High-density Polyethylene Sheets Research Articles

Simulation and design of a fast neutron radiography detector based on MCP

A fast neutron detector, consisting of a high-density polyethylene sheet, a micro-channel plate, a phosphor screen, a reflection mirror and a CCD camera, is proposed for fast neutron radiography purpose. To optimize the design of the detector, a series of simulations are performed by using Geant4 code. Simulation results indicate that the maximum conversion efficiency of the high-density polyethylene is about 0.38% when its thickness is 2 mm. To ensure the spatial resolution of the detector, the distance between high-density polyethylene and micro-channel plate should be as small as possible. The gap between MCP and PS is selected as 2 mm with a bias voltage of −4 kV to balance the luminescence efficiency and the spatial resolution of the PS. With the optimized structure, the detection efficiency of the detector is calculated to be 0.14% and the spatial resolution is possibly better than 500 μm.

Large strain, high rate semi‐solid deformation of high density polyethylene at elevated temperatures

High density polyethylene (HDPE) is predominately processed from the molten state. However, there is the potential to enhance the mechanical properties by forming below the melt temperature, in the semi‐solid phase. To further investigate this enhancement, HDPE sheets were deformed under constant width, simultaneous equal‐biaxial (EB), and sequential biaxial deformation. The samples were deformed at strain‐rates, from 4 to 16 s−1, up to nominal strains of 3.0 at temperatures below 130°C. The strain‐rate and high‐strain level applied were chosen so that the data was comparable to the thermoforming process. It was discovered that in order for the HDPE sheet to deform at the high‐rate and high strains the processing temperature must be between 126°C and 130°C. This resulted in a processing window that was particularly small, 5°C, and that within this window a temperature change of 1°C had a significant impact on the stress–strain response. The samples were analyzed post deformation, where the elastic modulus was found to increase by a factor of 2.08 in the machine direction, when deformed via EB at 129°C. The results showed that HDPE can be deformed to strain levels comparable to the thermoforming process. POLYM. ENG. SCI., 58:1516–1522, 2018. © 2017 Society of Plastics Engineers

Influences of friction stir welding parameters on morphology and tensile strength of high density polyethylene lap joints produced by double-pin tool

A double-pin tool is adopted in the submerged friction stir lap welding of high density polyethylene sheets in the present investigation. Effects of welding parameters (rotational speed, welding speed, plunge depth) on weld morphology and tensile strength are investigated. The experiment is arranged by taguchi’s L9 orthogonal array. Macromorphology and microstructure of three typical welds are observed and compared. Analysis of variance is adopted to assess the importance of each welding parameter to the joint strength. The results show that joint with low tensile strength presents poor weld formation. Voids and cracks can be observed in the nugget by scanning electron microscope. Joint with high strength shows excellent nugget formation and inverted bowl-shaped weld cross section. Joint strength increases with the increase of rotational speed or the decrease of welding speed. Small or large plunge depth is not beneficial to the joint strength. The joint with maximum tensile strength of 15.3MPa is obtained at rotational speed of 1300 r/min, welding speed of 20mm/min and plunge depth of 0.1mm. Welding speed has the most significant effect on the joint strength, about 75.37%, while plunge depth has the least influence.

On the friction stir welding, tool design optimization, and strain rate-dependent mechanical properties of HDPE–ceramic composite joints

Friction stir welding is a recently developed technique for joining low-melting metals and polymers. In the present work, friction stir welded joints of high-density polyethylene (HDPE) sheets were produced using a newly designed tool with a concave shoulder and a grooved conical pin. The joints were produced with and without the additions of ceramic particulates including silicon carbide (SiC), alumina, graphite, and silica. The effect of strain rate on the tensile properties of base material and plain welded joints was examined. In addition to tensile properties of composite joints, hardness profiles across the weld nugget were analyzed. It was observed that the increasing strain rate improved both the tensile strength and the ductility of the plain welded joints. The tool was able to yield a joint efficiency of around 84% in the plain welded samples. Although, in terms of joint efficiency, the composite joints were less efficient than the plain welded HDPE, SiC additions were found to yield better material properties relative to other reinforcements. Finally, it was concluded that an SiC–HDPE composite joint can be of practical importance in high strain rate applications, provided the optimum tool design and stir welding parameters are available.

