A review on water lubrication of polymers

Water lubrication for polymers which is an economical solution has not been completelyreviewed from the qualitative perspective. A comparative study on water lubrication of polymers helpsto understand the fundamental aspects of tribology relevant to the different applications. The use ofwater as a lubricating material has been effective after the development of phenolic resins, further towhich the advancements in thermoplastics has increased the water lubrication to a greater extent.Most of the researches on water lubrication of polymers reported a positive frictional character anduncertain wear behavior on comparing with air and oil lubrication. From the existing literature inpolymer tribology with different parameters such as contact pressure, velocity and composition ofmaterials there is a lack of knowledge in understanding the mechanism involved during the wearprocess for water lubrication. Moreover, connection between the mechanical properties of polymerunder wet condition relating to the water lubricated polymers could give appropriate results oftribological behavior. Exploring the tribo-mechanical characteristic in wet condition aids to chooseappropriate material for water lubricated applications

Effect of nanoclay orientation on oxygen barrier properties of LbL nanocomposite coated films

Layer by layer (LbL) film deposition is an efficient technique used to produce thin coatings with high gas barrier properties. In this study, multilayer composite coatings with hydrogen bonding inter-layer interactions were deposited by LbL on a PET substrate, with an alternate deposition of a nanoclay layer and different intercalating polymers layers, namely chitosan (CS), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA). The investigated coatings had two different structures, quadlayers and bilayers which are different in the number of layers in the repetitive unit (four and two respectively). The alignment of nanoclay platelets and the extent of their intercalation were studied using Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The results showed that the dispersion level and the orientation of nanoclay particles depend considerably on the molecular structure of intercalating polymers and their interactions with nanoclay. An oxygen permeability model, specific to high filler loading composites, was then developed by considering only the aspect ratio and the volume fraction of the nanoparticles

Improving PBL in Empowering Meta cognitive Skill of Students

Abstract Objective: Problem-Based Learning (PBL) is a potential constructivist learning strategy that empowers students’ Meta cognitive skill. PBL focuses on problem, involves thinking activity to solve problems, and correlates to cognitive function of students. Methods: The implementation of PBL reveals various benefits, but there are also some weaknesses in this learning strategy. Thus, it is necessary to implement a certain learning strategy that can cover the PBL weaknesses, such as Reading, Questioning, and Answering (RQA) learning strategy. RQA is a new learning strategy developed based on a fact that almost all students do not read the next lecture materials, causing failure of learning strategy planned and finally the students’ comprehension becomes low. RQA is also potential to empower students’ Meta cognitive skill. Findings: The integration of RQA and PBL learning strategy is called PBL-RQA learning strategy. This study was a quasi-experimental study designed to compare the effect of PBL, RQA, and PBL-RQA learning strategies on the students’ Meta cognitive skill of Faculty of Mathematics and Science, State University of Makassar. Application: The results of the study showed that the potency of PBL learning strategy in empowering the students’ Meta cognitive skill has been increased by integrating it to RQA learning strategy. The meta cognitive skill mean score of the students taught by PBL-RQA learning strategy was 21% higher than that of the students taught by PBL and 26.9% higher than that of the students taught by RQA learning strategy. Keywords: Answering, Meta Cognitive Skill, Problem-Based Learning, Questioning, Reading, PBL-RQ

Surface and Sub-Surface Degradation of Carbon Fiber Reinforced Composites under Reciprocating Sliding

Carbon fiber reinforced epoxy composites consist of two parts: a matrix and a reinforcement. In this thesis the reinforcement is unidirectional carbon fiber and the matrix is a thermoset polymer called epoxy. These composites are usually not applied for tribological purposes (friction, wear), although they have inherent great potential. The nature of the carbon fiber composite wear is very important, but also the risk of debonding occurring in the interface between the matrix and the reinforcement fibers. Composite manufacturers are focusing mostly on improving the mechanical properties of such materials such as fracture toughness, hardness, and strength but little attention is given to improve their tribological properties. When applying these composites in real tribological applications in either different relative humidity or immersed in water one should bear in mind their failure process. The degradation of such materials under reciprocating sliding in different environments is still not well known and the available literature still lacks a comprehensive study of the tribological behavior of such composites. It is expected that composites respond differently with changing the counter body, sliding frequency, environment, and sliding direction which complicates their degradation behavior. This work aims at investigating the tribological behavior of carbon fiber reinforced epoxy composites in ambient air and aqueous solutions under reciprocating sliding with the goal of understanding the surface and sub-surface degradation. The principal approach adopted in this work is to establish in depth our understanding of the debonding between carbon fibers and the epoxy matrix. In a first step, a stress model is developed to get a theoretical analysis of the composite response under combined compressive and shear forces. In addition, a heat model is developed to analyze the effect of surface temperature by varying either the sliding frequency or cooling the system on water immersion. Following, experimental reciprocating sliding tests are performed to validate and explain the influence of the counter body, the sliding direction to the fiber orientation, the water immersion, and the relative humidity on the composite degradation. The knowledge acquired from theoretical and experimental analyses is used to explain the failure mechanism of carbon fiber reinforced epoxy composites in sliding contacts. Thus, for the first time carbon fiber reinforced epoxy is mechanically and thermally modelled under reciprocating sliding. It is shown that modelling is a strong tool in composite tribology which is beneficial to understand the stress concentrated region and the heat mapping of the contact area. Moreover, the sub-surface investigation is for the first time characterized in-depth by cross-sectioning the wear track by focused ion beam technique which shows clearly that debonding under reciprocating sliding takes place at the fiber/matrix interface.status: publishe

Surface and sub-surface degradation of unidirectional carbon fiber reinforced epoxy composites under dry and wet reciprocating sliding

The role of water on the sub-surface degradation of unidirectional carbon fiber reinforced epoxy composite is examined. The correlation between the debonding of carbon fibers at the fiber-epoxy interface, and the wear behavior of the carbon fiber composite are discussed based on an in-depth analysis of the worn surfaces. We demonstrate that a reciprocating sliding performed along an anti-parallel direction to the fiber orientation under dry conditions results in a large degradation by debonding and breaking of the carbon fibers compared to sliding in parallel and perpendicular directions. Immersion in water has a harmful effect on the wear resistance of the carbon fiber composite. The competition between crack growth and the wear rate of epoxy matrix and/or carbon fibers in the sliding track determines the level of material loss of the composite in both test environments. © 2013 Elsevier Ltd. All rights reserved.Part of this research was done within the EU FP7-PEOPLE-2011-IRSES “Oil & Sugar”-Project (Grant Agreement No. 295202). JGB would like to thank the Executive Research Agency of the European Union for funding under the Marie Curie grant “NANODIA” (272448). This work has been partially supported by Comunidad Autónoma de Madrid (project No. S2009/PPQ-1642, AVANSENS) and Ministerio de Economía y Competitividad (FIS2012-38866-C05-05).Peer Reviewe