Friction and Adhesion of Different Structural Defects of Graphene

Graphene structural defects, namely edges, step-edges and wrinkles are susceptible to severe mechanical deformation and stresses under frictional operations. Applied forces cause deformation by folding, buckling, bending and tearing the defective sites of graphene, which lead to a remarkable decline in normal load and friction bearing capacity. In this work, we experimentally quantified the maximal normal and friction forces corresponding to the damage thresholds of the different investigated defects as well as their pull-out (adhesion) forces. Horizontal wrinkles (with respect to the basal plane, i.e. folded) sustained the highest normal load, up to 317 nN, during sliding, whereas for vertical (i.e. standing collapsed) wrinkles, step-edges and edges, the load bearing capacities are up to 113 nN, 74 nN and 63±5 nN, respectively. The related deformation mechanisms were also experimentally investigated by varying the normal load up to the initiation of the damage from the investigated defects and extended with the numerical results from Molecular Dynamics and Finite Element Method simulations

Optimization of atmospheric plasma treatment of LDPE films: Influence on adhesive properties and ageing behavior

One of the major disadvantages of low density polyethylene (LDPE) films is their poor adhesive properties. Therefore, LDPE films have been treated with atmospheric pressure air plasma in order to improve their surface properties. So as to simulate the possible conditions in an industrial process, the samples have been treated with two different sample distances (6 and 10 mm), and treatment rates between 100 and 1000 mm s-1. The different sample distances are the distance of the sample from the plasma source. The variation of the surface properties and adhesion characteristics of the films were investigated for different aging times after plasma exposure (up to 21 days) using contact angle measurement, atomic force microscopy, weight loss measurements and shear test. Results show that the treatment increases the polar component () and these changes improve adhesive properties of the material. After the twenty-first day, the ageing process causes a decrease of wettability and adhesive properties of the LDPE films (up to 60%).Fombuena Borrás, V.; García Sanoguera, D.; Sánchez Nacher, L.; Balart Gimeno, RA.; Boronat Vitoria, T. (2014). Optimization of atmospheric plasma treatment of LDPE films: Influence on adhesive properties and ageing behavior. Journal of Adhesion Science and Technology. 28(1):97-113. doi:10.1080/01694243.2013.847045S97113281Achilias, D. S., Roupakias, C., Megalokonomos, P., Lappas, A. A., & Antonakou, Ε. V. (2007). Chemical recycling of plastic wastes made from polyethylene (LDPE and HDPE) and polypropylene (PP). Journal of Hazardous Materials, 149(3), 536-542. doi:10.1016/j.jhazmat.2007.06.076Friedman, M., & Walsh, G. (2002). High performance films: Review of new materials and trends. Polymer Engineering & Science, 42(8), 1756-1788. doi:10.1002/pen.11069Wiles, D. M., & Scott, G. (2006). Polyolefins with controlled environmental degradability. Polymer Degradation and Stability, 91(7), 1581-1592. doi:10.1016/j.polymdegradstab.2005.09.010Gao, J., Lei, J., Li, Q., & Ye, S. (2004). Functionalized low-density polyethylene via a novel photografting method and its adhesion properties. Journal of Adhesion Science and Technology, 18(2), 195-203. doi:10.1163/156856104772759403Shenton, M. J., Lovell-Hoare, M. C., & Stevens, G. C. (2001). Adhesion enhancement of polymer surfaces by atmospheric plasma treatment. Journal of Physics D: Applied Physics, 34(18), 2754-2760. doi:10.1088/0022-3727/34/18/307Belgacem, M. N., Salon-Brochier, M. C., Krouit, M., & Bras, J. (2011). Recent Advances in Surface Chemical Modification of Cellulose Fibres. Journal of Adhesion Science and Technology, 25(6-7), 