Search

Our previous studies have confirmed the superior biocompatibility of the poly-L-lactic acid/amorphous calcium phosphate (PLLA/ACP) scaffolds (PowerScaffold) compared to PLLA scaffolds and their similar 6-month radial strength compared with TAXUS stents. In order to conduct further dynamic observations on the performance of the PowerScaffold after 12-month implantation compared with the TAXUS stents. Twenty PowerScaffold and 20 TAXUS were implanted in porcine coronary arteries. At 12-month follow-up, Quantitative Coronary Angiography showed that the stent reference vessel diameter (3.19 ± 0.25 mm vs. 2.75 ± 0.22 mm, p < 0.05), the mean lumen diameter (3.07 ± 0.22 mm vs. 2.70 ± 0.17 mm, p < 0.05) and the late lumen gain (0.45 ± 0.07 mm vs. 0.06 ± 0.06 mm, p < 0.01) were all significantly greater with the PowerScaffold than the TAXUS. As well, Intravascular Ultrasound showed the stent reference vessel area (7.74 ± 0.48 mm2 vs. 6.96 ± 0.51 mm2, p < 0.05), the mean stent area (7.49 ± 0.46 mm2 vs. 6.53 ± 0.47 mm2, p < 0.05) and the mean lumen area (7.22 ± 0.50 mm2 vs. 6.00 ± 0.48 mm2, p < 0.01) were all significantly greater with the PowerScaffold than the TAXUS. The luminal patency rate of the PowerScaffold significantly increased from 72.45 ± 6.84% at 1 month to 93.54 ± 8.15% at 12 months (p < 0.01) while the TAXUS stents were associated with a non-significant decreasing trend (89.44 ± 8.44% vs. 86.53 ± 8.22%). Pathology indicated the average thickness of the struts degraded by 14.25 ± 3.04 μm at 1 month, 23.39 ± 2.45 μm at 6 months and 35.54 ± 2.20 μm at 12 months. Immunohistochemical examination showed that the expression of inflammatory factors NF-κB gradually decreased from 1-month to 12-month (36.79 ± 4.78 vs. 5.79 ± 2.85, P < 0.01). As the late lumen gain of arteries implanted with the PowerScaffold increases over time with the growth of vessels, it effectively reverse the late vascular negative remodeling observed with the TAXUS stents, providing a better option for lumen restoration treatment in clinical practice.

Biodegradable polymers used as vascular stent coatings and stent platforms encounter a major challenge: biocompatibility in vivo, which plays an important role in in-stent restenosis (ISR). Co-formulating amorphous calcium phosphate (ACP) into poly(lactic-co-glycolic acid) (PLGA) or poly-L-lactic acid (PLLA) was investigated to address the issue. For stent coating applications, metal stents were coated with polyethylene-co-vinyl acetate/poly-n-butyl methacrylate (PEVA/PBMA), PLGA or PLGA/ACP composites, and implanted into rat aortas for one and three months. Comparing with both PEVA/PBMA and PLGA groups after one month, the results showed that stents coated with PLGA/ACP had significantly reduced restenosis (PLGA/ACP vs. PEVA/PBMA vs. PLGA: 21.24 +/- 2.59% vs. 27.54 +/- 1.19% vs. 32.12 +/- 3.93%, P < 0.05), reduced inflammation (1.25 +/- 0.35 vs. 1.77 +/- 0.38 vs. 2.30 +/- 0.21, P < 0.05) and increased speed of re-endothelialization (1.78 +/- 0.46 vs. 1.17 +/- 0.18 vs. 1.20 +/- 0.18, P < 0.05). After three months, the PLGA/ACP group still displayed lower inflammation score (1.33 +/- 0.33 vs. 2.27 +/- 0.55, P < 0.05) and higher endothelial scores (2.33 +/- 0.33 vs. 1.20 +/- 0.18, P < 0.05) as compared with the PEVA/PBMA group. Moreover, for stent platform applications, PLLA/ACP stent tube significantly reduced the inflammatory cells infiltration in the vessel walls of rabbit iliac arteries relative to their PLLA cohort (NF-kappaB-positive cells: 23.31 +/- 2.33/mm2 vs. 9.34 +/- 1.35/mm2, P < 0.05). No systemic biochemical or pathological evidence of toxicity was found in either PLGA/ACP or PLLA/ACP. The co-formulation of ACP into PLGA and PLLA resulted in improved biocompatibility without systemic toxicity.

The structure, morphology and properties of PU foams containing the novel bio-based crosslinker 3-hydroxy- N,N -bis(2-hydroxyethyl)butanamide (HBHBA) were investigated in comparison with PU foams containing the conventional crosslinker diethanolamine (DEOA). FTIR results indicate that HBHBA increases the degree of microphase separation in the foam and hydrogen bond concentration in the hard domains, suggesting that the incorporation of HBHBA produces better ordering of hard domains as compared with DEOA-crosslinked foam. Uniquely, the tri-functional crosslinker, HBHBA, can act as a chain extender due to the presence of a low reactivity secondary hydroxyl, reducing the crosslink density of the HBHBA foam vs. that of DEOA foam. Concerning foam morphology, the lower reactivity of HBHBA tends to favor larger cell sizes and more complete cell opening as compared to the more reactive DEOA. This behavior may in turn be related to the onset of phase separation and the rate of viscosity build-up. Mechanical properties measurements indicate that the elongation at break and the tensile strength of the HBHBA foam are ∼33% and 41% higher than the DEOA foam, respectively. The HBHBA foam also exhibits 40% greater tear strength and 10% greater compression strength without any loss in resilience. These results indicate that this bio-based crosslinker enhances properties and has clear potential in molded foam applications.

An hierarchical structure, composed of a ternary cocontinuous polymer blend, where carbon nanotubes are mostly localized in one of the phases through π–π interactions, is fabricated by direct melt mixing of polyamide 12 and polypropylene, as the two major components of the ternary blend, together with pyridine-modified poly(ethylene-co-methacrylic acid) as the minor component that can form strong interactions with the CNTs via π–π interactions and confined the percolated network at the polyamide/polypropylene interface. The hierarchical structure was designed by means of surface energies, and the obtained morphology was verified using electron microscopy. This ternary structure has lower electrical resistivity as compared to cocontinuous binary composites. Different polymer viscosities were used in this study in order to emphasize the importance of kinetics during cocontinuous morphology formation.

