Helen Hassander

Improved compatibility between polyamide and polypropylene by the use of maleic anhydride grafted SEBS

Abstract Blends containing equal weight fractions of polypropylene (PP) and polyamide (PA-6 and PA-6.6) and up to 25% of a compatibilizing thermoplastic elastomer, either polystyrene-block-poly(ethylene-stat-butylene)-block-polystyrene (SEBS) or SEBS modified by maleic anhydride (SEBS-MA), were prepared by melt mixing. In all these blends, PP formed the continuous matrix phase. Even at high concentrations, unmodified SEBS was found to be a poor compatibilizer, affecting mainly the properties of the matrix. The graft copolymer formed, by reaction between SEBS-MA and polyamide during melt mixing, strongly influenced the blend morphology, by forming an interphase, separating the PA phase domains from the matrix. The crystallization behaviour of PP indicated that full coverage required between 3% and 5% SEBS-MA at the intense mixing conditions used. Above this level, the total surface area of the polyamide domains seemed to increase in direct proportion to the concentration of SEBS-MA. The thickness of the interphase layer was estimated to be about 15xa0nm. At high concentrations of SEBS-MA, the PA domains agglomerated and formed extended structures held together by the interphase polymer. This was reflected by the stress–strain and rheological behaviour of the blends. In blends with PA domains of small volume, crystallization of PA was delayed. The rate of water absorption was very low in blends containing SEBS-MA, much lower than in corresponding blends containing SEBS.

The mechanism of emulsion stabilization by small silica (Ludox) particles

Abstract Small silica particles of the Ludox type, when combined with a costabilizer, can be used to stabilize fine droplet sized oil-in-water emulsions, having an excellent stability towards coalescence. The stabilization mechanism involves two steps; (i) agglomeration of the silica particles and (ii) adsorption of agglomerates of silica particles at the oil/water interface. The high emulsion stability is due to the presence of multiple silica particle layers around the droplets. The role of the costabilizer is to induce silica particle agglomeration. Silica particle aggregates seem to adsorb spontaneously at the oil/water interface irrespective of their charge density or structure. The important role of agglomeration in emulsion stabilization by small particles is discussed with reference to the practice and theory of fine particle flotation.

Bone cement with reduced proportion of monomer in total hip arthroplasty: Preclinical evaluation and randomized study of 47 cases with 5 years' follow-up

Bone cement with reduced amount of monomer and low curing temperature may improve implant fixation due to reduced toxicity. We analyzed the mechanical, chemical and thermal properties of such a cement (Cemex Rx) using Palacos R as control. The in vivo performance of the 2 cements was also evaluated in a prospective randomized study of 47 hips, where either of the cement types was used to fixate Lubinus SP2 prostheses with the stem made of titanium alloy. Cemex Rx had a reduced tensile strength, probably because this cement was manually mixed, as recommended by the manufacturer. A standardized laboratory test showed lower curing temperature for Cemex, but measurements at 37° and with prechilled Palacos R and Cemex Rx, as in clinical work, showed no difference. In the clinical study radiostereometric measurements of cup and stem migration showed similar values in the 2 groups up to 5 years after the operation. The cement mantle was stable in both groups, but the stems migrated similarly inside the cement mantle regardless of the type of cement used. Proximal wear was low (0.04-0.05 mm/year) and tended to be lower in the Cemex group (p = 0.02). Aluminum and vanadium levels in serum increased 5 years after the operation, but no difference was noted between the 2 groups. Collagen markers (PICP, ICTP) showed similar increases in bone turnover 6 weeks and 6 months after operation in both groups.

Effect of the mixing procedure on the morphology and properties of compatibilized polypropylene/polyamide blends

Abstract Blends containing equal amounts of polypropylene (PP) and polycaprolactam (PA6) were prepared by extrusion mixing, using 5% by weight of polystyrene-block-poly(ethylene-stat-butylene)-block-polystyrene, modified by grafting with maleic anhydride (SEBS-MA), as the compatibilizer precursor. The blends were obtained using three mixing procedures, representing different ways of introducing the compatibilizer. The blends were prepared by (A) one-step mixing of the three components, (B) mixing a preblend of SEBS-MA and PP with PA6, and (C) mixing a preblend of SEBS-MA and about one-third of the total amount of PA6 with PP and the rest of the PA6. All of the blends contained dispersed PA6 domains, surrounded by a separate interphase of the self-assembling compatibilizing polymer. The morphology of blends A and B were similar and markedly different from that of blend C, which contained dispersed phase domains of two clearly distinguishable populations. Impact strength and elongation at break were lowest for C. The poor performance of blend C is due to the fact that a considerable fraction of the compatibilizer ended up in small, well dispersed phase domains with a high weight ratio of compatibilizer to PA6.