661-684. doi:10.1163/016942410x525867Friedrich, J., Unger, W., & Lippitz, A. (1995). Plasma modification of polymer surfaces. Macromolecular Symposia, 100(1), 111-115. doi:10.1002/masy.19951000118Ladizesky, N. H., & Ward, I. M. (1989). The adhesion behaviour of high modulus polyethylene fibres following plasma and chemical treatment. Journal of Materials Science, 24(10), 3763-3773. doi:10.1007/bf02385768Nardin, M., & Ward, I. M. (1987). Influence of surface treatment on adhesion of polyethylene fibres. Materials Science and Technology, 3(10), 814-826. doi:10.1179/mst.1987.3.10.814Villagra Di Carlo, B., Gottifredi, J. C., & Habert, A. C. (2010). Synthesis and characterization of composite membrane by deposition of acrylic acid plasma polymer onto pre-treated polyethersulfone support. Journal of Materials Science, 46(6), 1850-1856. doi:10.1007/s10853-010-5012-4Matsunaga, M., & Whitney, P. J. (2000). Surface changes brought about by corona discharge treatment of polyethylene film and the effect on subsequent microbial colonisation. Polymer Degradation and Stability, 70(3), 325-332. doi:10.1016/s0141-3910(00)00105-1Novák, I., Pollák, V., & Chodák, I. (2006). Study of Surface Properties of Polyolefins Modified by Corona Discharge Plasma. Plasma Processes and Polymers, 3(4-5), 355-364. doi:10.1002/ppap.200500163Arpagaus, C., Rossi, A., & Rudolf von Rohr, P. (2005). Short-time plasma surface modification of HDPE powder in a Plasma Downer Reactor – process, wettability improvement and ageing effects. Applied Surface Science, 252(5), 1581-1595. doi:10.1016/j.apsusc.2005.02.099Morra, M., Occhiello, E., Marola, R., Garbassi, F., Humphrey, P., & Johnson, D. (1990). On the aging of oxygen plasma-treated polydimethylsiloxane surfaces. Journal of Colloid and Interface Science, 137(1), 11-24. doi:10.1016/0021-9797(90)90038-pKim, K. S., Ryu, C. M., Park, C. S., Sur, G. S., & Park, C. E. (2003). Investigation of crystallinity effects on the surface of oxygen plasma treated low density polyethylene using X-ray photoelectron spectroscopy. Polymer, 44(20), 6287-6295. doi:10.1016/s0032-3861(03)00674-8Kim, S. H., Ha, H. J., Ko, Y. K., Yoon, S. J., Rhee, J. M., Kim, M. S., … Khang, G. (2007). Correlation of proliferation, morphology and biological responses of fibroblasts on LDPE with different surface wettability. Journal of Biomaterials Science, Polymer Edition, 18(5), 609-622. doi:10.1163/156856207780852514Borcia, G., Anderson, C. A., & Brown, N. M. D. (2004). The surface oxidation of selected polymers using an atmospheric pressure air dielectric barrier discharge. Part I. Applied Surface Science, 221(1-4), 203-214. doi:10.1016/s0169-4332(03)00879-1Pascual, M., Calvo, O., Sanchez-Nácher, L., Bonet, M. A., Garcia-Sanoguera, D., & Balart, R. (2009). Optimization of adhesive joints of low density polyethylene (LDPE) composite laminates with polyolefin foam using corona discharge plasma. Journal of Applied Polymer Science, 114(5), 2971-2977. doi:10.1002/app.30906Encinas, N., Díaz-Benito, B., Abenojar, J., & Martínez, M. A. (2010). Extreme durability of wettability changes on polyolefin surfaces by atmospheric pressure plasma torch. Surface and Coatings Technology, 205(2), 396-402. doi:10.1016/j.surfcoat.2010.06.069Takke, V., Behary, N., Perwuelz, A., & Campagne, C. (2009). Studies on the atmospheric air-plasma treatment of PET (polyethylene terephtalate) woven fabrics: Effect of process parameters and of aging. Journal of Applied Polymer Science, 114(1), 348-357. doi:10.1002/app.30618Awaja, F., Gilbert, M., Kelly, G., Fox, B., & Pigram, P. J. (2009). Adhesion of polymers. Progress in Polymer Science, 34(9), 948-968. doi:10.1016/j.progpolymsci.2009.04.007Garcia, D., Sanchez, L., Fenollar, O., Lopez, R., & Balart, R. (2008). Modification of polypropylene surface by CH4–O2 low-pressure plasma to improve wettability. Journal of Materials Science, 43(10), 3466-3473. doi:10.1007/s10853-007-2322-2Guimond, S., & Wertheimer, M. R. (2004). Surface