Periodontal disease is a prevalent disease that effects all types of ages. Mild cases of periodontal disease include infection and gingivitis. Severe cases of periodontal disease include loss of teeth, and the increased likelihood of systemic diseases such as: cancer, osteoporosis and pneumonia. Current treatments of periodontal disease include systemic approaches such as oral tablets of antibiotics or localized treatments such as the periodontal chip. Oral antibiotics require high dosages to effectively treat the infection therefore causing unwanted side effects. Other treatments include surgery, scaling and rooting. These methods have disadvantages as they are more invasive and require long term maintenance. The aim of this study was to develop a periodontal fiber containing Tetracycline HCl and ethylene vinyl acetate (EVA) that can be implanted in the periodontal pocket and demonstrate a drug release for up to 10 days. To develop this drug-embedded fiber, ethylene vinyl acetate and tetracycline HCL were combined and subsequently formed into a fiber. First, both materials were melted and mixed for several minutes in a Brabender mixer. The resulting material was then pelletized and the fiber was synthesized using the hot melt extrusion process. To produce the most optimal fiber, various vinyl acetate contents were mixed and extruded at high and low processing temperatures. The fiber uniformity, tensile strength, and drug release was tested on three groups: 40% vinyl acetate with low processing temperatures, 40% vinyl acetate with high processing temperatures and 7% vinyl acetate with low processing temperatures. To test the uniformity of the fiber, an inline IR reader was used to monitor the outer diameter of the fiber. Since a 0.5mm would be easily implanted into the periodontal pocket, this was the desired fiber dimension. The Instron was used to analyze the tensile strength of each group to ensure that the fiber was durable enough to withstand the harsh environment of the oral cavity. For the drug release testing the fibers were placed into H2O and incubated to 37°C. Samples from the release media were taken at various time intervals for a total of 10 days. The samples were tested on the UV spectrophotometer for peak absorbances at 360nm. The IR reader testing showed that the Elvax 40W (40% vinyl acetate content) material was easier to extrude than the Innospec (7% vinyl acetate content). The tensile strength tests of the fibers were approximately 0.025 ± 0.05 MPa. In-vitro drug release studies indicated that the low processing temperatures fibers released approximately three times the amount of tetracycline HCl than the high processing temperature group. This indicated that the fibers with low processing temperatures had the most favorable drug release profiles for bacterial inhibition. The overall feasibility for the periodontal fiber application was demonstrated in the 40% vinyl acetate group at lower processing temperatures and has shown the potential for multiple antimicrobial applications.

Different melt mixing sequences were applied to incorporate multiwalled carbon nanotubes (CNTs) into blends prepared from high density polyethylene (PE) and polyamide 12 (PA). Electron microscopy, rheology and electrical resistivity were used to characterize the morphology and microstructure. At a composition of 75PA/25PE, presence of CNT at the interface promoted by premixing the CNTs in the PE phase, resulted in finer phase morphology and a decrease in the resistivity of up to five decades relative to other mixing procedures used. At a composition of 25PA/75PE, premixing the CNT in the PA phase resulted in their segregation inside and around the PA domains and a four decade lower resistivity. Interestingly, compounds that yielded the lowest resistivity were also characterized by increased low frequency melt storage modulus ( G ′) which indicates the existence of a correlation between the two properties.

The present invention relates to the processes of preparing silkfibroin/polyethylene oxide blended materials, and the resulting materials thereof, which are suitable for biomedical applications such as wound healing. In particular, the electrospun silk fibroin/PEO mats with a silk:PEO blend ratio of 2:1 to 4:1, treated with controlled evaporation, constraint-drying techniques, and/or alcohol treatment, and/or PEO extraction, demonstrate suitable physical and biofunctional properties, such as fiber structure, topography, absorption, water vapor transmission rates, oxygen permeation, and biodegradability, relevant to biomaterial systems with utility for wound dressings.

Poly(lactic acid) (PLA) was blended with chemically modified Polyhydroxyoctanoate (mPHO) using a Haake twin-screw mixer. Due to the melt viscosity disparity between the two components, PHO was reacted with Hexamethylene diisocyanate (HDI) used as a chain extender to produce high molecular weight for improving compatibility and processability with PLA. The number average and weight average molecular weight of the PHO, reacted with 0.55 wt% HDI, were increased 314 and 275%, respectively, compared with those of the unmodified PHO. The blends were characterized for rheological, thermal, and mechanical properties. Infrared spectra confirmed the formation of the urethane linkages in mPHO. The shear viscosity, as a function of shear rate or shear stress, decreased with an increase in mPHO content, indicating that the PLA/mPHO blends show shear-thinning behavior along with the power-law model. DSC thermograms showed that the two components in the blends were found with two crystalline phases and two amorphous phases confirming the coexistence of two immiscible components. Tensile results indicated that tensile strength for blends decreased with increasing mPHO content up to 80%. A decrease in elastic modulus, as well as an increase in elongation at break, was seen as a function of mPHO content. Results of aging tests showed that the mechanical properties of the blends also dropped more at a higher PLA level when compared with those of the unaged samples.

Nanomodification of poly-hydroxy-butyrate (PHB), with hyperbranched polymers (HBP), was studied. Solid-hyperbranched polyesters of different generations were incorporated into a biobased and biodegradable, thermoplastic, polyester. Thermal, rheological, and molecular weight measurements had indicated that due to the interactions between the hydroxyl groups and the polar esters in PHB, the rate of recrystallization was significantly increased. Furthermore, the degree of crystallinity and nonisothermal crystallization temperature were also increased. Molecular weight measurements did not indicate a reduction or retention when HBPs were incorporated. These results are of great significance for the processing of biodegradable polymers and specifically for PHB, where improved processability and enhanced crystallization are of importance. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Needle-like polyanilines were prepared in aqueous media by chemical oxidation. p-Toluenesulfonic acid (pTSA) was used to protonate aniline (ANi) and readily made the anilinium complex. By slowly adding ammonium peroxydisulfate (APS) at 15°C, polyanilines were prepared in the micelles and grew to be needle-like aggregates potentially useful as conductive fillers for electromagnetic interference shielding and radar-absorbing materials. The needle-like aggregates of protonated polyaniline prepared at 15°C and 0.5 M aniline concentration with 3 h of APS addition time showed conductivity up to 3 S/cm and a maximum aspect ratio of 26 L/D. They were observed by scanning electron microscopy to peel off partially into fibrils after washing. The needle-like polyaniline-pTSA complexes prepared with 0.5 M aniline concentration showed good thermal stability up to 200°C. The high conductivity of the needle-like aggregates was ascribed to their well-developed crystalline structures, compared with those of spherical particles. J. VINYL ADDIT. TECHNOL., 13:76–86, 2007. © 2007 Society of Plastics Engineers.

