Morphologies and mechanical properties of polyarylate/liquid crystalline polymer blends compatibilized by a multifunctional epoxy resin

The tetrafunctional epoxy resin, tetraglycidyl‐4′,4′‐diaminodiphenyl methane (TGDDM), has been investigated as an efficient reactive compatibilizer for the blends of polyarylate (PAr) with a liquid crystalline polymer (LCP). TGDDM can react with PAr and LCP at the interface simultaneously to produce the PAr‐co‐TGDDM‐co‐LCP mixed copolymers during melt blending. These copolymers tend to anchor along the interface as the result of the interfacial reaction and thus serve as effective compatibilizers to reduce the interfacial tension and to enhance the interfacial adhesion in the solid state. The morphologies of the PAr/LCP blends were inspected by means of scanning electron microscopy (SEM). It is observed that the dispersed LCP phase domains reduce obviously after compatibilization. Furthermore, it is also found that the reduced interfacial tension caused by the addition of TGDDM plays a vital role in affecting the deformation of the LCP phase domains in the compatibilized PAr/LCP blends. The LCP phase tends to deform into greater numbers and finer fibrils with high aspect ratio after the addition of TGDDM in those blends containing adequate LCP content (> 10 %). In the blend containing low amount of LCP (Par / LCP = 95/5) with high TGDDM content (0.3 phr or higher), however, the LCP phase can only exist as fine but short fibrils or even ellipsoids. The overall mechanical properties of the PAr/LCP blends are substantially improved after compatibilization by this coupling‐type reactive compatibilizer. The generation of LCP fibrils with high aspect ratio and improved interfacial adhesion are the two hinges to enhance the performance of the compatibilized PAr/LCP blends.     

Evolution of the Morphology and Characterization of Compatibilized PBT/EVA Blends Prepared by Reactive Extrusion

Summary: In this work, the possibility of preparing compatibilized blends of poly(butylene terephthalate) (PBT) and an ethylene vinyl acetate (EVA) copolymer by reactive extrusion in the presence of an ethylene acrylic acid copolymer (EAA) and a bisoxazoline compound (PBO) as compatibilization promoters has been studied. In addition, the evolution of the morphology of the blends under different annealing conditions in the presence and absence of the compatibilizing promoters has been studied. Binary blends of PBT and EVA showed behavior typical of incompatible blends with a gross morphology and bad mechanical performance. The situation was however different for ternary PBT/EVA/EAA and especially for quaternary PBT/EVA/EAA/PBO blends. In the latter case, the morphology was finer, the adhesion improved and the mechanical properties were enhanced, with values almost doubled with respect to those of uncompatibilized blends. These results can be explained by the formation of in situ EAA‐g‐(PBO)PBT copolymers which act as compatibilizers for the blends. While the binary and, to some extent, the ternary blend display coalescence under annealing with rapid coarsening of the morphology, the quaternary compatibilized blends showed the best morphological stability as the particle dimensions remained practically unchanged. This phenomenon was interpreted considering the role of kinetic hindrance played by the compatibilizer formed in situ.

SEM micrograph of PBT/EVA/EAA/PBO blend at 5 000×.     

Effect of PP-g-LCP compatibilizer on the structure and crystallization of blends of isotactic polypropylene (PP) with a semiflexible liquid crystalline polymer (LCP)

Blends of i-polypropylene and a semiflexible liquid crystalline polymer (iPP/LCP 90/10 and 80/20 w/w) were compatibilized with 2.5, 5 or 10 wt.-% PP-g-LCP copolymers. The crystal structure, crystallization behaviour and morphology of the compatibilized blends have been investigated by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and optical microscopy. It is shown that the nucleation rate and crystallization rate of iPP strongly increased in the compatibilized blends in comparison to the uncompatibilized ones. In compatibilized blends, while iPP spherulites get smaller and crystallinity degree increases, the crystal growth mechanism of iPP remains unchanged. An assumption has been made about the mechanism of the compatibilization, using graft copolymers constructed of segments identical to the blended polymers: the PP segments of PP-g-LCP copolymers, if long enough, cocrystallize with bulk iPP, compatibilizing partially the two components; the LCP grafts of the copolymers cocrystallize with the bulk LCP or enter the amorphous phase of the blends. The miscibility of each part of the copolymer compatibilizers with the corresponding bulk component of the blend leads to a reduction of the interfacial tension and to a strong reduction of the dimensions of dispersed LCP phase. The compatibilized iPP/LCP blends display improved crystallization kinetics, enhanced degree of crystallinity and improved interphase adhesion. Consequently, an improvement of the mechanical properties and rheological characteristics should be expected for these blends.     

