There is an ever-growing number of developments that aim to bring novel functionalities to polymer-coating systems with nanotechnology being one of them. This article will cover recent advances in the field of smart polymeric structures that are used in protective coatings in terms of stimulus and response, sensing mechanisms, and current or potential applications. Such structures are commonly based on polymers modified through organic or inorganic additives. Emphasis is placed on smart sensors used for detecting the onset of corrosion on polymer coated ferrous and nonferrous substrates. Examples of self-healing and repair through the action of microcapsules are also presented. (c) 2007 Wiley Periodicals, Inc.
Various segmented polyurethanes with a hard segment content of about 50 wt% were prepared from 4,4'-diphenylmethane diisocyanate (MDI), a poly(tetramethylene adipate) glycol with an M, of 2000, and various combinations of aliphatic diols as chain extenders by a one-shot, hand-cast bulk polymerization method. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), ultraviolet-visible spectrometry, differential scanning calorimetry (DSC), and X-ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC data indicate rather good miscibility between the soft segments and the hard segments that accounts for the good transparency. The incorporation of a small amount of a second chain extender into MDI and 1-4-butanediol-based segmented polyurethanes decreases the crystallinity of the hard segment, thus enhancing the transparency. A segmented polyurethane derived from MDI and 1,6-hexanediol exhibits better transparency due to its relatively lower crystallinity of the hard segment. (c) 2007 Wiley Periodicals, Inc.
Selecting the proper process conditions for the injection-molding process is treated as a multiobjective optimization problem, where different objectives, such as minimizing the injection pressure, volumetric shrinkage/warpage, or cycle time, present trade-off behaviors. As such, various optima may exist in the objective space. This paper presents the development of an integrated simulation-based optimization system that incorporates the design of computer experiments, Gaussian process (GP) for regression, multiobjective genetic algorithm (MOGA), and levels of adjacency to adaptively and automatically search for the Pareto-optimal solutions for different objectives. Since the GP approach can provide both the predictions and the estimations of the predictions simultaneously, a nondominated sorting procedure on the predicted variances at each iteration step is performed to intelligently select extra samples that can be used as additional training samples to improve the GP surrogate models. At the same time, user-defined adjacency constraint percentages are employed for evaluating the convergence of iteration. The illustrative applications in this paper show that the proposed optimization system can help mold designers to efficiently and effectively identify optimal process conditions. (C) 2007 Wiley Periodicals, Inc.
In this preliminary work, a new process is examined for manufacturing hollow parts from continuous fiber-reinforced thermoplastic polymer. The new process combines the basic idea of bag forming (or bladder-assisted forming) with the rotation of the mold for the processing of thermoplastic matrix composites. A pressurized membrane is used to compact the composite on the inner wall of a mold, which is placed inside a forced convection oven. The mold is removed from the oven for the cooling stage. The process was initially developed by using a thermoplastic pre-preg obtained using yarns of commingled E-glass fibers with isotactic polypropylene (iPP). A preliminary characterization of the thermoplastic composite showed that the material can be consolidated with pressures as low as 0.01 MPa, which is readily achievable with the process of this study. The design of the mold and membrane was carried out on the basis of both structural analysis of the aluminum shell and thermal analysis of the mold. The mold thickness is of great importance with respect to both the maximum pressure allowed in the process and the overall cycle time. Molding was performed on stacks of three and six layers of yarn, varying the applied pressure between 0.01 and 0.05 MPa and maximum temperature of the internal air between 185 degrees C and 215 degrees C. The composite shells obtained under different processing conditions were characterized in terms of physical and mechanical properties. Mechanical properties comparable with those obtained by compression molding and vacuum bagging were obtained. The maximum values obtained are 12.1 GPa and 290 MPa for the flexural modulus and the flexural strength, respectively. Furthermore, the results obtained show that mechanical properties improve with increasing the pressure during the cycle and with the maximum temperature used in the process. (c) 2007 Wiley Periodicals, Inc.
We have developed a one-step method for preparing nanocomposites based on powdered isotactic polypropylene (i-PP) as a matrix polymer (melt-flow index (MFI) = 7.2 g 10 min(-1)), oligo(i-PP-g-MA) (MFI = 35-70 g 10 min(-1)) as a reactive compatibilizer and docecylamine-surface-modified montmorillonite clay (organo-MMT). This method includes grafting maleic anhydride (MA) onto i-PP chains in the melt state under the controlled thermal degradation conditions and intercalative compounding of the obtained oligo(i-PP-g-MA) with i-PP and organo-MMT by reactive extrusion. The effect of extrusion parameters on MR, composition and properties of the grafted i-PPs, and mechanism of formation and properties of PP/oligo(PP-g-MA)s/organo-MMT nanocomposites were investigated by FTIR, XRD, and thermal analysis (DSC, TGA, and DTA). The results indicate that the formation of nanostructured morphologies proceeds through the formation of strong H-bonding and amidization/imidization reactions between the anhydride units of exfoliated grafted i-PP chain and alkylamine within the organo-MMT interlayers. (c) 2007 Wiley Periodicals, Inc.