Self-cleaning surfaces have received a great deal of attention, both in research studies and commercial applications. Both transparent and non-transparent self-cleaning surfaces are highly desired, as they offer many advantages and their potential applications are endless. As in many other cases, also in the case of self-cleaning surfaces, nature found a solution before man. The Lotus flower is a symbol of purity in Asian cultures, even when rising from muddy waters it stays clean and untouched by dirt, organisms and pollutants. The Lotus leaf "self-cleaning" surface is hydrophobic and rough, showing a two-layer morphology. While hydrophobicity produces a high contact angle, the two-layer morphology reduces the adhesion of dirt and water drops to the surface. Because of this low adhesion, water drops easily slide across the leaf surface carrying the dirt particles with them. In the present work the Lotus leaf morphology was mimicked using hydrophobic chemistry and a two-layer topography, with a base layer...

Young's equation describes the wetting phenomenon in terms of the contact angle between a liquid and a solid surface. However, the contact angle is not the only parameter that defines liquid–solid interactions, an additional parameter related to the adhesion between the liquid drop and the solid surface is also of importance in cases where liquid sliding is involved. It is postulated that wetting which is related to the contact angle, and interfacial adhesion, which is related to the sliding angle, are interdependent phenomena and have to be considered simultaneously. A variety of models that relate the sliding angle to the forces developed along the contact periphery between a liquid drop and a solid surface have been proposed in the literature. Here, a modified model is proposed that quantifies the drop-sliding phenomenon, based also on the interfacial adhesion that develops across the contact area of the liquid/solid interface. Consequently, an interfacial adhesion strength parameter can be defined dep...

Rationale We reported previously, in porcine coronary arteries, that the novel biodegradable PowerStent Absorb paclitaxel-eluting stent had improved and sustained structural strength and functional performance at one month post-implantation. Objective To report the stent performance at 6-month follow-up. Methods and results Six PowerStent Absorb and six TAXUS stents were randomly implanted in the left anterior descending and right coronary arteries of six Tibet miniature pigs. Quantitative coronary angiography (QCA) and intravascular ultrasound (IVUS) images were obtained at the time of implantation (T0) and at 6 months (T6). Two animals were sacrificed at T6 for histopathological evaluation. At T6, QCA showed that the mean luminal vascular diameter (mLD) between the PowerStent and the TAXUS stents were similar (2.36 ± 0.38 vs. 2.61 ± 0.31, respectively). Based on the IVUS analysis, the mLD and the mean lumen cross-sectional area (mCSA) in the PowerStent-treated arteries were similar between T0 and T6 (mLD: 2.74 ± 0.13 vs. 2.70 ± 0.20 and mCSA: 6.81 ± 0.62 mm2 vs. 6.68 ± 0.94 mm2). Histopathology showed that the PowerStent stents were well apposed to the vessel wall with no recoil, strut fracture and thrombus formation. The stents were fully covered with a layer of endothelial cells. Conclusions At six-month post-implantation, the PowerStent Absorb stents maintained their structural strength and functional performance. The development of restenosis was controlled, no stent thrombosis was observed and the stents were fully re-endothelialized. These results suggest the PowerStent Absorb stent is safe and effective for up to 6 months when implanted in porcine coronary arteries.

Organically modified montmorillonite clays were incorporated at a 5% loading level into film grade of poly-L-lactic acid (PLLA) using a variety of masterbatches based on either semi-crystalline or amorphous poly-(lactic acid), as well as biodegradable aromatic aliphatic polyester. The PLLA masterbatches and compounded formulations were prepared using a twin screw compounding extruder, while the films were prepared using a single screw cast film extruder. The thermal and mechanical properties of the films were examined in order to determine the effect of the clay and different carriers on the polymer–clay interactions. In the optimal case, when a PLLA-based masterbatch was used, the tensile modulus increased by 30%, elongation increased by 40%, and the cold crystallization temperature decreased by 15 °C, compared to neat PLLA. The properties improvement of PLLA films containing nano clays demonstrated the possibility to extend the range of biodegradable film applications, especially in the field of packaging.

The effects of nanoroughness and chemical composition on the contact and sliding angles on hydrophobic surfaces were studied theoretically and experimentally. A theoretical model based on forces developed at the contact area between a liquid drop and hydrophobic smooth or nanoroughened surface was developed and compared with the existing models, which are based on forces developed at the periphery between the drop and the solid surface. The contact area based model gives rise to an interfacial adhesion strength parameter that better describes the drop-sliding phenomenon. Consequently, relationships were derived describing the dependence between the interfacial adhesion strength of the liquid drop to the surface of a given composition, the mass of the drop, the measured contact angles and the sliding angle. For a given surface chemistry, the sliding angle on a nanometric roughened surface can be predicted based on measurements of contact angles and the sliding angle on the respective smooth surface. Variou...

The development and commercialization of nanoparticles such as nanoclays (NCs), carbon nanotubes (CNTs) and polyhedral oligomeric silsesquioxanes (POSS) offers new possibilities to tailor adhesives at the nanoscale. Four types of POSS, with reactive mono-functional groups of isocyanatopropyl, glycidoxypropyl, aminoethyl and non-reactive octaphenyl, were incorporated in concentrations of 1, 3 and 5 wt% into a polyurethane (PU)-based adhesive. Thermo-mechanical bulk properties were studied using dynamic mechanical analysis (DMA). Adhesive properties were characterized in shear and peel modes. Atomic force microscopy (AFM) was used to study the nanoscale morphology. DMA measurements indicated that the neat PU possessed a glass transition temperature (T g) of ≈ 30°C. The T g of PU/POSS-glycidoxypropyl nanocomposite adhesive increased gradually with POSS concentration to 50°C for 5 wt%. PU/POSS-octaphenyl nanocomposite adhesive exhibited an increased T g by 10°C for 5 wt%. The incorporation of POSS-isocyanatop...