Isothermal crystallization kinetics of compatibilized blends of polyolefines with a semiflexible liquid crystalline polymer

A study of the isothermal crystallization behaviour and an analysis of the kinetic parameters of compatibilized blends of polyolefines (isotactic poly(propylene) (iPP) and high density polyethylene (HDPE)) with a semiflexible liquid crystalline polymer (LCP) SBH 1:1:2 of Eniricerche, Italy are presented in this work. The compatibilizers are ad hoc synthesized graft copolymers of the liquid crystalline polymer grafted to functionalized poly(propylene) (PPAA) or polyethylene (PEox) – PP-g-SBH and PE-g-SBH copolymers, respectively. It has been established that the LCP dispersed phase in the blends plays a role in nucleation for the polyolefine matrix crystallization. This effect is more pronounced in the poly(propylene) matrix than in the polyethylene matrix, due to the lower crystallization rate of the former. The addition of PP-g-SBH copolymers (2.5–10 wt.-%) to 90/10 and 80/20 iPP/SBH (w/w) blends provokes a drastic increase of the overall crystallization rate of the iPP matrix and of the degree of crystallinity. Contrarily, the addition of PE-g-SBH copolymers (2.5–8 wt.-%) to 80/20 HDPE/SBH (w/w) blends almost does not change or only slightly decreases the PE overall crystallization rate. Moreover, the interpretation of the Avrami exponents indicates that the iPP crystallization mechanism in the compatibilized iPP/SBH blends remains unchanged only until a degree of conversion of 0.7 and changes above this value; the PE crystallization mechanism and the degree of crystallinity in the compatibilized HDPE/SBH blends do not alter. The results were interpreted in terms of some differences in the compatibilization mechanism and efficiency of both types of graft copolymers (PP-g-SBH and PE-g-SBH). The relationships between blend morphology and nucleation phenomena are discussed.     

Morphology and Properties of Novel Blends Prepared from Simultaneous In Situ Polymerization and Compatibilization of Macrocyclic Carbonates and Maleated Poly(propylene)

Summary: Nanoscale polymer blend morphologies, with a dispersed minor phase as small as 50 nm, have been prepared via the in situ polymerization of macrocyclic carbonates in the presence of a maleic anhydride poly(propylene) (mPP). This simple, versatile, low cost strategy successfully produced a well‐defined, stable two phase nanoscale morphology with a considerable improvement in the ultimate mechanical properties and strong resistance to hydrocarbon solvents such as methylene chloride. The effect of blend composition on the rate of polymerization of the macrocyclic carbonates was studied by considering the increase in torque during the mixing process in the batch mixer. The polymerization rate decreased considerably with increasing concentration of mPP in the blend due to the formation of graft copolymer of polycarbonate‐g‐poly(propylene) (PC‐g‐PP). The viscoelastic behavior of the pure polymer components was found to play no role in controlling the blend morphology and size of the dispersed nanoscale particles. The blend morphology could be controlled by the compatibilization of the blend components, possibly via in situ formation of a graft copolymer. In addition, the blend morphology was strongly influenced by the value of the rotation speed (rpm) or shear rate encountered during the processing of the blends, i.e., the larger the rpm value, the finer the observed blend morphology. Both DSC and DMA data showed evidence of partial miscibility of the polymer blend components. In addition, the DMA data confirmed a preferential dissolution of mPP in polycarbonate (PC) instead of dissolution of PC in mPP as evidenced by the shift of the α‐relaxation process of the PC‐rich phase to lower temperatures while the α‐relaxation process of the mPP was relatively unaffected regardless of the PC composition. The percentage of mPP dissolved in PC was evaluated from the reduction in the T_g value (obtained from DSC data) of PC in the blend using the Fox equation and was found to be consistent with the DMA data and preferential dissolution of mPP in PC.

