High-density Polyethylene Samples Research Articles

Fabrication, Structural Characterization, and Photon Attenuation Efficiency Investigation of Polymer-Based Composites.

Experiments have assessed various polymer composites for radiation shielding in diverse applications. These composites are lighter and non-toxic when compared to lead (Pb), making them particularly effective in diagnostic imaging for shielding against low-energy photons. This study demonstrates the fabrication of four composites by combining a base material, specifically a high-density polyethylene (HDPE) polymer, with 10% and 20% silicon (Si) and silicon carbide (SiC), respectively. Additionally, 5% molybdenum (Mo) was incorporated into the composites as a heavy metal element. The composites obtained were fabricated into 20 disks with a uniform thickness of 2 mm each. Discs were exposed to radiation from a low-energy X-ray source (32.5-64.5 keV). The chemical and physical properties of composites were assessed. The shielding ability of samples was evaluated by determining the linear and mass attenuation coefficients (μ and μm), radiation protection efficiency (RPE), half-value layer (HVL), and mean free path (MFP). According to our findings, supplementing HDPE with additives improved the attenuation of beams. The μm values showed that composite X-ray shielding characteristics were enhanced with filler concentration for both Si and SiC. Polymer composites with micro-molecule fillers shelter X-rays better than polymers, especially at low energy. The HVL and MFB values of the filler are lower than those of the pure HDPE sample, indicating that less thickness is needed to shield at the appropriate energy. HC-20 blocked 92% of the incident beam at 32.5 keV. This study found that increasing the composite sample thickness or polymer filler percentage could shield against low-energy radiation.

Reinforced HDPE with optimized biochar content for material extrusion additive manufacturing: morphological, rheological, electrical, and thermomechanical insights

The development of efficient and sustainable composites remains a primary objective of both research and industry. In this study, the use of biochar, an eco-friendly reinforcing material, in additive manufacturing (AM) is investigated. A high-density Polyethylene (HDPE) thermoplastic was used as the matrix, and the material extrusion (MEX) technique was applied for composite production. Biochar was produced from olive tree prunings via conventional pyrolysis at 500 °C. Composite samples were created using biochar loadings in the range of 2.0–10.0 wt. %. The 3D-printed samples were mechanically tested in accordance with international standards. Thermogravimetric analysis (TGA) and Raman spectroscopy were used to evaluate the thermal and structural properties of the composites. Scanning electron microscopy was used to examine the fractographic and morphological characteristics of the materials. The electrical/dielectric properties of HDPE/biochar composites were studied over a broad frequency range (10–2 Hz–4 MHz) at room temperature. Overall, a laborious effort with 12 different tests was implemented to fully characterize the developed composites and investigate the correlations between the different qualities. This investigation demonstrated that biochar in the MEX process can be a satisfactory reinforcement agent. Notably, compared to the control samples of pure HDPE, biochar increased the tensile strength by over 20% and flexural strength by 35.9% when added at a loading of 4.0 wt. %. The impact strength and microhardness were also significantly improved. Furthermore, the Direct current (DC) conductivity of insulating HDPE increased by five orders of magnitude at 8.0 wt. % of biochar content, suggesting a percolation threshold. These results highlight the potential of C-based composites for the use in additive manufacturing to further exploit their applicability by providing parts with improved mechanical performance and eco-friendly profiles.Graphical

Gamma-ray shielding effectiveness, thermal, and dielectric properties of filler-reinforced high-density polyethylene/boron carbide composites

The present research prepared samples of pure high-density polyethylene (HDPE)/boron carbide reinforced with iron dioxide, aluminum dioxide, iron, and aluminum. The effectiveness of the prepared samples as a shielding material against gamma-rays and their thermal and dielectric properties have been evaluated. The shielding characteristics of the prepared composites were investigated theoretically using the Phy-X/PSD program and experimentally for gamma-rays emitted from 131Cs and 60Co radioactive isotopes. The shielding evaluation included the mass attenuation coefficient (μ/ρ), half value layer (HVL), mean free path (MFP), atomic and electronic cross-sections (σa&σe), effective atomic number and electron density (Zeff &Neff), and exposure build-up factor (EBF). The EBF peaks of samples containing Fe and Fe2O3 are 103 times lower than pure HDPE. The results indicate that samples C2 and C3 have a higher ability to protect against gamma radiation than that of the other investigated samples. X-ray diffractometer (XRD) spectrum shows that adding B4C, Fe, Fe2O3, Al, and Al2O3 to HDPE caused an increase in its full width at half maximum (FWHM) value and a decrease in its average crystallite diameters (D) at its primary characteristic scattering angle of 21.49°. Adding multiple types of fillers to HDPE results in a minor shift in the melting temperature of the hosting matrix as proved from differential scanning calorimetry (DSC) data. The composite of HDPE/B4C/Al2O3 60/10/30 demonstrated the most significant values of dielectric parameters in comparison with the other composites, in good accord with the XRD results. The ac conductivity relied on the dopant type in the hosting matrix; the highest value was observed for HDPE/B4C/Al2O3 composite.