A novel reverse temperature profile for the injection molding of Biopol™ was studied. It was found that both the mechanical properties and the part quality of Biopol™ were improved with this new reverse temperature process. When injection molded, most conventional thermoplastic polymers are processed at 30 to 70°C above the melting temperature; under these conditions, Biopol™ degraded rapidly and the resulting material showed poor mechanical properties. In contrast, when using a reverse temperature molding process, where Biopol™ was melted in the first zone and then was conveyed through the barrel with a decreasing temperature pathway and was injection-molded at a temperature below its melting point, the resulting material showed higher mechanical properties. The processing of Biopol™ was also greatly improved. The reverse temperature process uses the characteristically slow crystallization rate of Biopol™, which can be easily injected as hot melt even below its normal melting point. DSC analysis suggested that the reverse temperature process resulted in a more homogeneous crystalline phase than the conventional process. GPC analysis also indicated that thermal degradation of Biopol™ was largely reduced in the reverse temperature injection-molding process compared with conventional methods. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 483–491, 2004

Polyanionic rubber copolymer microparticles covered with positively charged polyaniline (PANi) as the shell were synthesized. Sodium 4‐styrenesulfonate was polymerized in a free radical initiation mechanism in the presence of a low molecular weight hydroxy‐terminated polybutadiene (HT‐PBD) matrix, which was dispersed in ethylene glycol (EG). Polymerization of aniline monomers was carried out using ammonium persulfate as the oxidant in aqueous hydrochloric acid containing polyanionic rubber copolymer microparticles. The resulting rubber‐modified PANi products form a stable and uniform aqueous latex suspension, with a PANi shell loading of 16–58% by weight. From a core‐shell microparticle latex suspension containing a PANi loading up to 37% by weight, conductive thin films with good quality can be fabricated by casting. Conductivity of these cast films, after storage for a week in a desiccator, was found to be 0.1 S/cm. These results demonstrated a promising method for the fabrication of conducting...

Polyamide 12 (PA12)/high-density polyethylene (PE)/carbon nanotubes (CNTs) composites were prepared by three melt mixing sequences; premixing the CNT in the PA phase, premixing the CNT in the PE phase, and simultaneous mixing of all components. The interfacial tension and viscosity ratio between the components were altered by modifying the PE minor phase with PE-graft-maleic anhydride (PE-g-MAH) and by using different melt flow rate PE minor phase. Scanning electron microscopy (SEM) and volume resistivity (VR) measurements show that when the matrix's viscosity is greater than that of the dispersed phase, simultaneous mixing and premixing the CNT in the PE phase form a unique microstructure that yields a VR that is 4–6 decades lower than when premixing the CNT in the PA phase. When the viscosity of the dispersed PE phase is greater, kinetic restrictions limit the migration of the CNTs from the PE phase, resulting in high VR values for all mixing procedures. The wetting parameter was used to calculate the thermodynamic drive of the CNTs localization. It was found that the MAH modification reduces the interfacial tension between the CNT and the modified PE phase, which results in selective localization of CNT in there rather than in the PA phase. This observation was confirmed in SEM imaging and also expressed in high VR values of these composites.

PCL/PEO copolymers with different compositions were obtained from ring opening polymerization of epsilon-caprolactone in the presence of ethylene oxide and characterized by various analytical techniques. Data collected from DSC and X-ray diffractometry suggested that the copolymer chains possess a blocky structure, leading to both PCL and PEO-type crystalline structures. Hydrolytic degradation of these copolymers was carried out in a pH=10.6 carbonate buffer solution at 37 degrees C. Comparison was made with a PCL homopolymer and a PCL/PEG blend which had the same gross composition as one of the copolymers. The results showed that the presence of PEO sequences considerably enhanced the hydrophilicity of the copolymers as compared with PCL homopolymer. Nevertheless, the degradability of PCL chains was not enhanced due to the phase separation between the two components. These materials should be of great interest for biomedical uses such as matrices for sustained drug delivery because of the presence of both hydrophilic and hydrophobic microdomains.

A series of blends consisting of polylactic acid (PLA) and aliphatic succinate polyester (Bionolle#3000) have been prepared. The results of the mechanical property investigation have shown that using more than 20 wt % Bionolle#3000 can significantly increase the toughness of the PLA, increase the elongation at break (more than 200%) and increase the impact strength (more than 70 J/m). These properties were not significantly affected by the aging behavior of PLA for more than two months. DMA results show that Bio#3000 reduces the elastic modulus of the blends between -15°C and 60°C.

Konjac glucomannan (KGM) exhibited liquid crystalline (LC) behaviour in aqueous solutions above 7% (w/w) concentrations as was determined by polarized optical microscopy and circular dichroism. The rheological properties of the concentrated LC solutions of KGM exhibited pseudoplastic behaviour. The fibrous extrudates retained a significant degree of flow-induced orientation as was determined by wide angle X-ray scattering, thereby indicating potential applications of KGM as fibres and films. Differential scanning calorimetry experiments showed that a significant degree of interaction occurred between KGM and water and that the KGM gels produced in our study cannot be classified as thermoreversible.

In this paper, we report on the production of modified pullulan derivatives that have been produced in solution by ring-opening e-caprolactone and [l]-lactide using a tin octanoate [Sn(Oct)2] catalyst system in DMSO. These derivatives designated as hexanoates (1 and 2) and dilactates (4−7) have been characterized and have varying degrees of substitution (DS). 1 and 2 were characterized by interesting thermal properties as well as crystalline morphology. From DSC analysis, 2, unlike the parent polysaccharide, appears to melt at 114 °C. The crystalline morphology of this polymer was characterized by X-ray powder diffraction and d spacings were calculated. This pullulan derivative possessed new crystallographic reflections not seen in either pullulan or poly (e-caprolactone). The pullulan-6 dilactate samples (4−7), produced had DS values ranging from 0.1 to 0.75. Depending upon the DS, these samples were soluble in a wide range of organic solvents including acetone and methanol. Although these materials did ...