degradation and hydrophobic recovery of polyolefins treated by air corona and nitrogen atmospheric pressure glow discharge. Journal of Applied Polymer Science, 94(3), 1291-1303. doi:10.1002/app.21134Pascual, M., Balart, R., Sánchez, L., Fenollar, O., & Calvo, O. (2008). Study of the aging process of corona discharge plasma effects on low density polyethylene film surface. Journal of Materials Science, 43(14), 4901-4909. doi:10.1007/s10853-008-2712-0Sanchis, R., Fenollar, O., García, D., Sánchez, L., & Balart, R. (2008). Improved adhesion of LDPE films to polyolefin foams for automotive industry using low-pressure plasma. International Journal of Adhesion and Adhesives, 28(8), 445-451. doi:10.1016/j.ijadhadh.2008.04.002Fresnais, J., Chapel, J. P., Benyahia, L., & Poncin-Epaillard, F. (2009). Plasma-Treated Superhydrophobic Polyethylene Surfaces: Fabrication, Wetting and Dewetting Properties. Journal of Adhesion Science and Technology, 23(3), 447-467. doi:10.1163/156856108x370127Abenojar, J., Colera, I., Martínez, M. A., & Velasco, F. (2010). Study by XPS of an Atmospheric Plasma-Torch Treated Glass: Influence on Adhesion. Journal of Adhesion Science and Technology, 24(11-12), 1841-1854. doi:10.1163/016942410x507614Lommatzsch, U., Pasedag, D., Baalmann, A., Ellinghorst, G., & Wagner, H.-E. (2007). Atmospheric Pressure Plasma Jet Treatment of Polyethylene Surfaces for Adhesion Improvement. Plasma Processes and Polymers, 4(S1), S1041-S1045. doi:10.1002/ppap.200732402Balu, B., Berry, A. D., Patel, K. T., Breedveld, V., & Hess, D. W. (2011). Directional Mobility and Adhesion of Water Drops on Patterned Superhydrophobic Surfaces. Journal of Adhesion Science and Technology, 25(6-7), 627-642. doi:10.1163/016942410x525849Bhattacharya, S., Singh, R. K., Mandal, S., Ghosh, A., Bok, S., Korampally, V., … Gangopadhyay, S. (2010). Plasma Modification of Polymer Surfaces and Their Utility in Building Biomedical Microdevices. Journal of Adhesion Science and Technology, 24(15-16), 2707-2739. doi:10.1163/016942410x511105Das, S., Neogi, S., Chainy, G. B. N., & Guha, S. K. (2011). A Novel Two-Step Procedure for Plasma Surface Modification of Low-Density Polyethylene for Improved Drug Adhesion in Intra Uterine Devices (IUDs). Journal of Adhesion Science and Technology, 25(1-3), 151-167. doi:10.1163/016942410x503285Schulz, U., Munzert, P., & Kaiser, N. (2010). Plasma Surface Modification of PMMA for Optical Applications. Journal of Adhesion Science and Technology, 24(7), 1283-1289. doi:10.1163/016942409x12561252292026Silverstein, M. S., Breuer, O., & Dodiuk, H. (1994). Surface modification of UHMWPE fibers. Journal of Applied Polymer Science, 52(12), 1785-1795. doi:10.1002/app.1994.070521213Inagaki, N., Narushim, K., Tuchida, N., & Miyazaki, K. (2004). Surface characterization of plasma-modified poly(ethylene terephthalate) film surfaces. Journal of Polymer Science Part B: Polymer Physics, 42(20), 3727-3740. doi:10.1002/polb.20234Nakamatsu, J., Delgado-Aparicio, L. F., Da Silva, R., & Soberon, F. (1999). Ageing of plasma-treated poly(tetrafluoroethylene) surfaces. Journal of Adhesion Science and Technology, 13(7), 753-761. doi:10.1163/156856199x00983Yun, Y. I., Kim, K. S., Uhm, S.-J., Khatua, B. B., Cho, K., Kim, J. K., & Park, C. E. (2004). Aging behavior of oxygen plasma-treated polypropylene with different crystallinities. Journal of Adhesion Science and Technology, 18(11), 1279-1291. doi:10.1163/1568561041588200Morent, R., De Geyter, N., Leys, C., Gengembre, L., & Payen, E. (2007). Study of the ageing behaviour of polymer films treated with a dielectric barrier discharge in air, helium and argon at medium pressure. Surface and Coatings Technology, 201(18), 7847-7854. doi:10.1016/j.surfcoat.2007.03.018Zhao, B., & Kwon, H. J. (2011). Adhesion of Polymers in Paper Products from the Macroscopic to Molecular Level — An Overview. Journal of Adhesion Science and Technology, 25(6-7), 557-579. doi:10.1163/016942410x52582