Biodegradation of Polyethylene by Green Photosynthetic Microalgae

Conventional methods of polyethylene degradation including incineration, landfill and chemical treatment are lethal to the neighboring environment by causing hazardous effects on living organisms. A better solution for the complete degradation of polyethylene has not yet been formulated. However, to solve this global issue biological mode of polyethylene degradation may be evaluated and developed in the upcoming future. In this research investigation, microalgae like green algae, blue-green algae and diatoms were isolated from the domestic polyethylene bags dumped in the suburban water bodies and studied for its potency on deterioration of polyethylene. The dumped waste polyethylene bags were collected from three different sites of (Maduravoyal, Vanagaram and Poonamallee) Chennai, Tamil Nadu, India. Colonized mat of microalgae were isolated from the polyethylene sheets and the most dominant three different groups of microalgae were selected for the biological treatment of LD (low density) and HD (high density) polyethylene sheets. The most dominant microalgae were Scenedesmus dimorphus (Green microalga), Anabaena spiroides (blue-green alga) and Navicula pupula (Diatom). The T. S. (Transverse section) of polyethylene sheet has shown the proliferation of microalgae in both outer and inner sides of the polyethylene sheet and the erosion cum degradation can be seen obviously. The biological treatment of the selected microalgae on the LD and HD polyethylene sheets with their respective culture media resulted that the microalgae proliferated more on the LD than the HD polyethylene sheets followed by the highest percentage of degradation was obtained from Anabaena spiroides treatment (8.18%). Similarly, among the three microalgal groups treated over the LD polyethylene sheets. The scanning electron microscopical study reveals that the degradation was obviously evident in the treatment of LD polyethylene sheets using the microalga Anabaena spiroides (filamentous blue-green alga) and was found to grow feasibly rather than the other microalgae.

Experimental characterization of heat transfer in an additively manufactured polymer heat exchanger

In addition to their low cost and weight, polymer heat exchangers offer good anticorrosion and antifouling properties. In this work, a cost effective air-water polymer heat exchanger made of thin polymer sheets using layer-by-layer line welding with a laser through an additive manufacturing process was fabricated and experimentally tested. The flow channels were made of 150μm-thick high density polyethylene sheets, which were 15.5cm wide and 29cm long. The experimental results show that the overall heat transfer coefficient of 35–120W/m2K is achievable for an air-water fluid combination for air-side flow rate of 3–24L/s and water-side flow rate of 12.5mL/s. In addition, by fabricating a very thin wall heat exchanger (150μm), the wall thermal resistance, which usually becomes the limiting factor on polymer heat exchangers, was calculated to account for only 3% of the total thermal resistance. A comparison of the air-side heat transfer coefficient of the present polymer heat exchanger with some of the commercially available plain plate fin heat exchanger surfaces suggests that its performance in general is superior to that of common plain plate fin surfaces.

Synthesis of high dispersible hydrophilic poly(ethylene glycol)/vinyl silane grafted silica nanoparticles to fabricate protein repellent polyethylene nanocomposite

Fabrication of protein repellent polymeric surface is a challenging issue for researchers in manufacturing biocompatible composites and low fouling membranes. In this study, poly(ethylene glycol) (PEG) and vinyl silane functional groups grafted silica nanoparticles (NPs) were synthesized by using one-pot/one-step sol-gel method. The fabricated NPs were dispersed in the high density polyethylene (HDPE) matrix to analyze the protein repellent property of HDPE sheets. FTIR results confirmed the successful grafting of both PEG and vinyl moieties on the silica NPs. TEM and DLS analyses showed that in the presence of both PEG and vinyl functional groups, the particles’ sizes were reduced to about 10nm. Dispersion of NPs in HDPE was obtained through blending in the presence of an initiator followed by the characterizations. The results obtained from backscatter electrons (BSE) images of HDPE nanocomposites revealed that PEG grafted silica NPs agglomerated in the HDPE matrix due to the lack of interaction between NPs and polymer molecular chains. However, dispersion of modified silica NPs was greatly improved in presence of vinyltrimethoxysilane (PEG/vinyl grafted silica NPs) due to the good compatibility between vinyl functional group of NPs and HDPE molecular chains. The contact angle of pure HDPE flat sheet sample was also reduced from 127 to 64 degree by adding 4% of PEG/vinyl grafted silica NPs due to the inherent hydrophilic characteristic of PEG. Static protein adsorption test showed that presence of vinyl moieties in the PEG modified NPs, significantly improved the percent reduction in protein adsorption, e.g. in case of 4wt% PEG/vinyl grafted silica NPs, it decreased from 0.0230 to 0.0012mg/(mlmm2) (>94%).