This paper explores the copolymerization of l-lactide (l-LA) with 2,2-[2-pentene-1,5-diyl]trimethylene carbonate (cHTC). Since cHTC has a cyclohexene group, this provided a route for preparing poly(lactic acid), (PLA), based chains decorated with controlled quantities of CC substituents. Ring-opening copolymerizations of l-LA with cHTC were successfully conducted in bulk by using AlR3−H2O (R = ethyl, isobutyl), Al(OiPr)3, ZnEt2−H2O and Sn(Oct)2 as catalysts. Comparison of these copolymerizations showed that the Sn(Oct)2 catalyst system gave copolymers of relatively higher molecular weight. Increasing the reaction time of Sn(Oct)2 catalyzed copolymerizations from 6 to 24 h resulted in higher copolymer cHTC content and yield but lower copolymer molecular weight. Variation of the comonomer feed ratio was useful in regulating the content of cyclohexene pendant groups in the copolymer. However, regardless of the catalyst used, the mole percent of cHTC incorporated into the copolymer was lower than that used in...

The new cyclic carbonate monomer 2,4,8,10-tetraoxaspiro [5,5] undecane-3-one (DOXTC) was prepared in > 80% yield by the reaction of 1,3-dioxane-5,5-dimethanol with ethyl chloroformate in tetrahydrofuran (THF). DOXTC homopolymerization and copolymerizations with trimethylene carbonate (TMC) were carried out using aluminoxanes (methyl and isobutyl) as catalysts. The copolymer yields normally exceeded 90%. Carbon-13 ( 13 C) nuclear magnetic resonance ( NMR ) at 62.5 MHz resolved copolymer dyad sequences. Comparison of the fraction of dyad sequences determined by 13 C-NMR and calculated assuming a Bernoullian distribution showed that propagation statistics were approximately random for copolymerizations carried out at both 90 and 140°C. Studies by differential scanning calorimetry (DSC) showed that the DOXTC homopolymer, as well as the copolymers with high DOXTC content (F DOXTC to F TMC ≥ 7: 3), were semicrystalline. The DOXTC homopolymer had a peak melting temperature of 202°C, enthalpy of fusion of 75 J/g, and a glass transition temperature of 36°C. For copolymers with F DOXTC to F TMC ≥ 9/1, crystallization exotherms were observed both during the second heating, as well as cooling (10°C/min) DSC scans. The relationship between the copolymer glass transition and composition was in agreement with that predicted by the Fox equation. Comparison of the wide-angle X-ray scattering (WAXS) patterns of the DOXTC homopolymer with F DOXTC to F TMC of 7: 3 and 9: 1 showed that the former sample had more pronounced and better resolved crystalline reflections. These results suggest that the DOXTC homopolymer has well-ordered crystalline domains and high sample crystallinity. By increasing the molar content of 1,3-dioxane side groups in DOXTC-TMC copolymers from 0 to 50%, the water uptake by the corresponding films was increased from 5.1 to 19% (w/w).

Poly(e-caprolactone) (PCL) was reactively blended with poly(lactic acid) (PLA) using three catalysts/coupling agents in a Haake twin screw mixing chamber. Triphenyl phosphite showed the most promising results as a coupling or branching agent. PLA and PCL were also melt blended without any catalyst/coupling agents in order to make a comparison of the properties. The transesterification reaction was monitored by measuring torque values as a function of time.1H NMR was used to characterize the structure of the reactive and physical blend products. The blend samples were characterized for physical properties and biodegradation. Mechanical property measurements indicated that the elongation of the PLA/PCL blends improved significantly when compared to pure PLA especially for the reactively compatabilized blends, and that a synergism was observed for certain compositions (PLA/PCL = 80/20 or 20/80). Degradation studies showed that the enzymatic degradation rate (or normalized weight loss) of the reactively compatabilized blends were much higher than that of pure PLA and PCL, while the degradation rate of physical blends are between those of pure PLA and PCL.

Citrate esters were used as plasticizers with poly(lactic acid) (PLA). Films were extruded using a single-screw extruder with plasticizer contents of 10, 20, and 30% by weight. All of the citrate esters investigated were found to be effective in reducing the glass transition temperature and improving the elongation at break. It was observed that the plasticizing efficiency was higher for the intermediate-molecular-weight plasticizers. Hydrolytic and enzymatic degradation tests were conducted on these films. It was found that the lower-molecular-weight citrates increased the enzymatic degradation rate of PLA and the higher-molecular-weight citrates decreased the degradation rate as compared with that of unplasticized PLA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1507–1513, 1997

Poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were melt-blended and extruded into films in the PLA/PEG ratios of 100/0, 90/10, 70/30, 50/50, and 30/70. It was concluded from the differential scanning calorimetry and dynamic mechanical analysis results that PLA/PEG blends range from miscible to partially miscible, depending on the concentration. Below 50% PEG content the PEG plasticized the PLA, yielding higher elongations and lower modulus values. Above 50% PEG content the blend morphology was driven by the increasing crystallinity of PEG, resulting in an increase in modulus and a corresponding decrease in elongation at break. The tensile strength was found to decrease in a linear fashion with increasing PEG content. Results obtained from enzymatic degradation show that the weight loss for all of the blends was significantly greater than that for the pure PLA. When the PEG content was 30% or lower, weight loss was found to be primarily due to enzymatic degradation of the PLA. Above 30% PEG content, the weight loss was found to be mainly due to the dissolution of PEG. During hydrolytic degradation, for PLA/PEG blends up to 30% PEG, weight loss occurs as a combination of degradation of PLA and dissolution of PEG. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1495–1505, 1997

[l]-Lactide ([l]-LA)/ethylene oxide (EO) ring-opening copolymerizations were successfully carried out by using various catalysts including isobutylaluminoxane (IBAO), in situ AlR3·0.5H2O systems (R = ethyl, isobutyl) and Sn−Al bimetallic catalysts. Analysis of products by 1H NMR showed that methanol insoluble copolymer fractions had multiblock structures. The multiblock segment length and molecular weight of the copolymers were regulated by a variation in the reaction temperature, reaction time, reaction medium, and the catalyst structure. An increase in the reaction temperature was used to obtain shorter segment block lengths. Bulk reactions at elevated temperatures gave shorter block lengths than those of corresponding polymerizations conducted in solution (xylene). Differential scanning calorimetry (DSC) results showed two melting transitions corresponding to poly(ethylene oxide) (PEO) and [l]-polylactide ([l]-PLA) crystalline phases. The melting temperature and enthalpy of fusion for the phase-separat...

