Optimization of operation and changeover time for production planning and scheduling in a flexible manufacturing system

This paper deals with the production planning problem of a flexible manufacturing system. It specifically addresses issues of machine loading, tool allocation, and part type grouping with the intent of developing an operation sequencing technique capable of optimizing operation time, non-productive tool change times, and orientation change times when processing a group’s design features. A hierarchical approach has been adopted to determine the part groups – depending on the operation, tool change and orientation change times at the upper level. At the next level, we sequence the operations of the part groups. Integer programming models are formulated to group the parts and to address the operation-sequencing problem. The model is illustrated with an example related to an auto engine cylinder head machining plant.     

Dielectric investigation of the sol‐gel transition in the acrylamide/N,N′ methylenebisacrylamide system

The acrylamide/N,N′‐methylenebisacrylamide gelation process was studied by time dependent measurement of real ϵ^I and imaginary ϵ^II parts of the complex dielectric permittivity. The measurements were carried out in the frequency interval 500 Hz to 13 MHz. Strong relaxation behavior of ϵ^I and ϵ^II was observed in all dielectric spectra during the transformation from the sol to the gel state. At all frequencies a maximum in the imaginary part of dielectric constant ϵ^II was observed. The gel point was found by extrapolating this maximum to zero frequency. The behavior of ϵ^I and ϵ^II related to the gelation mechanism is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 463–466, 2000     

Synthesis of antibacterial amphiphilic elastomer based on polystyrene-block-polyisoprene-block-polystyrene via thiol-ene addition

A new type of amphiphilic antibacterial elastomer has been described. Thermoplastic elastomer, polystyrene–block-polyisoprene–block-polystyrene (PS–b-PI–b-PS) triblock copolymer was functionalized in toluene solution by free radical mercaptan addition in order to obtain an amphiphilic antibacterial elastomer. Thiol terminated PEG was grafted through the double bonds of PS–b-PI–b-PS via free radical thiol-ene coupling reaction. The antibacterial properties of the amphiphilic graft copolymers were observed. The original and the modified polymers were used to create microfibers in an electro-spinning process. Topology of the electrospun micro/nanofibers were studied by using scanning electron microscopy (SEM). The chemical structures of the amphiphilic comb type graft copolymers were elucidated by the combination of elemental analysis, ¹H NMR, ¹³C NMR, GPC and FTIR.     

Fossil fuels substitution by the solar energy utilization for the hot water production in the heating plant “Cerak” in Belgrade

The main objective of this paper is to evaluate energy and environmental benefits of the large-scale solar heating system connection with district heating system. The assessment of fossil fuels substitution by the solar energy for the hot water production for domestic use, during the summer period, is done. Hot water for district heating and domestic use is produced in heating plant “Cerak” placed in the suburb of Belgrade. The existing production and distribution system are based on fossil fuel energy, mainly on the natural gas. In the first phase of the project plan was to install about 10,000 m² of solar collectors to substitute nearly 25% of natural gas consumption. During the summer period, the saving of natural gas calculated for presented system is approximately 430,000 m³ and in this way 900 t of the CO₂ emissions would be reduced.     

Preparation and characterization of a superabsorbent slow‐release fertilizer with sodium alginate and biochar

A novel hydrogel was synthesized through the graft copolymerization of acrylic acid (AA) and acrylamide (AM) onto sodium alginate with ammonium persulfate as the initiator, methylene bisacrylamide as the crosslinking agent, and calcium chloride as the precipitating agent. Rapeseed meal biochar made at 300 °C was also used. A series of graft copolymers with various molar ratio of AA to AM was prepared. The structures of the hydrogels were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The free absorbency and rate of release were investigated. The grafting efficiency increased as the concentration of AM increased. There was a considerable percentage of nitrogen in the graft copolymers, and the release rate of nitrogen from fertilizer in soil and water decreased with increasing concentration of AM. The water retention of soil without hydrogel remained at 63 and 53.4% on the 10th and 20th days, but with the hydrogels, it was above 70% even on the last day. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45966.     

Biodegradable Poly(ε‐Caprolactone)‐Based Graft Copolymers Via Poly(Linoleic Acid): In Vitro Enzymatic Evaluation

Well‐defined graft copolymers based on poly(ε‐caprolactone) (PCL) via poly(linoleic acid) (PLina), are derived from soybean oil. Poly(linoleic acid)‐g‐poly(ε‐caprolactone) (PLina‐g‐PCL) and poly(linoleic acid)‐g‐poly(styrene)‐g‐poly(ε‐caprolactone) (PLina‐g‐PSt‐g‐PCL) were synthesized by ring‐opening polymerization of ε‐caprolactone initiated by PLina and one‐pot synthesis of graft copolymers, and by ring‐opening polymerization and free radical polymerization by using PLina, respectively. PLina‐g‐PCL, PLina‐g‐PSt‐g‐PCL3, and PLina‐g‐PSt‐g‐PCL4 copolymers containing 96.97, 75.04 and 80.34 mol% CL, respectively, have been investigated regarding their enzymatic degradation properties in the presence of Pseudomonas lipase. In terms of weight loss, after 1 month, 51.5 % of PLina‐g‐PCL, 18.8 % of PLina‐g‐PSt‐g‐PCL3, and 38.4 % of PLina‐g‐PSt‐g‐PCL4 were degraded, leaving remaining copolymers with molecular weights of 16,140, 83,220 and 70,600 Da, respectively. Introducing the PLina unit into the copolymers greatly decreased the degradation rate. The molar ratio of [CL]/[Lina] dramatically decreased, from 21.3 to 8.4, after 30 days of incubation. Moreover, reduced PCL content in PLina‐g‐PSt‐g‐PCL copolymers decreased the degradation rate, probably due to the PSt enrichment within the structure, which blocks lipase contact with PCL units. Thus, copolymerization of PCL with PLina and PSt units leads to a controllable degradation profile, which encourages the use of these polymers as promising biomaterials for tissue engineering applications.     