Effect of annealing temperature on pore formation in preparation of advanced polyethylene battery separator membranes

Polymeric separator membranes are a key component in modern lithium ion batteries, as they are placed between anode and cathode to prevent short-circuiting while at the same time allowing an efficient diffusion of Li ions. Manufacturing conditions must be finely tuned to reach the many diverse and conflicting requirements for battery separators used in modern consumer applications as well as in electric vehicles. Little has been published about these proprietary combined extrusion/biaxial stretching processes. This work presents a closer look on one of the key aspects of separator membrane formation. Extruded sheets of high density polyethylene containing a hydrocarbon solvent as plasticizer were stretched in machine direction and annealed at temperatures between 100°C and 120°C, i.e., in a range between the onset of melting and actual melting temperature, as deduced from differential scanning calorimetry. The formation of stacked-lamellar morphologies as seen in scanning electron microscopy required a minimum strain and was also influenced by processing temperatures. The increase of the annealing temperature led to a significant increase in crystallinity and chain orientation as revealed by texture analysis, performed using X-ray powder diffraction studies on samples after dedicated preparation. After a second stretching step in transversal direction, a clear correlation to separator membrane permeability and porosity was found, with a higher crystallinity leading to lower Gurley values, i.e. higher permeabilities. The effects of blending high density with ultra-high molecular weight polyethylene of different molecular weight onto structure and morphology were also elucidated in detail. In light of the growing market of electric vehicles, high performance and safety are the main focus during separator production. The influence of important production parameters on final membrane properties is discussed.

Microstructure and tensile properties of dissimilar submerged friction stir welds between HDPE and ABS sheets

In this paper, dissimilar lap joints of high-density polyethylene (HDPE) and acrylonitrile butadiene styrene (ABS) sheets were obtained by submerged friction stir welding. The multiwalled carbon nanotubes (MWCNTs) were introduced into the HDPE/ABS joint in order to improve the tensile properties of the joints. The effects of different rotational rates, plunge depths, and traverse speeds on the microstructure and tensile strength of joints were investigated. Microstructural evolution of joints fabricated at different process parameters had been observed using a field emission scanning electron microscope (FESEM). Some defects such as pores and cracks were found at inappropriate processing parameters. The tensile test was carried out as the mechanical properties of joints. The maximal tensile strength was 14.7 MPa, which reached more than 65.3 % of the parent HDPE strength.

Effect of wall suction on rotating disk absolute instability

This research investigates the effect of uniform suction on the absolute instability of Type I cross-flow modes in the boundary layer on a rotating disk. Specifically, it is designed to investigate whether wall suction would transform the absolute instability into a global mode, as first postulated in the numerical simulations of Davies & Carpenter (J. Fluid Mech., vol. 486, 2003, pp. 287–329). The disk is designed so that with a suction parameter of $0.2$, the radial location of the absolute instability critical Reynolds number, $Re_{c_{A}}=650$, occurs on the disk. Wall suction is applied from $Re=317$ to 696.5. The design for wall suction follows that of Gregory & Walker (J. Fluid Mech., 1960, pp. 225–234) where an array of holes through the disk communicate between the measurement side of the disk and the underside of the disk which is inside of an enclosure that is maintained at a slight vacuum. The enclosure pressure is adjustable so that a range of suction or blowing parameters can be investigated. The holes in the measurement surface are covered by a compressed wire porous mesh to aid in uniformizing the suction on the measurement surface of the disk. The mesh is covered by a thin porous high-density polyethylene sheet featuring a $20~{\rm\mu}\text{m}$ pore size which provides a smooth finely porous surface. A companion numerical simulation is performed to investigate the effect that the size and vacuum pressure of the underside enclosure have on the uniformity of the measurement surface suction. Temporal disturbances are introduced using the method of Othman & Corke (J. Fluid Mech., 2006, pp. 63–94). The results document the evolution of disturbance wavepackets in space and time. These show a temporal growth of the wavepackets as the location of the absolute instability is approached which is in strong contrast to the temporal evolution without suction observed by Othman and Corke. The results appear to support the effect of wall suction on the absolute instability postulated by Thomas (PhD thesis, 2007, Cardiff University, UK) and Thomas & Davies (J. Fluid Mech., vol. 663, 2010, pp. 401–433).