Pentene-1,5-diyl)trimethylene carbonate (cHTC) was synthesized from cyclohexene- 4,4-dimethanol in high yield (>80%). This new carbonate monomer was successfully ring-open polymerized to form P(cHTC) in bulk at 90 °C using various organometallic catalysts including aluminoxanes (methyl and isobutyl), BunSnCl4-n (n ) 1, 2, 3), BunSn(OMe)4-n (n ) 2, 3), ZnEt2, and ZnEt2-H2O. Comparison of these systems showed that the Zn- and Al-based catalysts were preferred for the preparation of high molecular weight polymers in yields g89% and reaction times of e8 h. For the BunSnX4-n catalysts investigated, values of n ) 1w hen Xi s Cl and n )2 when X is OMe resulted in relatively greater polymerization rates and higher polymer molecular weights. The effects of reaction time and monomer/ catalyst molar ratio were investigated for the Al and Zn catalysts. An outcome of this study was determining that the ZnEt2-H2O (1/0.5) catalyst for a monomer/catalyst (M/C) molar ratio of 400 and a 2 h reaction time gave a product withMn )276 000 in 98% yield. The P( c HTC) products were characterized by FTIR, 1 H-NMR, 13 C-NMR, DSC, TGA, and GPC. NMR results showed that c HTC decarboxylation did not occur during chain propagation. P( c HTC) has a moderate glass transition temperature (Tg ) 30 °C) with high thermal stability. 13 C NMR at 62.5 MHz did not resolve chain diad sequences although the polymers are likely atactic. Epoxidation of P( c HTC) vinyl side groups was carried out to various extents by using 3-chloroperoxybenzoic acid at room temperature.

The site-selective syntheses of water-soluble (O-2/O-3)-substituted amylose derivatives containing butyl ester, carboxymethyl, succinyl or quaternary ammonium side groups was carried out. In addition, routine chemical methods which did not employ protection-deprotection steps provided water soluble (O-2/O-3/O-6)-substituted products. The biodegradation of these products as a function of site-of-substitution and degrees of substitution (ds) was studied by the O-amylases from Aspergillus oryzae and Bacillus subtitis. Consistent with the results reported previously for acetyl amylose (Ref.1), the O-2/O-3 substituted butyl amylose derivatives degraded faster and to higher percentages than the corresponding O-2/O-3/O6 substituted derivatives. Also, the overall rates and percentages of degradation for butyl amylose were much lower than acetyl amylose derivatives of comparable degree and site of substitution. Therefore, for the two enzymes studied, the introduction of longer chain length acyl side groups greatly reduced substrate degradability. For the charged derivatives. the rate and percentage of degradation decreased in the order carboxymethyl > succinyl > quaternary ammonium at comparable degree and site of substitution. We concluded that, as the length of the charged side chain substituent increased the rate and extent of biodegradation decreased. Furthermore, in contrast to the results for neutral acetyl and butyl side groups, there was no significant difference in the rate and %-degradation for charged side chain substituent groups when comparing O-2/O-3 and O-2/O-3/O-6-substituted derivatives. Finally, the introduction of anionic or cationic side chain groups resulted in decreased susceptibility to α-amylase catalyzed chain cleavage when compared to similarly substituted acetyl and butyl amylose derivatives.

Nanosphere-encapsulated drugs offer a means to overcome many drug delivery limitations by localizing the site of delivery and providing controlled release. This research details the synthesis and encapsulation of ciprofloxacin in pullulan-polycaprolactone (PCL) core shell nanospheres and the characterization of these materials by 1H-NMR, UV spectroscopy, dynamic light scattering (DLS) and scanning electron microscopy (SEM).1H-NMR results confirm that the pullulan-PCL grafted copolymer was successfully synthesized. UV spectroscopy showed that the ciprofloxacin loaded nanospheres contain 35-40% ciprofloxacin by weight. DLS and SEM results indicate that the loaded nanospheres are spherical in shape and approximately 142+/-12 nm in size. Under in vitro test conditions, approximately 20% of the ciprofloxacin is released in the first 4 hours, with additional release over 10 days. The nanoparticles demonstrate bioactivity against Escheria coli and do not affect the proliferation of two human cell lines. These results demonstrate the potential of pullulan-PCL core-shell nanospheres as delivery vehicles of hydrophobic drugs, including antibiotics for localized treatments applicable to a wide-range of human bacterial infections.

The effects of physical aging, degree of crystallinity, and orientation of poly(lactic acid) (PLA) were studied using differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The samples of PLA with 96% [L] and 4% [D] contents were prepared by injection molding. The physical aging of PLA strongly depended on time and temperature. The change of rate of physical aging was very fast initially and slowed down as time increased. The enzymatic degradation of PLA was carried out with proteinase K at 37°C at a pH value of 8.6 in a Tris/HCl buffer solution. The enzymatic degradation rate was found to decrease as a function of physical aging (i.e., excess enthalpy relaxation). The rate of enzymatic degradation of PLA decreased with the increase in crystallinity. A threshold was observed when the heat of fusion was less than 20 J/g. The weight loss of PLA with a low level of crystallinity had no apparent change during any period of testing time. The rates of enzymatic degradation of stretched and injection-molded specimens were comparable.

The influences of processing variables on the mechanical properties of general grade poly-propylene prepared by oscillating packing injection molding under low pressure were reported. The density as a function of oscillating holding pressure was measured using density gradient columns. The existence of spherulites and shear-induced shish-kebab crystals was confirmed from DSC measurements. The texture of self-reinforced polypropylene was investigated using an X-ray diffractometer and an X-ray flat film camera. Investigations indicate that the mechanical properties of polypropylene can be greatly enhanced using oscillating packing injection molding. The Young's modulus and tensile strength have been enhanced from original 1.4 GPa, 31.0 MPa to 3.0 GPa, 57.8 MPa, respectively. The improvement in mechanical properties is mainly ascribed to perfect spherulites, the existence of shear-induced shish-kebab crystals, and the orientation of molecular chains. © 1996 John Wiley & Sons, Inc.