STEM photograph of mPP/PC = 10/90 blend. The sample was prepared at 225 °C and 200 rpm.     

Compatibilization of high density polyethylene/polyisoprene blends with polyethylene/polyisoprene “thread-through” copolymers

The compatibilization of high density polyethylene (HDPE)/polyisoprene (PI) blends with polyethylene/polyisoprene (PE/PI) “thread-through” copolymers was investigated. The proliferating structure of PE/PI with segments chemically identical to HDPE and PI, respectively, is different from that of graft copolymers. Studies showed that the dispersed domain size in the blends was significantly reduced and interfacial adhesion was improved by the compatibilization action of the copolymer. In the differential scanning calorimetry (DSC) analysis, the crystallization peak of HDPE in the blends became broad with adding the copolymer and fractionated crystallization appeared in the HDPE/PI blend compatibilized with the copolymer at a weight ratio of 30/70 while it appeared in the blend without copolymer at a weight ratio of 20/80. DMA results showed that by adding the copolymer, both the glass transition temperature (T_g) of the PI component and the a- relaxation of HDPE shifted to lower temperature, demonstrating the enhanced penetration of the two components. Mechanical properties of the blends were improved, especially the elongation at break, by the presence of the copolymers. The characteristic yielding at the fractured surface of the blends compatibilized with the copolymer indicates the fractural behavior of the material changed from brittle to tough.     

Fiber reinforced calcium phosphate cements -- on the way to degradable load bearing bone substitutes?

Calcium phosphate cements (CPC) are well-established materials for the repair of bone defects with excellent biocompatibility and bioactivity. However, brittleness and low flexural/tensile strength so far restrict their application to non-load bearing areas. Reinforcement of CPC with fibers can substantially improve its strength and toughness and has been one major strategy to overcome the present mechanical limitations of CPC. Fiber reinforced calcium phosphate cements (FRCPC) thus bear the potential to facilitate the use of degradable bone substitutes in load bearing applications. This review recapitulates the state of the art of FRCPC research with focus on their mechanical properties and their biological evaluation in?vitro and in?vivo, including the clinical data that has been generated so far. After an overview on FRCPC constitutes and processing, some general aspects of fracture mechanics of reinforced cementitious composites are introduced, and their importance for the mechanical properties of FRCPC are highlighted. So far, fiber reinforcement leads to a toughness increase of up to two orders of magnitude. FRCPC have extensively been examined in?vitro and in?vivo with generally good results. While first clinical products focus on the improved performance of FRCPC with regard to secondary processing after injection such as fixation of screws and plates, first animal studies in load bearing applications show improved performance as compared to pure CPCs. Aside of the accomplished results, FRCPC bear a great potential for future development and optimization. Future research will have to focus on the selection and tailoring of FRCPC components, fiber-matrix compatibilization, integral composite design and the adjusted degradation behavior of the composite components to ensure successful long term behavior and make the composites strong enough for application in load bearing defects.     

Reactive compatibilization of HDPE/PET blends by glycidyl methacrylate functionalized polyolefins

Blends of high-density polyethylene (HDPE) and poly(ethylene terephthalate) (PET) in weight compositions of 20/80, 40/60, 60/40 and 80/20 were modified with glycidyl methacrylate functionalized polyolefins with the aim of improving the compatibility and in particular elongation and impact strength. The compatibilizers used were ethylene/glycidyl methacrylate copolymers (E/GMA) and ethylene/ethyl acrylate/glycidyl methacrylate terpolymers (E/EA/GMA) with variable contents of reactive functions (1 to 8 wt.-% of glycidyl methacrylate). The effects of the compatibilizers were evaluated by studying the mechanical properties and the morphology of the blends. The addition of 5 wt.-% of functionalized polyolefins was found sufficient to improve ductility and impact strength of all compositions. A more pronounced compatibilizing effect was obtained with the functionalized terpolymer containing the smallest amount of glycidyl methacrylate. With this emulsifying agent, elongation at break is increased by a factor of four for the compositions near the inversion of phases. However, the main interest of this work is that it provides a compatibilization of immiscible blends of polyolefin and polyester by injection moulding. This melt processing is very interesting from an industrial point of view because it proves that materials with good mechanical properties can be obtained in one step of processing.     