Advances in modeling transport phenomena in material-extrusion additivemanufacturing: Coupling momentum, heat, and mass transfer

Material-extrusion (MatEx) additive manufacturing involves layer-by-layer assembly ofextruded material onto a printer bed and has found applications in rapid prototyping.Both material and machining limitations lead to poor mechanical properties of printedparts. Such problems may be addressed via an improved understanding of thecomplex transport processes and multiphysics associated with the MatEx process.Thereby, this review paper describes the current (last 5 years) state of the art modelingapproaches based on momentum, heat and mass transfer that are employed in aneffort to achieve this understanding. We describe how specific details regardingpolymer chain orientation, viscoelastic behavior and crystallization are often neglectedand demonstrate that there is a key need to couple the transport phenomena. Such acombined modeling approach can expand MatEx applicability to broader applicationspace, thus we present prospective avenues to provide more comprehensive modelingand therefore new insights into enhancing MatEx performanc

The prediction of clay contents in oil shale using DRIFTS and TGA data facilitated by multivariate calibration

The prediction of clay content in oil shale is important for the optimisation of oil shale processing conditions and process feasibility. The multivariate calibration technique of partial least squares regression (PLSR) was implemented in order to predict clay content in oil shale samples taken from the Stuart oil shale deposit, Queensland, Australia. The calibration data used were the diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) spectra of 34 oil shale samples. DRIFTS data from another set of 20 oil shale samples were used for model validation. The data pre-processing includes the use of derivatives facilitated by the Savitsky-Golay nine-points' method. A four components model was constructed and it showed a root mean square error of calibration (RMSEC) of 4.79% and a root mean square error of prediction (RMSEP) of 4.35%. TGA data sets were also used to construct a calibration model, which produced less accurate results than DRIFTS. DRIFTS, when combined with multivariate calibration, provided an accurate in situ method of evaluating clay content in oil shale. Clay content measured using XRD was used as a reference

Injection stretch blow moulding process of reactive extruded recycled PET and virgin PET blends

Reactive extruded recycled PET (RER-PET) was blended with virgin PET in order to find optimum composition for producing bottles using injection stretch blow moulding (ISBM) process. Two variables were investigated namely, RER-PET concentration in the blend with virgin PET and RER-PET intrinsic viscosity, [eta]. The variability of [eta] was facilitated by changing PMDA chain extender concentration in the production of RER-PET. Different molecular, mechanical, barrier and optical tests such as infrared, burst pressure, top load strength, drop impact, environmental stress cracking, liquid permeation, gas permeation, and clarity were conducted. The aim was to evaluate the properties of the bottles in response to different blends compositions. Bottles made from RER-PET and virgin PET blends showed similar and better mechanical and barrier properties at certain compositions to those made from Virgin PET. The effects of RER-PET molecular properties such as intrinsic viscosity, chain orientation and conformation on bottles mechanical, barrier and optical properties are detailed

Recycled poly(ethylene terephthalate) chain extension by a reactive extrusion process

A commercial-scale reactive extrusion processing system for recycled poly(ethylene terephthalate) (PET) flakes with an added chain extender, pyromellitic dianhydride (PMDA), was investigated. The PMDA concentration was varied with the intention of reaching a higher recycled PET intrinsic viscosity ([eta]). The effect of changing the extruder residence time on the system's stability and the recycled PET [eta] was also investigated. Reactive extruded PET with a PMDA concentration up to 0.3 wt% was found to have a higher [eta] and lower carboxyl content than recycled PET processed in a normal extrusion system. A shift in [eta] of about 0.18 dl/g was obtained with a 0.3 wt% PMDA concentration. A PMDA concentration above 0.3 wt% produced chemical. thermal and hydrodynamic instability in the system, causing crosslinking reactions and gel formation. The reactive extrusion system was stable at low residence time (45 s) and moderate (0.15 wt%) PMDA concentration; however, using 0.2 wt% PMDA produced higher reactive extruded recycled PET [eta] with lower carboxyl content than other PMDA concentration levels examined. Residence times higher than 45 s produced higher reactive extruded recycled PET [eta]. Reactive extruded recycled PET was also tested for mechanical properties

The effect of chain extension on the thermal behaviour and crystallinity of reactive extruded recycled PET

Recycled poly(ethylene terephthalate) (R-PET) was chain extended with pyromellitic dianhydride (PMDA) in a commercial size twin-screw reactive extrusion system. Temperature-modulated differential scanning calorimetry (TMDSC) was used to evaluate the effect of the chain extension process on the thermal transitions and crystallinity of R-PET. Reactive extruded recycled PET (RER-PET) samples were tested based on different PMDA concentration and reactive extrusion residence times. The glass transition temperature (T-g) did not show a significant change as a function of PMDA addition or the extrusion residence time. Melting temperature (T-m) and crystallisation temperature (T-c) decreased with increasing PMDA concentration and with increasing extrusion residence time. RER-PET samples showed double melting peaks, it is believed that different melting mechanism is the reason behind this phenomenon. The crystallinity of RER-PET samples is lower than that of R-PET. RER-PET samples at constant PMDA concentration showed a decrease in crystallinity with increasing extrusion residence time. Results suggest that the reactive extrusion process is more dependent on PMDA concentration rather than reactive extrusion process residence time