Reaction injection pultrusion (RIP) combines the injection pultrusion process with reaction injection molding (RIM) techniques to yield one of the more novel methods of thermoplastic matrix pultrusion. An experimental set-up was designed and built to pultrude nylon-6 RIM material and continuous E-glassfiber. Well-impregnated nylon-6 composites with 66.5, 68.8, 71.1, and 73.3 vol% fiber were produced. Internal temperature profile within the die was recorded during the process, and physical properties of resulting composites were measured. This paper presents results of the effect of fiber content, die temperature profile and pulling speed variations on internal temperature profile, monomer conversion, and physical properties. The study showed that increasing pulling speed lowered both peak temperature and monomer conversion. Higher die temperatures accelerated the reaction, resulting in a higher exotherm, a higher peak temperature, and a higher monomer conversion within the range investigated. Shear strength, flexual strength, flexual modulus, and transverse tensile strength were proportional to monomer conversion. Flexual modulus increased with higher fiber content within the range observed. Data allow the proper combination of die temperature profile and pulling speed to be selected to achieve a desired level of monomer conversion and physical properties. Results of this study provide basic information required for product design with nylon-6 composites as well as tool design, selection of processing conditions, and quality control for the process.

Cellulose acetate (CA) was melt compounded with two different citric acid esters: triethyl citrate and acetyl triethyl citrate. It was observed, based on the glass transition temperatures, that both plasticizers were miscible with CA. The addition of plasticizer reduced the tensile modulus and increased the elongation of CA. The biodegradation rates increased dramatically with an increase in plasticizer content.

The compost activity of poly (β-hydroxybutyrate) [P(β-HB)] and a copolymer of 20% β-hydroxyvalerate [P(β-HB-co-20% β-HV)] were studied in a simulated municipal solid waste compost test at a constant temperature of 55 °C and a constant moisture content of 54%. The goal of this study was to compare the biodegradation rate of the polymer at various time points during the composting cycle as well as to investigate the effect of the acclimation or exposure time of a sample. The test films were divided into two groups. Group one was made up of samples which were exposed to the bioreactor continuously for a total of eighteen days with the sample weight loss being measured at time increments of three days of exposure. Group two was made up of samples which were each individually only exposed to the bioreactor environment for a total of three days but the exposure was at various time points during the composting cycle. Biodegradation was measured through weight loss and normalized for thickness (μg/mm 2 ). The compost activity was found to be divided into three stages with the maximum rate of polymer degradation occurring between the tenth and fifteenth day. Higher degradation rates were observed for the continuously exposed samples. The weight loss of the P(β-HB-co-20% β-HV) was found to be significantly faster than that for the P(β-HB) in this compost test.

Poly(lactic acid) (PLA) was melt blended with poly(vinyl acetate) (PVA) using a single-screw extruder. The extruded films obtained were characterized for miscibility, physical properties, degradation and surface morphology. Differential scanning calorimetry showed that all the as-extruded films were amorphous, and that the blends were compatible as only one glass transition temperature was observed. Results obtained from physical property testing indicated that the blends exhibit synergism in the range of 5 to 30% PVA, probably due to some interactions taking place in that region. Enzymatic degradation studies showed that there was a vast difference in the weight loss of pure PLA samples and the 95/5 PLA/PVA blend. Surface tension results showed that this was due to the vast difference in the surface tension of the pure PLA films and the 95/5 blend. Deaged-free blends showed the maximum degradation, followed by aged-extruded and then deaged-fixed. Scanning electron micrographs showed that the mode of degradation differs for the aged and deaged samples. A uniform degradation pattern was seen in the case of deaged samples while the aged samples showed a non-uniform pattern of degradation.

Chitosan films were acylated under heterogeneous conditions in methanol with acetic and hexanoic anhydrides and characterized by proton nuclear magnetic resonance, elemental analysis, and multiple internal reflective Fourier transform infrared spectroscopy. The disappearance of the NH2 vibrational band at 1590 cm-1, the appearance of the amide II band at 1555 cm-1, and the relatively low intensity of the ester band at 1735 cm-1 showed that acylation at the surface was site-selective for the amino (N) functionalities. Furthermore, N-acylation at the surface region appeared complete within 1 h. The acylated chitosan films were fractionated in aqueous acetic acid for compositional analysis. Acetylation of chitosan films for 3 h gave 52% of aqueous acetic acid insoluble chitin (outer film region) and 48% unreacted chitosan. In contrast, 3 h hexanoylation reactions resulted in 99% aqueous acetic acid soluble product. Thus, film N-acetylation was more rapid than N-hexanoylation. Moreove...

Polylactide (PLA) stereocopolymers with (l) repeat unit contents of 75%, 80%, 82%, 85%, 90%, 91%, 92%, 94%, and 95% were prepared from mixtures of (l)-/(d)-lactide and (l)-/meso-lactide. Compression molding of these products gave amorphous films which, for (l) contents ≥90%, were also annealed above Tg to crystallize. Analyses by differential scanning calorimetry and wide angle X-ray scattering gave information on the crystalline order of PLA films. For identical (l) contents, stereocopolymers of (l)-/(d)-lactide had higher crystallinities than those from (l)-/meso-lactide. PLA films were incubated with proteinase K (from Tritirachium album), and the enzyme-catalyzed film weight loss rates were measured. Film crystallinity, chain stereochemical composition, and repeat unit sequence distribution were analyzed as independent variables affecting film enzymatic hydrolysis. Amorphous films from (l)/(d)-lactide copolymerizations with (l) compositions ranging from 80% to 95% exhibited film weight loss rates that...

Polymerization of racemic α-methyl-β-propiolactone (MPL) was carried out using Zn-, Sn-, La-, Y-. and Al-based organometallic catalysts. It was found that Zn(C2H5)2/H2O (1/0.6), (nC4H9)2Sn(OCH3)2, Al(OiC3H7)3, and (C2H5)2AlOC2H5 produced atactic poly(α-methyl-β-propiolactone) (PMPL), whereas (nC4H9)3SnOCH3 and Y(OiC3H7)3 formed PMPL of low isotacticity with isotactic (i) diad fractions between 0.53 and 0.56. Since the Sn-based catalysts were syndioregulating for β-methyl-β-propiolactone (BL) polymerizations, placement of the lactone methyl substituent at the α- instead of the β-position alters steric interactions between the incoming monomer and the Sn catalyst−chain end so that syndioaddition is no longer preferred. Isobutylaluminoxane (IBAO) produced a PMPL sample that can be separated by acetone into two fractions: an acetone-insoluble (AI) PMPL fraction of high isotacticity (i-diad fraction 0.85) and high molecular weight (Mn = 662 000 g/mol) and an acetone-soluble (AS) PMPL fraction of low isotactic...