Method for quantification of insecticide in mosquito netting using ion implantation and ToF-SIMS analysis

Permethrin is used worldwide as a mosquito insecticide for netting and fabric. Permethrin is a contact insecticide so only the permethrin on the surface can directly impact the mosquito. Therefore, knowledge of the surface concentration of the insecticide is essential to measure the effectiveness of the treated material. Time-of-flight secondary ion mass spectrometry analysis of permethrin showed Cl− as the predominant species in the negative ion mass spectrum. The netting material in this study is composed of high density polyethylene (HDPE). Ion implantation was used to place a known amount of chlorine into the netting material, sheet HDPE, and silicon samples. Depth profile analysis of the implanted samples showed distinct chlorine implant profiles, with the silicon sample used to verify implant dose. Quantification and detection limit for chlorine have been obtained for HDPE sheet and netting. The chlorine detection limit in HDPE is approximately 2 × 1018 atoms/cm3, and the chlorine concentration in netting fibers ranged from 4 × 1019 to 1.2 × 1020 atoms/cm3, which compares very well with the amount of insecticide put into the netting during fabrication. The results make possible the study of insecticide content at the surface and in the bulk of the netting. Investigation is in progress for the effect of washing mosquito nets on surface chlorine concentration.

A modular large-area lithium foil multi-wire proportional counter neutron detector

Abstract Several Li foil multi-wire proportional counters were constructed with five layers of 75 µm thick 6 Li foils spaced 1.63 cm apart. Each detector had 1250 cm 2 of active area and was backfilled with 1.0 atm of P-10 gas. Two of these detectors were positioned back-to-front with 5.0 cm of high-density polyethylene (HDPE) positioned between the two detectors and on the front and back. Additional 2.54 cm thick HDPE sheets were added to the remaining sides. The detectors were operated with a single electronics unit and were delivered to a test facility where multiple neutron and gamma-ray sensitivity experiments were completed. First, a 252 Cf neutron source was positioned at various distances from the front of the detector and the absolute detection efficiency (cps ng −1 ) was recorded at each distance. Second, a transient test was completed by moving the neutron source in front of the detector at a constant rate while recording the change in count rate (cps). Third, the lateral sensitivity and symmetry of the detection system was investigated by positioning a 252 Cf source up to 5.0 m away from the centerline of the arrayed detectors in 1.0 m increments in both outward directions. The angular response was investigated by positioning the 252 Cf source 2.0 m from the center of the device and recording the count rate at each stationary position in 15° increments from 0° to 360°. The count rate varied 15% from minimum to maximum during the angular response test. Additionally, the arrayed system was modeled in MCNP6 and had an intrinsic neutron detection efficiency of 12.6% for a bare 252 Cf source, less than the experimentally determined efficiency of 13.9±0.03%, as expected. The gamma-ray sensitivity of the detection system was also investigated and pulse-height spectra were collected and plotted against a neutron response spectrum for comparison.

Microstructure-property characterization of a friction-stir welded joint between AA5059 aluminum alloy and high density polyethylene

Aluminum alloys and high density polyethylene are utilized in a wide variety of industrial applications. In the present work the feasibility of friction stir butt welding between AA5059 alloy and high density polyethylene sheets is examined. The bonding mechanism, joint strength, and microhardness are considered in this study. Various welding parameters and tool alignment were investigated until sound joints were achieved by positioning approximately 85% of the rotating tool in the aluminum material on the advancing side (1.4mm offset) at constant spindle speed and traverse speed of 710rpm and 63mm/min, respectively. The results indicate that AA5059 aluminum and high density polyethylene sheets can be successfully joined with a combination of secondary bonding and mechanical interlocking of the materials, which provides a potential alternative to adhesive bonding or mechanical fastening.