Ion conductive electrolyte membranes based on co-continuous polymer blends

Solid electrolyte membranes based on comb-shaped poly(ethylene glycol) n(PEG) doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt in blends with poly(vinylidene fluoride-co-hexafluoropropylene) n(PVDF-HFP) have been studied. Membranes containing between 70 and 100 wt% PEG were prepared by a convenient two-step process where films containing a mixture of mono- and dimethacrylate-terminated PEG macromonomers, PVDF-HFP, LiTFSI, and a photoactivator were cast from acetone solutions, followed by UV-initiated polymerization of the macromonomers. Microscopy of the membranes revealed a phase separated morphology with a microporous PVDF-HFP network embedded in comb-shaped PEG. The membranes were thermally stable at temperatures below the melting point of PVDF-HFP at 140 °C. Dynamic mechanical analysis (DMA) in the tension mode showed that the mechanical properties of the membranes were greatly improved both by the addition of PVDF-HFP and of dimethacrylate-terminated PEG macromonomer. For example, the storage modulus at 25 °C and 1 Hz showed a three-fold increase after increasing the percentage of dimethacrylate-terminated PEG from 0 to 10 wt% in the macromonomer mixture. A broad shoulder on tan δ as a function of temperature indicated the existence of a PVDF-HFP rich amorphous interphase. At room temperature, the membranes containing more than 80 wt% PEG reached ionic conductivities exceeding 10−5 S cm−1.

Morphology of poly(isoprene‐co‐styrene‐co‐methacrylic acid) latex prepared by two‐stage seeded emulsion polymerization

Heterogeneous latexes were prepared by a two-stage seeded emulsion polymerization process at 80°C using potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier. Poly(styrene-co-methacrylic acid) latexes containing varying amounts of methacrylic acid (MAA) were used as seeds. The second-stage polymer was poly(isoprene-co-styrene-co-methacrylic acid). By using different methods for the addition of the MAA and by varying the amount of MAA, the hydrophilicity of the polymer phases could be controlled. The morphologies and size distributions of the latex particles were examined by transmission electron microscopy. The latexes were in all cases unimodal, and had narrow particle size distributions. The particles displayed different morphologies depending on the polymerization conditions and monomer composition. The hydrophilic properties of the two phases in combination with the internal particle viscosity and crosslinking of the second phase during polymerization were found to be the major factors influencing the particle morphology.

On the macro‐ and microphase separation of compatibilizers in immiscible polymer blends

Macro- and microphase separation of compatibilizing graft copolymers in melt-mixed polystyrene/polyamide-6 blends was studied by transmission electron microscopy and thermal analysis. Three different graft copolymers with main chains of polystyrene and side chains of poly(ethylene oxide) were used as additives at various concentrations. The polyamide-6 domain sizes decreased with increasing amounts of compatibilizing graft copolymers in the blends up to a saturation concentration, after which no further reduction was noted. Macrophase separation of the graft copolymers into discrete macrodomains 20-200 nm in size occurred at concentrations equal to or slightly lower than the saturation concentration. The macrodomains of the graft copolymers were microphase separated, and the sizes and shapes of the microdomains were found to largely depend on the graft copolymer structure and composition. As a consequence of microphase separation, poly(ethylene oxide) crystallinity was noted in blends with sufficiently high macrophase contents. Observations of a graft copolymer interphase between the polystyrene matrix and the polyamide-6 domains confirmed that the graft copolymer was present at the blend interfaces in some of the compatibilized blends. (Less)

Influence of seed polymer molecular weight on polymerization kinetics and particle morphology of structured styrene–butadiene latexes

Heterogeneous film-forming latexes were prepared using two-stage, seeded emulsion polymerization. The polymerization was performed in a calorimetric reactor with a control unit that monitored the reaction rate and controlled the charging rate of the monomers. Three types of styrene seed latexes were prepared at 70°C. The first was an unmodified polystyrene (PS) latex. The second had the molecular weight lowered by the use of carbon tetrachloride (CCl4) as a chain-transfer agent, added at the start of the polymerization. For the third one, divinylbenzene (DVB) was used as a comonomer. DVB was added under starved conditions near the end of the polymerization to achieve crosslinked particle shells and to introduce double bonds as possible grafting sites. The second polymerization step was performed at 80°C as a batch operation in a 200-mL calorimeter reactor. The second-stage polymer was poly(styrene-co-butadiene-co-methacrylic acid) (S/B/MAA). A fixed S/B ratio was used together with varying small amounts of MAA. Particle morphology and particle-size distributions were examined after the second stage using TEM after staining with osmium tetroxide. The particle morphology was found to depend on both the seed composition and the amount of MAA used in the second stage. Molecular weight and crosslinking of the DVB-containing seed influenced the internal particle viscosity, which gave differences in the polymerization rate and the particle morphology. Crosslinking of the second-stage polymer decreased the monomer concentration in the particles, which could be detected as a change in the slope the pressure/conversion curve. This phenomenon was used to indicate the critical conversion for crosslinking of the second-stage polymer.

Flocculation of PVC Latex Particles in the Presence of Vinyl Chloride

A study has been carried out to elucidate the mechanism of a process by which a polyvinyl chloride (PVC) resin in powder form is obtained by flocculation of a PVC latex in the presence of liquid vinyl chloride monomer (VCM). The steps in the process were: n n1. n naddition of a flocculating polymer to the latex, n n n n n2. n naddition of VCM under thorough stirring, and n n n n n3. n nevaporation of VCM.