On the Preparation and Characterization of Polyethylene/Polyamide Blends by Melt Processing in the Presence of an Ethylene/Acrylic Acid Copolymer and of New Phosphazene Compounds

Summary: Samples of HDPE and PA6 have been melt‐processed in the presence of two new phosphazene compounds, CP‐2EPOX and CP‐2OXA together with an ethylene/acrylic acid copolymer. The blends have been prepared in an industrial twin‐screw extruder by using PA6 and PE in weight ratios of 25/75 and 75/25. When used, 5 phr of EAA and 0.2 phr of CP have been added. The materials have been completely characterized from a rheological, morphological, and mechanical point of view. The results indicate that the additives used caused an increase in the rupture tensile properties, of the impact strength and viscosity especially in the PE‐rich blend in the presence of CP‐2EPOX. This result can be attributed both to a chain extension reaction on EAA and PA6 phases and on compatibilization effect due to the possible formation of EAA‐g‐PA6 copolymers. This latter occurrence is suggested by an improved adhesion between the phases and by an increased turbidity observed in the Molau tests. Between the two compatibilizers, the CP‐2EPOX displays the overall best results, especially for the PE‐based blends.

SEM micrograph of the PA6‐based binary blend.     

Evaluation of an in situ chemically crosslinked hydrogel as a long-term vitreous substitute material

Currently there is no material that can be used as a long-term vitreous substitute, and this remains an unmet clinical need in ophthalmology. In this study, we developed an injectable, in situ chemically crosslinked hydrogel system and evaluated it in a rabbit model. The system consisted of two components, both based on multi-functional poly(ethylene glycol) (PEG) but with complementarily reactive end groups of thiol and active vinyl groups, respectively. The two components are mixed and injected as a solution mixture, react in vivo via the Michael addition route and form a chemically crosslinked hydrogel in situ. The linkages between the end groups and the backbone PEG chains are specially designed to ensure that the final network structure is hydrolysis-resistant. In the rabbit study and with an optimized operation protocol, we demonstrated that the hydrogel indeed formed in situ after injection, and remained transparent and stable during the study period of 9 months without significant adverse reactions. In addition, the hydrogel formed in situ showed rheological properties very similar to the natural vitreous. Therefore, our study demonstrated that this in situ chemically crosslinked PEG gel system is suitable as a potential long-term vitreous substitute.     

Analysis of ovarian teratomas for isochromosome 12p: evidence supporting a dual histogenetic pathway for teratomatous elements.

Teratomas are the most common germ cell tumor (GCT) of the ovary and include several types with a range of clinical behavior. As in testicular teratomas, they may be benign, malignant or a component of a mixed GCT. In the testis, data support separate pathogeneses for prepubertal and postpubertal teratomas, with derivation of the former from a nontransformed germ cell and the latter from differentiation of a nonteratomatous, malignant GCT. The absence of cytogenetic abnormalities (including isochromosome 12p (i(12p)) in mature ovarian teratomas suggests that they may be analogous to prepubertal testicular teratomas, but there are no data regarding genetic changes in the teratomatous components of ovarian mixed GCTs. We therefore studied the teratomatous components of six mixed GCTs of the ovary using fluorescence in situ hybridization (FISH) for i(12p). Six mixed GCTs of the ovary occurred in patients 4-33 years of age; all had teratomatous and yolk sac tumor components and three also contained foci of embryonal carcinoma. Using FISH with 12p telomeric and 12 centromeric probes, five of six (83%) cases had detectable i(12p) in their nonteratomatous components, and four of six (66%) in the teratomatous component. One of the two cases without demonstrable i(12p) in the teratomatous portion of the mixed GCT also did not have identifiable 12p abnormalities in other elements of the mixed GCT. By comparison, five pure, mature ovarian teratomas and three pure, immature ovarian teratomas showed no evidence of either i(12p) or other forms of 12p amplification. These findings support that teratoma in mixed ovarian GCTs has a different pathogenesis compared to pure teratoma of the ovary. Furthermore, the findings of i(12p) in both the teratomatous and nonteratomatous components of ovarian mixed GCTs supports that the teratoma derives from other components, similar to the situation in the testis.     