Evaluation of various polyethylene as potential dosimeters by attenuated total reflectance-Fourier-transform infrared spectroscopy

Abstract Various types of polyethylene (PE) have been evaluated in the past for use as a potential dosimeter, chiefly via the formation of an unsaturated transvinylene (TV) double-bond resulting from exposure to ionizing radiation. The utilization of attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy in characterizing TV formation in irradiated PE for a potential dosimeter has yet to be fully developed. In this initial investigation, various PE films/sheets were exposed to ionizing radiation in a high-energy 5 megaelectron volt (MeV) electron beam accelerator in the 10–500 kilogray (kGy) dose range, followed by ATR-FTIR analysis of TV peak formation at the 965 cm −1 wavenumber. There was an upward trend in TV formation for low-density polyethylene (LDPE) films and high-density polyethylene (HDPE) sheets as a function of absorbed dose in the 10–50 kGy dose range, however, the TV response could not be equated to a specific absorbed dose. LDPE film displayed a downward trend from 50 kGy to 250 kGy and then scattering up to 500 kGy; HDPE sheets demonstrated an upward trend in TV formation up to 500 kGy. For ultra-high molecular weight polyethylene (UHMWPE) sheets irradiated up to 150 kGy, TV response was equivalent to non-irradiated UHMWPE, and a minimal upward trend was observed for 200 kGy to 500 kGy. The scatter of the data for the irradiated PE films/sheets is such that the TV response could not be equated to a specific absorbed dose. A better correlation of the post-irradiation TV response to absorbed dose may be attained through a better understanding of variables.

In vitro and in vivo evaluation of a new nanocomposite, containing high density polyethylene, tricalcium phosphate, hydroxyapatite, and magnesium oxide nanoparticles

In this study, a new nanocomposite, which contained high density polyethylene (HDPE), tricalcium phosphate (Ca3(PO4)2) nanoparticles (TCP NPs), hydroxyapatite nanoparticles (HA NPs), and magnesium oxide nanoparticles (MgO NPs) was prepared. As in vitro experiment, human osteoblasts (HOB) cells were exposed to pristine HDPE and its nanocomposite for a period of 1, 4, and 7days at 37°C, and then different assays were carried out, including osteoblast cell proliferation, Trypan blue staining, cell viability, alkaline phosphatase (ALP), and cell adhesion. Antibacterial property of pristine HDPE and its nanocomposite was evaluated, and also their mechanical properties were measured after 2 and 4months. As in vivo experiment, pristine HDPE and its nanocomposite were separately implanted on calvarium bone of rabbits, and tissue inflammation and osteogenesis were investigated after 2, 4, and 6months. In case of HOB cells treated with HDPE or nanocomposite, as incubation time was increased, cell proliferation, live/dead ratio, and cell viability were decreased. But, the ALP activity and cell adhesion of HOB cells which treated with nanocomposite were raised after increase of incubation time. This study demonstrated that although the mechanical properties of nanocomposite were similar to HDPE sheet, but their antibacterial property was not similar. The in vivo experiment showed that both pristine HDPE and its nanocomposite had same inflammation responses. Interestingly, osteogenesis was observed after 2months at bone/nanocomposite interface, and was highly increased after 4 and 6months. It must be noted that such pattern was not seen at bone/HDPE interface.

Oriental Nose Elongation Using an L-Shaped Polyethylene Sheet Implant for Combined Septal Spreading and Extension

The currently recommended strategies for short nose elongation were designed primarily for the Caucasian nasal framework. For Oriental patients, more elongation often is required because a hypoplastic septal cartilage requires more elongation, resulting in a higher risk of complications. This report proposes a modified technique for Oriental nose elongation, which adjusts the pressure points after nasal elongation using an L-shaped implant. Between January 2007 and December 2009, 58 patients underwent Oriental nose elongation using an L-shaped, porous, high-density polyethylene sheet implant. Augmentation rhinoplasty and conchal cartilage shield grafts were performed depending on the nasal shape. Pre- and postoperative nasal length, height, and projection as well as columella-labial angle, columella-lobular angle, and nasal tip angle were measured and compared. A patient satisfaction survey was performed postoperatively. All occurring complications were recorded. The postoperative nasal length was significantly elongated from 47.0±10.4 mm to 49.3±10.1 mm (p=0.003), and the nasal height increased significantly from 48.5±9.1 mm to 50.4±8.5 mm (p=0.011). The initially obtuse columella-labial angle improved significantly from 100.8°±12.1° to 92.5°±15.5° (p=0.014). No significant changes were found regarding nasal projection, nasal tip angle, or columella-lobular angle. The majority of the patients (91.3%) were highly satisfied or satisfied with the aesthetic results. A major complication in terms of implant exposure was observed in one case. The minor complications included stiffness of the nasal tip (3 patients) and tip redness (1 patient). In Oriental nose elongation, the use of an L-shaped graft is a feasible and safe treatment option that allows for an excellent aesthetic outcome and reduces the incidence of complications. This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Experimental investigation on flexural behavior of friction stir welded high density polyethylene sheets