The rheological behavior of biodegradable blends of starch and poly(vinyl alcohol) (PVOH) was measured as a function of temperature, shear rate, and moisture content using a capillary rheometer. An excellent correlation was found with a rheological model which was used as a means to characterize the influence of starch/PVOH content as well as a qualification of the viscosity for simulation studies. This model consisted of a power law dependence on shear rate, an Arrhenius dependence on temperature, and an exponential dependence on moisture.

Studies have been conducted to determine the time dependence of film normalized weight loss using in-laboratory simulations of a compost environment. The composting bioreactors contained a fresh synthetic waste mixture formulation which was maintained at 53°C and 60% moisture. An important result from these studies is that cellulose acetate (CA) films (approximate film thickness of between 0.025 and 0.051 mm) with degrees of substitution (DS) of 1.7 and 2.5 appeared completely disintegrated after 7 and 18 day exposure periods, respectively. Little weight loss of these films was noted under similar temperature and moisture conditions using abiotic controls. The testing protocol which was developed provided repeatable results on normalized film weight loss measurements. The dependence of the synthetic waste formulation used on polymer film weight loss was investigated using, primarily, CA DS-1.7 as a substrate. It was found that the time dependence of CA DS-1.7 film weight loss was virtually unchan...

Predominantly syndiotactic poly(β-hydroxybutyrate), syn-PHB, of variable syndioregularity (syndyad fractions 0.59, 0.62, 0.64, and 0.71) and molecular weight was prepared by the dibutyltin dimethoxide catalyzed ring opening of racemicβ-butyrolactone (BL). The crystallization behavior of the syn-PHB polymers was investigated by DSC and X-ray diffraction analyses. DSC of films after melting and annealing showed at least one, and often two distinct melting transitions occuring over a broad (often ∼ 40°C) temperature range. These results indicate that syn-PHB chain segments of variable syndioregularity form crystalline regions with very different thermodynamic stabilities. Maximum degrees of crystallinity for melt annealed 0.64- and 0.71-syn-PHB was observed at an annealing temperature (T c ) of 30°C. AtT c values at 45°C and higher, crystallization of relatively lower syndioregular chain segments was apparently excluded to variable degrees dependent onT c and sample syndiotactic dyad content. After crystallization of syn-PHB samples at elevated temperatures, ambient temperature annealing resulted in an observed lower temperature melting transition at ∼ 50°C. This result showed little to no dependence on syn-PHB syndio-regularity andT c . Both solution precipitated 0.62-syn-PHB and 0.71-syn-PHB have WAXS patterns with poorly resolved crystalline reflections superimposed on amorphous haloes indicating low levels of crystallinity (17% and 25%, respectively) and poorly formed crystals. Isothermal crystallization monitored by DSC showed that the syn- and natural origin PHB showed fastest crystallization rates at temperatures between ∼ 50°C and 70°C and 60°C and 90°C, respectively. From the dependence of the higher melting transition onT c it was determined that the equilibrium melting temperatures for 0.62-syn-PHB (M n =83,700 g/mol) and a 0.64-syn-PHB (M n =11,900 g/mol) were ∼ 157 and 154°C, respectively. An Avrami analysis of syn-PHB yielded results similar to that found for natural origin PHB indicating that crystal growth occurs by a two-dimensional mechanism.

Previous research in our laboratory reported a convenient laboratory-scale composting test method to study the weight loss of polymer films in aerobic thermophilic (53°C) reactors maintained at a 60% moisture content. The laboratory-scale compost reactors contained the following synthetic compost mixture (percentage on dry-weight basis): tree leaves (45.0), shredded paper (16.5), food (6.7), meat (5.8), cow manure (17.5), sawdust (1.9), aluminum and steel shavings (2.4), glass beads (1.3), urea (1.9), and a compost seed (1.0) which is designated Mix-1 in this work. To simplify the laboratory-scale compost weight loss test method and better understand how compost mixture compositions and environmental parameters affect the rate of plastic degradation, a systematic variation of the synthetic mixture composition as well as the moisture content was carried out. Cellulose acetate (CA) with a degree of substitution (DS) value of 1.7 and cellophane films were chosen as test polymer substrates for this work. The extent of CA DS-1.7 and cellophane weight loss as a function of the exposure time remained unchanged when the metal and glass components of the mixture were excluded in Mix-2. Further study showed that large variations in the mixture composition such as the replacement of tree leaves, food, meat, and sawdust with steam-exploded wood and alfalfa (forming Mix-C) could be made with little or no change in the time dependence of CA DS-1.7 film weight loss. In contrast, substituting tree leaves, food, meat, cow manure, and sawdust with steam-exploded wood in combination with either Rabbit Choice (Mix-D) or starch and urea (Mix-E) resulted in a significant time increase (from 7 to 12 days) for the complete disappearance of CA DS-1.7 films. Interestingly, in this work no direct correlation was observed between the C/N ratio (which ranged from 13.9 to 61.4) and the CA DS-1.7 film weight loss. Decreasing moisture contents of the compost Mix-2 from 60 and 50 and 40% resulted in dramatic changes in polymer degradation such that CA DS-1.7 showed an increase in the time period for a complete disappearance of polymer films from 6 to 16 and 30 days, respectively.

Two accelerated degradation systems are described for the marine and soil exposures of polymer films. The systems were designed to provide controlled environments in which rates of degradation could be accelerated. The goal in developing these systems was to provide a standardized basis for comparing degradation kinetics of the films. Polymer film degradation kinetics are illustrated with two bacterial polyester copolymers (8% valerate and 24% valerate in butyrate-co-valerate polyester polymers) and cellophane. Initial data on weight loss per surface area, changes in molecular weight, and changes in mechanical properties of the films are described. The long-term goals are to correlate this type of data to environmental exposure conditions and to polymer morphology and chemistry.