We analyze an example of the application of polymer tribology to create a safety medical device, namely a retractable syringe. In service at various stages either low- or high-dynamic friction is needed. Our work focuses on a VanishPoint((R)) nonreusable safety syringe manufactured by Retractable Technologies, Inc., Little Elm, TX. Different medical-grade materials strongly affect the performance of this product. Extant tribological testing methods developed for flat surfaces are of little use. A functionality test that provides static and dynamic friction between rounded and cylindrical parts moving one inside the other gives us data not obtainable from the earlier techniques. These results combined with the liquid blowout force results (also for cylindrical surfaces) tell us that a polyolefin elastomer imparts better properties to a polypropylene-containing resin than does silica as an additive. Data-based selection of appropriate polymeric materials for components of the syringe thus becomes possible. (c) 2007 Wiley Periodicals, Inc.
Two new families of biodegradable poly[(epsilon-caprolactam)co-(epsilon-caprolactone)] and poly[(epsilon-caprolactam)-co-(delta-valerolactone)] copolymers were synthesized via anionic polymerization. The polymerization was activated with macroactivators (MAs) based on telechelic poly(epsilon-caprolactones) (PCLOs) and poly(delta-valerolactone) (PVLO) polyols. The molecular weights of the polyesters were varied to obtain a large diversity of copolymer structures and properties. The MAs were prepared by reaction of reactive hydroxyl end-groups of PCLO polyols or hydroxyl-carboxyl end-groups PVLO polyol with isophorone diisocyanate (IF). The diisocyanate-end-capped poly(lactones) were additionally blocked in sit a with epsilon-caprolactam to receive corresponding carbamoyllactam derivates. Analyses of the isolated. products by FTIR, H-1 NMR spectroscopy, and size exclusion chromatography indicated that nearly quantitative end-functionalization was achieved in all cases. The prepared MAs reduce the polymerization time to several minutes and improve the toughness of the synthesized poly(esteramides). (C) 2007 Wiley Periodicals, Inc.
A possibility of using a thermoplastic silicone elastomer (TPSE) for reduction of surface defects in the extrusion of wood-filled metallocene polypropylene (mPP) has been investigated in this work. A capillary rheometer and a single-screw extruder have been utilized to study the effect of the additive on the extrudate distortions. Maleated syndiotactic metallocene polypropylene was also used as an adhesion promoter in mPP/wood flour composites. At loadings of 50 wt% wood flour in the mPP, the extrudates come out of the die with significant tearing and surface roughness. The surface rupture mechanism is similar to that of sharkskin in neat polymers; however, the defect is much more exaggerated in the case of wood fiber-filled composites. It was found that TPSE at low concentrations (1 wt%) was able to reduce or even completely eliminate extrudate surface tearing. Increasing the extrusion speed yielded better results. Addition of a coupling agent also provides improvement in the extrudate appearance. (C) 2007 Wiley Periodicals, Inc.
Polyurethane matrix composites based on fiber-interlayered carbon fabric laminates were prepared by compression molding to assess the feasibility of this approach, when using a highly reactive resin as matrix. The polyurethane matrix was prepared using the excess isocyanate to enhance the rigidity of the system through additional crosslinking. The fiber-interlayered laminates consisted of different amount of short fibers between two carbon fabrics. Three composites containing, respectively, 12%,18%, and 26% wt/wt total carbon fibers were produced for this study. Thermal and IR spectroscopic analysis were performed to select the most suitable thermal curing conditions for the matrix. The results showed that 70 degrees C represents the minimum curing temperature required to carry out the reactions between polyol and isocyanate groups at an economical rate. In this condition, a multistep reaction occurs to consume the excess isocyanate. Mechanical strength of the composites was measured by three-point bending tests, and the data were analyzed by the Weibull statistical method. Fiber content in the interlayer is a critical parameter in the manufacture of these types of composite materials. Composites with 13% and 21% wt/wt short fibers in the interlayers (giving a total carbon fiber content of 18% and 26% wt/wt) exhibit a wider cumulative distribution of strength data due to the restrictions that they impose on the flow of the resin, thereby resulting in an inhomogeneous distribution of resin throughout the samples. A composite with 12% total carbon content (7% wt/wt short fibers) exhibits a narrower cumulative distribution, denoting a greater reliability relative to the manufacturing method used in this study. (C) 2007 Wiley Periodicals, Inc.
The possibility of improving the processing characteristics of a high-viscosity engineering polymer alloy (PPO-PA6,6) was explored through the addition of small amounts of a thermotropic liquid crystalline polymer (LCP). The thermal and rheological characteristics were examined for LCP contents up to 5 wt%. Inclusion of even a small amount of LCP (1 wt%) has resulted in a substantial decrease in the melt viscosity (similar to 50%) and in the possible lowering of the processing temperature of the PPO-PA alloy. Numerical simulation and experimental tests for the injection molding of a fairly complex component have shown that cavity filling occurs more rapidly when small amounts of LCP are added to the blend. Together with morphological examinations, these results have confirmed that LCP is thoroughly dispersed in the blend and acts as a true viscosity depressant, rather than behaving as an external lubricant. The resulting improvements in processing characteristics were also evident from the increase in the onset degradation temperature and the reduction in thermal expansion coefficient of the blends. (C) 2007 Wiley Periodicals, Inc.