Flexural strength is one of the main criteria in evaluation of the mechanical properties of polymeric joints. The flexural strength of thermoplastics, such as high density polyethylene (HDPE) sheets, is influenced by friction stir welding parameters. The determination of the welding parameters plays an important role in the weld strength. In the present study, the response surface method (RSM) was used as a statistical design of experiment technique to set the optimal welding parameters. The designed tool was consisted of a rotating pin, a stationary shoulder (shoe) and a heating system inside shoe. Rotational speed of the pin, tool traverse speed and shoe temperature were considered as varying parameters. Obtained results show a significant relationship between considered properties and processing parameters through an analysis of variance (ANOVA) study and the response surface method. It was found that welding at a high level of rotational speed and a lower level of tool travel speed increases weld flexural strength by reducing size of defects.

OPTIMIZATION OF FRICTION STIR WELDING PROCESS PARAMETER USING TAGUCHI METHOD AND RESPONSE SURFACE METHODOLOGY: A REVIEW

Friction stir welding (FSW) is relatively new solid state joining process. This joining technique is e nergy efficient, environment friendly and versatile. Welding is a multiinput-out put process in which quality of welded joint is dep ends upon a input parameter. Therefore optimization of input process parameter i s required to achieve good quality of welding. Ther e are so many methods of optimization in which Taguchi method and Response s urface methodology are selected for optimization of process parameter. In this review the effect of process parameter on welded jo int studied and optimizes the parameter by using Ta guchi method and Response surface methodology. The study of Friction stir wel ding of Aluminium alloy and High density polyethyle ne sheets shows the improvement in welded joint quality by optimization of process parameter. The main process parameters which affect the strength of welded joint is tool rotational speed, welding sp eed, axial force and tool pin profile.

Confinement effect of geocells on sand samples under triaxial compression

The confinement effect of geocells improves vastly the shear strength of granular soil. To understand the mechanism better, several tests have been performed on geocell-reinforced-sand samples of two different sizes. The geocells were made of high-density polyethylene sheets, and the influencing factors examined include the shape (circular, rectangular, and hexagonal cross-sections), size and number of cells. The effects of these variables on the compression strength of samples as well as the stress–strain behavior were investigated. It has been found that the apparent cohesion of reinforced samples vary with the shape, size and number of cells, of which the cell size is the most significant factor. Among the cells of all shapes, the circular cells induce the highest apparent cohesion. In addition, the effectiveness of the reinforcement is more significant at low confining pressure. This can be explained by theoretical analysis, which shows that the reinforced samples under low confining pressures tend to expand more and induce higher circumferential strain. When under high confining pressure, the samples undergo lesser dilation leading to lower hoop forces in geocells.

Comparative Analysis of the Surface Functionalization and Texturization of HDPE after H<sub>2</sub> and O<sub>2</sub> Ion Plasma Immersion

An in-house constructed Plasma Enhanced Chemical Vapor Deposition (PECVD) facility was used in this study to facilitate the surface chemistry improvement on High Density Polyethylene (HDPE) sheets and allow an increase in adhesion of copper thin films on HDPE sheets. The material’s wet ability and polymer-metal adhesive strength are compared before and after plasma treatment to understand the creation and rearrangement of the functional groups present on the surface of H2 and O2 ion irradiated HDPE sheets. Results showed the detection of O-H, C≡C, C═C and C-O bonds on the surface of the irradiated samples. H2 ion irradiated sheets, however, showed no surface chemical functionality changes.