Effect of the network structure on thermal and mechanical properties of mesogenic epoxy resin cured with aromatic amine

The epoxy resin containing a typical mesogenic group such as biphenol was cured with catechol novolak and aromatic diamines which have neighboring active hydrogens. In the biphenol-type epoxy resin cured with catechol novolak, 4,4′ diaminodiphenylmethane, and p-phenylenediamine (PPD), the glass-rubber transition almost disappeared, and thus a very high elastic modulus was obtained in the high temperature region. It is clear that the thermal motion of the network chains is significantly suppressed in these cured systems. In addition, in the PPD-cured system, a characteristic pattern like a schlieren texture was clearly observed under the crossed polarized optical microscope. Thus we conclude that the mesogenic group contained in the epoxy molecule is oriented in the networks when the mesogenic epoxy resin is cured with phenols and diamines which have neighboring active hydrogens. On the other hand, the biphenol-type resin cured with 3,3′,5,5′-tetraethyl-4,4′-diamino diphenylmethane (TEDDM) showed a well-defined glass-rubber transition and, thus, a low rubbery modulus. In this cured system, no characteristic pattern was observed under the crossed polarized light. These results show that the large branches, such as ethyl groups on the network chains, prevent the orientation of network chains which contain the mesogenic group. © 1997 John Wiley & Sons, Inc.     

A hybrid algorithm for the Heterogeneous Fleet Vehicle Routing Problem

This paper deals with the Heterogeneous Fleet Vehicle Routing Problem (HFVRP). The HFVRP generalizes the classical Capacitated Vehicle Routing Problem by considering the existence of different vehicle types, with distinct capacities and costs. The objective is to determine the best fleet composition as well as the set of routes that minimize the total costs. The proposed hybrid algorithm is composed by an Iterated Local Search (ILS) based heuristic and a Set Partitioning (SP) formulation. The SP model is solved by means of a Mixed Integer Programming solver that interactively calls the ILS heuristic during its execution. The developed algorithm was tested in benchmark instances with up to 360 customers. The results obtained are quite competitive with those found in the literature and new improved solutions are reported.     

Anterior cruciate ligament graft impingement against the posterior cruciate ligament: diagnosis using MRI plus three-dimensional reconstruction software

OBJECTIVE: The purpose of this study was to evaluate anterior cruciate ligament (ACL) impingement against the posterior cruciate ligament (PCL) with the knee in an extended position, which arthroscopy cannot detect. MATERIALS AND METHODS: Ten normal knees and 30 ACL-reconstructed knees were assessed using MR imaging. The three-dimensional reconstruction of the ACL, PCL, femur and tibia were carried out using commercially available three-dimensional reconstruction software. Anterior cruciate ligament impingement against the PCL was graded into three categories: Grade 1, some space between the ligaments; Grade 2, no space between the ligaments, and the reconstructed ACL ran straight; and Grade 3, the reconstructed ACL did not run straight. The angle of the reconstructed ACL against the tibial plateau was also measured. RESULTS: All normal knees were classified as Grade 1. The 30 reconstructed knees were classified as follows: Grade 1, 12 cases; Grade 2, 7 cases; and Grade 3, 11 cases. The mean angle of the Grade 3 reconstructed ACL knees was significantly more vertical against the tibia as compared with the Grade 1 knees (P<.05). The postoperative KT-2000 side-to-side difference of the Grade 3 knees (2.8+/-4.5 mm) was larger than that of the Grade 1 knees (0.2+/-1.7 mm) and Grade 2 knees (-0.6+/-2.2 mm), but no statistically significant difference could be detected between the three groups in the postoperative KT-2000 data. CONCLUSION: This method is useful to evaluate ACL impingement against PCL, which cannot be detected by conventional arthroscopy during the operation. The surgeon should pay careful attention to the coronal angle of the reconstructed ACL.     

Novel urethane/epoxy resin hybrid materials using a moisture‐curing system

Novel curing systems of a urethane/epoxy resin [diglycidyl ether of bisphenol A (DGEBA)] alloy using the moisture‐latent hardener ketimine (K‐systems) were investigated on the DGEBA‐rich side and were compared with aromatic diamine curing systems (A‐systems). Almost all the added DGEBA was separated from the polyurethane matrix and dispersed as 2–10‐μm‐diameter particles after curing in the A‐systems. Therefore, DGEBA did not act as a reinforcing agent for the polyurethane matrix. However, 50% of the added DGEBA was dispersed as particles with a diameter of 1–4 μm, and the other 50% was incorporated into the polyurethane matrix in the novel K‐systems. Therefore, the polyurethane matrix in the K‐systems should be reinforced effectively by both incorporated and finely dispersed DGEBA and should result in significant improvements in the stress–strain properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1137–1144, 2004     

Relationship between fracture toughness and domain size of liquid‐crystalline epoxy resins having polydomain structure

A liquid‐crystalline (LC) epoxy resin was cured at different temperatures and some types of curing systems having different phase structures (isotropic or polydomain, which have a microscopically ordered LC network structure) were obtained. The diameters of each domain in the polydomain system changed from the small to the larger size. The diameters of the LC domains were evaluated using a polarized optical microscope and the polarized microscopy FTIR mapping method. These systems were used to investigate the relationship between the network arrangement and mechanical properties. The fracture toughness of the cured systems was related to the enlargement of the ordered area in the network structures. With the toughness improvement, the meandering cracks were observed at the fracture surfaces. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 156–165, 2009     

Thermomechanical properties of liquid‐crystalline epoxy networks arranged by a magnetic field

During the curing process of a liquid‐crystalline epoxy resin, a relatively strong magnetic field was applied, and the thermomechanical properties of the cured resin were investigated. The network orientation and mechanical properties of the cured system were evaluated with wide‐angle X‐ray diffraction, dynamic mechanical analysis, and fracture toughness testing. The cured system was found to have an anisotropic network structure, which arranged along the applied field, and the anisotropy was reflected in the thermomechanical properties. In particular, the fracture toughness of the system dramatically increased when the network chains were arranged across the direction of the crack propagation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 758–765, 2004     

Branch-and-cut with lazy separation for the vehicle routing problem with simultaneous pickup and delivery

We propose a branch-and-cut algorithm for the VRPSPD where the constraints that ensure that the capacities are not exceeded in the middle of a route are applied in a lazy fashion. The algorithm was tested in 87 instances with 50–200 customers, finding improved lower bounds and several new optimal solutions.     

Rigid molecular architectures that comprise a 1,3,5-trisubstituted benzene core and three oligoaryleneethynylene arms: light-emitting characteristics and pi conjugation between the arms

In view of increasing interest in light-emitting materials, we have investigated the light-emitting characteristics and occurrence of conjugation between arms of star-shaped rigid molecules that comprise a 1,3,5-triethynylbenzene core and methoxy group-substituted oligo(p-phenylethynylene) arms. Consequently, we achieved the ultimate goal (Phif approximately 1.0, log epsilon > 5) for organic molecules with respect to light-emitting ability by creating very intense violet-blue (8, Phif = 0.97, log epsilon = 5.11) and blue (9, Phif = 0.98, log epsilon = 5.29) bright light-emitters. Also, pi conjugation was found to occur between the arms of 9 despite the meta-substituted system. We found a linear relationship of kr (with positive slope) and kd (with negative slope) with the number of dimethoxyphenyleneethynylene units for MMPT (4, 6, 8) and DMPT (5, 7, 9) homologues and the contrasting solvent effect on lambdaem of 8 and 9. It is also interesting that lambdaabs, epsilon, lambdaem, and Phif of 9 are greater than those of the corresponding banana- and rod-shaped molecules.