Cd2+, Cu2+, Pb2+, Sr2+, and Y3+ binding characteristics of 17β‐estradiol molecularly imprinted polymer particles incorporated with dicyclohexano‐18‐crown‐6 for urine bioassay

The metal ion binding characteristics of molecularly imprinted polymer (MIP) submicron particles prepared using 17β‐estradiol (E2) as a template, and incorporated with dicyclohexano‐18‐crown‐6 (DCH18C6), were studied using differential pulse anodic stripping voltammetry. When Sr²⁺ was added to DCH18C6‐E2‐MIP particles already occupied by Cd²⁺, Cu²⁺, and Pb²⁺ inside the binding sites, a displacement reaction was observed: Cd²⁺/Cu²⁺/Pb²⁺‐DCH18C6‐E2‐MIP + Sr²⁺ = Sr²⁺‐DCH18C6‐E2‐MIP + Cd²⁺/Cu²⁺/Pb²⁺. This demonstrated that DCH18C6 had stronger binding affinity for Sr²⁺ than Cd²⁺ Cu²⁺ or Pb²⁺. Strong DCH18C6 binding affinity was also observed for Y³⁺. Atomic emission spectrometry showed that DCH18C6‐E2‐MIP particles (150 mg/mL) resulted in 52% binding of Sr²⁺ (2000 ppm, at pH 6.3 ± 0.1 and ionic strength of 0.1M NaNO₂). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of diblock,triblock, and multiblock copolymers containing poly(3‐hydroxy butyrate) units

A poly[(R,S)‐3‐hydroxybutyrate] macroinitiator (PHB‐MI) was obtained through the condensation reaction of poly[(R,S)‐3‐hydroxybutyrate] (PHB) oligomers containing dihydroxyl end functionalities with 4,4′‐azobis(4‐cyanopentanoyl chloride). The PHB‐MI obtained in this way had hydroxyl groups at two end of the polymer chain and an internal azo group. The synthesis of ABA‐type PHB‐b‐PMMA block copolymers [where A is poly(methyl methacrylate) (PMMA) and B is PHB] via PHB‐MI was accomplished in two steps. First, multiblock active copolymers with azo groups (PMMA‐PHB‐MI) were prepared through the redox free‐radical polymerization of methyl methacrylate (MMA) with a PHB‐MI/Ce(IV) redox system in aqueous nitric acid at 40°C. Second, PMMA‐PHB‐MI was used in the thermal polymerization of MMA at 60°C to obtain PHB‐b‐PMMA. When styrene (S) was used instead of MMA in the second step, ABCBA‐type PMMA‐b‐PHB‐b‐PS multiblock copolymers [where C is polystyrene (PS)] were obtained. In addition, the direct thermal polymerization of the monomers (MMA or S) via PHB‐MI provided AB‐type diblocks copolymers with MMA and BCB‐type triblock copolymers with S. The macroinitiators and block copolymers were characterized with ultraviolet–visible spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, cryoscopic measurements, and thermogravimetric analysis. The increases in the intrinsic viscosity and fractional precipitation confirmed that a block copolymer had been obtained. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1789–1796, 2004     

Synthesis and comparison of crosslinked peptide nanoparticles based on diphenylalanine derivatives

Self‐assembly is a mechanism that creates novel nanomaterials with amplified properties but with stability challenges. In this report, highly stable and biocompatible anionic zwitterionic diphenylalanine nanoparticles (ZFFNPs), which are novel for the literature, are demonstrated. ZFF was crosslinked with glutaraldehyde (GA) and self‐assembled into nanoparticles in a self‐assembly mechanism like that for diphenylalaninamide nanoparticles (FFANPs). Also, ZFFNPs were compared with FFANPs in aspects of morphology, surface charge, stability, and cytotoxicity. ZFFNPs demonstrate a spherical morphology and homogenicity like FFANPs, but while ZFFNPs have negative surface groups (carboxyl), FFANPs contain polar surface groups (amide). While ZFFNPs exhibit a high stability in extremely acidic environments (pH 3–5), AFFNPs show stability in a wide pH range (pH 4–10). Both NPs are nontoxic and biocompatible. These novel anionic ZFFNPs have great promise for potential utilization in biomedical applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45930.     

Uniaxial tensile properties of TiO2 coated single wool fibers by sol‐gel method: The effect of heat treatment

Single wool fibers were coated with TiO₂ by using the sol‐gel method. The uniaxial tensile properties of TiO₂ coated single wool fibers heated at different temperatures from 25 to 200°C were investigated and compared with those of uncoated single wool fibers. It was observed that the shape of the stress–strain curve of TiO₂ coated wool fibers became the same as uncoated wool fibers and showed a similar tendency of change to uncoated wool fibers with increasing temperature. But, the TiO₂ coated wool fibers obtained higher rigidity than uncoated wool fibers and up to their rupture points; they obtained higher stress levels in three deformation regions in the stress–strain curves, which indicates stronger wool fibers. Although the breaking extension of TiO₂ coated wool fibers decreased little by about 8%, the Young's modulus of TiO₂ coated wool fibers increased significantly by 19%, which was caused mostly by an increment in the stiffness of the cuticle layer of the wool fiber, and remained relatively higher than that of uncoated wool fibers after heat treatments. Structural changes in both uncoated and TiO₂ coated single wool fibers due to thermal effect, which caused the changes in the uniaxial tensile properties and the thermal behaviors of these fibers were discussed by using spectroscopic and thermal analysis methods in detail. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 898‐907, 2013