Plastic strains during stent deployment have a critical influence on the rate of corrosion in absorbable magnesium stents

Magnesium stents are a promising candidate in the emerging field of absorbable metallic stents (AMSs). In this study, the mechanical and corrosion performance of dog-bone specimens and a specific stent design of a magnesium alloy, WE43, are assessed experimentally in terms of their corrosion behaviour and mechanical integrity. It is shown that plastic strains that are induced in the struts of the stent during stent deployment have a critical influence in directing subsequent corrosion behaviour within the material. In addition, the deployment and scaffolding characteristics of the magnesium stent are elucidated and contrasted with those of a commercial stainless steel stent. The magnesium stent is found to support higher levels of cyclic strain amplitude than the stainless steel stent, even prior to degradation, and this may play a role in reducing in-stent restenosis. This study provides new insights into the experimental performance of a current AMS design and material whilst demonstrating the critical influence of plastic strain on the corrosion performance and scaffolding ability of an AMS.     

Fibronectin binding properties of bacteriologic petri plates and tissue culture dishes

With the aid of a monoclonal antibody-based ELISA assay, the fibronectin binding properties of poly(styrene) bacteriologic and tissue culture petri plates were studied. After treatment of the plastics with serum, both the rate of fibronectin binding and the maximum amount of fibronectin bound were found to be lower for bacteriologic than tissue culture plates. In contrast, when treated with purified fibronectin rather than serum, bacteriologic and tissue culture plates bound fibronectin equally well. Thus, serum proteins are more effective in inhibiting fibronectin binding to bacteriologic petri plates than to tissue culture dishes. The fibronectin binding properties of plastic substrata could be enhanced by oxidation with H2SO4 or diminished by dissolution and recasting of tissue culture dishes. Thus, the fibronectin binding properties of bacteriologic and tissue culture dishes can be interconverted. Plastics with enhanced fibronectin binding properties (tissue culture plates) were found to be hydrophilic and good substrates for cell attachment and growth while plastics with decreased fibronectin binding characteristics were found to be hydrophobic and poor substrates for cell attachment and growth. The cell-adhesive properties of bacteriologic and tissue culture plastic substrata were found to vary during incubation with cells. While cells remained firmly attached and spread on tissue culture plastics over a period of 5 days or more, previously attached cells gradually detached from bacteriologic plastics at incubation times beyond 12 h. The gradual detachment of cells from bacteriologic plates probably explains the poor properties of bacteriologic plastics for the growth of anchorage-dependent cells, in particular.     

Chromatographic investigations of macromolecules in the critical range of liquid chromatography, 10. Polymer blend analysis using a viscosity detector

Binary polymer blends were separated by liquid chromatography at the critical point of adsorption. By operating at chromatographic conditions corresponding to the critical point of one blend component, the blends were separated regardless of the molar mass distributions of the components. After the separation step both components were precisely detected by an on-line capillary viscometer. In contrast to refractive index detection, where a strong solvent peak appears in most cases, the viscosity signal is not affected by sight deviations in the mobile phase composition. Under critical conditions of adsorption of one component both blend components exhibit normal Mark-Houwink behaviour. Therefore, the viscosity detector in conjunction with a concentration detector can be used for determining the molar mass distribution of both blend components.     

Clonality and HPV infection analysis of concurrent glandular and squamous lesions and adenosquamous carcinomas of the uterine cervix

We analyzed the clonality and human papillomavirus (HPV) infection status of concurrent glandular and squamous lesions and adenosquamous carcinomas of the uterine cervix to clarify their histogenesis. The glandular and squamous components were clonally different from each other in 7 informative concurrent lesions. HPV was episomal in 2 polyclonal glandular dysplasias (GDs). HPV was in a mixed integrated-episomal form in a monoclonal GD, an adenocarcinoma in situ, and an adenocarcinoma. Both tumor components were monoclonal in origin in 6 adenosquamous carcinomas, with identical patterns of X-chromosomal inactivation and types and physical status of HPV. These results imply that the concurrent glandular and squamous lesions are formed separately, whereas adenosquamous carcinoma is more likely to be a combination tumor of monoclonal origin, and that integration of HPV has an important role in the progression from polyclonal GD through monoclonal expansion to adenocarcinoma in situ and adenocarcinoma.     

