

Crystallization and thermal properties of melt-drawn PCL/PLA microfibrillar composites

Abstract Microfibrillar composites (MFC) are advanced systems with reinforcement formed in situ by melt or cold drawing of suitable polymer blends. In the case of biodegradable poly (ɛ-caprolactone)/poly (lactic acid) (PCL/PLA) system, formation of microfibrillar structure by melt drawing is only possible by modification of the polymer components by clay. The effect of clay is quite complex; this study is focused on the effect of in situ formed fibrillar structure of PLA and clay in MFC with the PCL matrix on crystallinity and glass transition of both polymer components. The DSC analysis shows that clay addition to neat PCL, its blending with PLA, and addition of clay to the PCL/PLA blend increase PCL crystallinity. Clay addition and blending with PCL dramatically increase crystallinity of originally almost amorphous PLA. The non-isothermal PCL crystallization kinetics evaluated by the new recently proposed method reveals pronounced nucleation effect of clay addition and blending on PCL crystallization. An indication has been found of a negative correlation between maximum crystallization rate of PCL and its crystallinity. The glass transition temperature Tg of both components evaluated by DMA in the undrawn system mostly decreases with clay addition and increases with drawing. These effects are more significant for PLA due to its fibrillar structure. Tg is affected by the mixing protocol, as a result of different course of clay migration between components and localization, especially in the interfacial area.

Quaternized and sulfated xylan derivative films

Xylan quaternized sulfate films were prepared from beech xylan (X) and compared with fully sulfated xylan films (XS). When quaternized xylan (QX) was prepared in the first step (DS(Q)=0.55), than by sulfation of QX in the second step the fully substituted ampholytic derivative (QXS; DS(Q)=0.33; DS(S)=1.67) could be obtained. By sulfation in first step, xylan sulphate (SX, DS(S)=0.70) was obtained and by subsequent quaternization, SXQ film with DSQ=0.55 and DSS=0.33 which contained partially unsubstituted hydroxyls. The molar masses (M(n)) of the films soluble parts were increasing in order X<SX<SXQ<QX<XS<QXS. In all films there were some insoluble particles present as determined by the amount of recovered masses by SEC-MALS. The materials were further characterized by AFM, XRD, TG/DTG/DTA, NMR and mechanical testing. QXS and SXQ could form mechanically more stable films than XS specimens.

Ternary reactive blends of nylon‐6 matrix with dispersed rigid brittle polymer and elastomer

Except by elastomers, the toughness of nylon-6 (N-6) can be improved by the addition of rigid poly(styrene-co-maleic anhydride) (SMA). In this case, strength and stiffness are also enhanced. Combination of SMA with maleated ethylene-propylene rubber or styrene-ethene/butene-styrene with a total content below 15% gives a ternary blend having a toughness level close to elastomer toughening, whereas the strength and stiffness reached at least the Nylon-6 values. An explanation is a synergistic combination of both elastomer and rigid polymer toughening mechanisms. An opposite effect on mechanical behavior was found with high contents of both additives. Except for worsened strength and stiffness, in some cases, a higher elastomer content even did not enhance the toughness. This effect can be explained by too fine phase structure found, causing the matrix ligament dimension to be below its minimum critical value.

The effect of urea and urea-modified halloysite on performance of PCL

The effects of urea and urea-modified halloysite nanotubes (HNT) on structure and properties of poly(ɛ-caprolactone) (PCL) were evaluated using mechanical testing combined with FTIR, DSC, DMA, and various microscopic techniques. The results indicate important changes in mechanical behavior by urea-mediated interchain hydrogen bonding in PCL, whereas no linking between PCL and HNT in the related nanocomposite was found. As a result, the improved mechanical behavior of nanocomposites with urea-modified HNT was caused by combination of the matrix modification and urea-aided enhanced dispersion of HNT. The additives do not have any marked effect on PCL crystallinity. HNT increases and urea reduces the overall rate of crystallization. Both additives show a moderate nucleating effect.

Influence of the component reactivity on the properties of ternary reactive blends Nylon 6/rigid brittle polymer/elastomer

The ternary reactive blend of Nylon 6 matrix with dispersed poly(styrene-co-maleic anhydride) and maleated SEBS or EPR represents a toughened system with enhanced strength and, at least, the retained stiffness of the matrix. In the present work, the influence of changed reactivity of dispersed phases, including the application of one or both nonreactive components, on the phase structure and related mechanical behavior is studied. Lowering of the reactivity of the elastomer caused a decrease of blend properties, whereas suitable dilution of SMA by PS brought better properties in comparison with a fully reactive system. With the nonreactive N6/PS/SEBS blend, the formation of blended bicontinuous inclusions causes worsening of toughness. This documents the importance of separate dispersion of both phases for good mechanical behavior in the system studied, which is shown to be assured by application of at least one reactive component.

Influence of clay-nanofiller geometry on the structure and properties of poly(lactic acid)/thermoplastic polyurethane nanocomposites

The effect of two clays with different geometries, viz. organophilized montmorillonite nanoplatelets (oMMT) and halloysite nanotubes (HNT), on the structure and properties of poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) 80/20 and 70/30 has been studied. The reinforcement of both the components and the blend is higher for oMMT due to its higher specific surface area and aspect ratio. The effect of both nanofillers (NFs) on the structure, reflected in a decrease of the dispersed TPU size, is comparable. A larger effect on the viscosity by oMMT is eliminated by its more marked less favourable localization in the dispersed phase in comparison with HNT. The fact that the toughness of the HNT-containing nanocomposite (NC) is markedly higher (with maximum at 1% HNT) than that with oMMT is in contradiction with PLA NC. The results indicate that the application of nanofillers can lead to a polymer system with a balanced mechanical behaviour. However, a different impact of NFs on the polymer components and interface parameters may also lead to antagonistic effects. The influence of NFs, including their geometry, on the polymer blend is more complex in comparison with single-matrix nanocomposites.

Graphite nanoplatelets-modified PLA/PCL: Effect of blend ratio and nanofiller localization on structure and properties

Structure and properties of poly(lactic acid) (PLA)/poly (ɛ-caprolactone) (PCL) influenced by graphite nanoplatelets (GNP) were studied in dependence on blend composition. Electron microscopy indicates predominant localization of GNP in PCL. GNP-induced changes in viscosity hinder refinement of PCL inclusions, support PCL continuity in the co-continuous system, and lead to reduction of PLA inclusions size without GNP being present at the interface in the PCL-matrix blend. Negligible differences in crystallinity of both phases indicate that mechanical behaviour is mainly influenced by reinforcement and GNP-induced changes in morphology. Addition of 5 parts of GNP leads to ~40% and ~25% increase of stiffness in the PCL- and PLA-matrix systems, respectively, whereas the reinforcing effect is practically eliminated in the co-continuous systems due to GNP-induced lower continuity of PLA which enhances toughness. Impact resistance of the 80/20 blend shows increase with 5 parts content due to synergistic effect of PCL/GNP stacks, whereas minor increase in the blend of the ductile PCL matrix with brittle PLA inclusions is caused by GNP-modification of the component parameters. Results indicate high potential of GNP in preparing biocompatible systems with wide range of structure and properties.