In Situ Emulsion Polymerization to Multifunctional Polymer Nanocomposites: A Review

Polymer nanocomposites are a class of composite materials containing polymer continuous phase as matrix and inorganic nanoparticles as fillers. Combining the advantages of both polymer and nanofillers, polymer nanocomposites can yield some desirable functionalities that cannot be achieved by the individual components, thus exhibiting tremendous potential for a variety of applications. However, their performances markedly depend on the dispersion and distribution of nanofillers in the polymer matrix. Recently, in situ emulsion polymerization has been demonstrated to be a powerful approach for the preparation of multifunctional polymer nanocomposites with good dispersion and homogeneous distribution of nanofillers. In this review, the fundamentals of polymer nanocomposites and their preparation strategies are briefly discussed, and then are comprehensively summarized recent advances in the design, preparation, functionalization, and applications of polymer nanocomposites via in situ emulsion polymerization. The particular focus is placed on the strategies for achieving homogeneous and good dispersion of nanofillers within polymer matrixes. Moreover, the current challenges and future opportunities of in situ emulsion polymerization to polymer nanocomposites are discussed to motivate future contributions and explore new possibilities.     

Development and characterization of a disposable plastic microarray printhead

During the last decade microarrays have become a powerful analytical tool. Commonly microarrays are produced in a non-contact manner using silicone printheads. However, silicone printheads are expensive and not able to be used as a disposable. Here, we show the development and functional characterization of 8-channel plastic microarray printheads that overcome both disadvantages of their conventional silicone counterparts. A combination of injection-molding and laser processing allows us to produce a high quantity of cheap, customizable and disposable microarray printheads. The use of plastics (e.g., polystyrene) minimizes the need for surface modifications required previously for proper printing results. Time-consuming regeneration processes, cleaning procedures and contaminations caused by residual samples are avoided. The utilization of plastic printheads for viscous liquids, such as cell suspensions or whole blood, is possible. Furthermore, functional parts within the plastic printhead (e.g., particle filters) can be included. Our printhead is compatible with commercially available TopSpot devices but provides additional economic and technical benefits as compared to conventional TopSpot printheads, while fulfilling all requirements demanded on the latter. All in all, this work describes how the field of traditional microarray spotting can be extended significantly by low cost plastic printheads.     

Reactive Compatibilization of NBR/EPDM Blends by the Combination of Mercapto and Oxazoline Groups

Summary: The reactive compatibilization of ethylene‐propylene‐diene (EPDM)/nitrile rubber (NBR) blends was performed using mercapto‐modified copolymers (mercapto‐modified EPDM, EPDMSH, and mercapto‐modified ethylene‐vinyl acetate copolymer, EVASH) in combination with oxazoline‐functionalized NBR (NBR‐ox). The best mechanical performance was achieved with the two EVASH‐based compatibilizing systems, especially the one containing the co‐reactive copolymers because of the reactivity of the oxazoline group. The presence of insoluble material in non‐vulcanized blends suggested the reactive compatibilization. The morphologies of these blends were examined through scanning electron microscopy (SEM). Blends compatibilized with the EVASH‐based systems showed finer morphologies than the non‐compatibilized blend or those compatibilized with the EPDMSH‐based systems. In non‐vulcanized NBR/EPDM (70:30 wt.‐%) blends, the presence of the co‐reactive EVASH/NBR‐ox system changes the morphology from a cocontinuous structure towards a droplet‐matrix morphology, and also results in a significant broadening of the damping curve related to the NBR transition, observed from DMTA analysis. The effect of the compatibilization on aging resistance has also been evaluated.

SEM micrograph of a non‐vulcanized NBR/EPDM blend compatibilized with a NBR‐ox/EVASH co‐reactive copolymer.     

Surface Effects on PCR Reactions in Multichip Microfluidic Platforms

We evaluated the compatibility of several common plastics, commercially available plastic tubing and disposable syringes which might be useful in the construction of microfluidic platforms with respect to the polymerase chain reaction (PCR). A simple and inexpensive plastic test module was constructed in order to evaluate some of the construction plastics. We also investigated the effect of addition of PEG 8000 to PCR reaction mixtures on the compatibility of materials. These studies identified several common plastics, plastic tubing, and disposable syringes which were compatible with the PCR reaction.