Influence of trimodal polymerization on melt rheology, thermal, and mechanical properties of HDPE resin

AbstractTrimodal polymerization of polyethylene has become a research interest in recent years due to its excellent potential for altering material properties and overcoming the limitations of the bimodal process. Here, we have comprehensively investigated the effects of manipulating polymerization parameters, such as split value (SV), hydrogen‐to‐ethylene ratio (H2/C2), and stage switching, on the rheological, thermal, and mechanical properties of synthesized trimodal high‐density polyethylene (HDPE). The synthesized samples were obtained through three consecutive stages in a slurry lab‐scale reactor. The results of molten state analysis demonstrate that recipe modification, particularly SV and H2/C2 balancing in the second and third stages, had a dramatic effect on the rheological properties including dynamic moduli, G′‐G″ crossover, and the shear‐thinning behavior. Concurrently, improvements in physio‐mechanical properties, such as sagging behavior and slow crack growth resistance (SCG), were observed compared to the bimodal resin. The thermal characterization indicates that the polymerization adjustments made did not notably impact the thermal properties of HDPE samples (e.g., Tm), throughout the all‐recipe manipulation. However, minor fluctuations in crystallinity and crystallization kinetics were observed which was presumably attributed to the molecular weight of the final resin. Overall, in our trimodal polymerization recipe, the HDPE powder is within the specified range of particle size distribution, which ensures excellent bulk density and flowability.Highlights Influence of polymerization parameters such as split value, H2/C2, and stage switching in properties of trimodal HDPE. HDPE resin received from split value and H2/C2 balancing have superior SCG and sagging resistance. All HDPE samples synthesized by different recipes have similar thermal properties.

The evidences for the existence of evanescent wave-induced scattering in the transmission SAXS of high-density polyethylene

In an earlier study of ours (Li et al., IUCrJ,2019 6, 968–983), we conjectured that small-angle X-ray scattering (SAXS) in semicrystalline polymers might be from evanescence wave-induced scattering (Ievi) rather than claimed by classical scattering theory, the incident X-ray-induced scattering (Iin). In this study, we systematically compared Ievi and Iin under the influence of various factors, i.e., linear crystallinity, the number of lamellar crystals (N), the characteristic penetration depth of evanescent wave (dp*) and long period distribution, identifying the method to distinguish SAXS in semicrystalline polymers is from Iin or Ievi. Applying this method to SAXS of a high-density polyethylene (HDPE) sample, it was found that even excluding the influence of instrumental broadening and lamellar thickness/long period dispersity, the SAXS peak in HDPE is still greater than theoretically maximum peak width induced by Iin, indicating the SAXS in HDPE is not induced by incident X-ray directly. Excluding the interference of long period dispersity, it was found that dp* was around 5.9 nm, clearly demonstrating the existence of evanescent wave. Besides, results indicated that the lateral size determined with new theory is accurate, which in turn demonstrated that our assumption that Ievi is from a lamellar stack parallel to incident X-ray is reasonable. Taking all evidences together, it can be concluded safely that SAXS in HDPE is induced by evanescent wave.

Study of radiation attenuation properties of HDPE/ZnO at energies between 47.5 and 266 keV

Seven different composites of high-density polyethylene (HDPE) were fabricated as potential flexible, lightweight and non-toxic radiation shields based on zinc oxide (ZnO) concentrations of 0%, 2%, 4%, 6%, 8%, 10% and 12%. The linear and mass attenuation coefficient (μ, μm), radiation protection efficiency (RPE) and mean free path (MFP) of the proposed HDPE-based composites were estimated. The shielding parameters, including μ, μm, RPE and MFP, of the seven samples were determined utilising eight X-ray standard radiation qualities (N-60 to N-300) at voltages of 60, 80, 100, 120, 150, 200, 250 and 300 kVp for effective energies of 47.5, 67.6, 83.3, 100, 126, 166, 218 and 266 keV, respectively. The μ results of the seven HDPE composite materials were between 0.1188 cm−1 and 0.4788 cm−1. The 12% HDPE/ZnO sample has the highest attenuation across all incident X-ray beam energies among the selected composites. The result revealed that the measured μm results align with the theoretical XCOM results for all samples, with an average error of 3.39%. Additionally, a composite containing 12% ZnO had a minimum MFP value and the highest percentage of RPE obtained from a 12% HDPE/ZnO sample with about 38.05%, compared with 17.09% of pure HDPE sample at 47.5 keV energy. This work concludes that adding ZnO to the HDPE polymer increases its shielding effectiveness for X-rays at these low energies, commonly used in radiation research and hospitals' radiology departments. In addition, increasing either the thickness or the ZnO concentration in the samples could enhance its practical usage as a radiation shield.

Crystallinity and Oscillatory Shear Rheology of Polyethylene Blends.

Crystallinity and rheological behavior are significant for processing semi-crystalline polymers with fine mechanical properties. There is always an economical need to create a less expensive new material with better properties. Non-isothermal crystallization and oscillatory shear rheology of different branch-type polyethylene-polyethylene blends were investigated. Samples of high-density and low-density polyethylene (HDPE/LDPE) (20/80, 40/60, 60/40 and 80/20 weight ratios) and two types of high-density and linear low-density polyethylene (HDPE/LLDPE) (40/60 and 60/40 weight ratios) were prepared via extrusion. The materials were tested by differential scanning calorimetry (DSC) at several cooling rates (5, 10, 20, 30 and 40°/min) and by oscillation rheometry (ARES G2) at low angular frequency range to prove their miscibility or immiscibility. It was found that the one-peak melting endotherm of the 80-20% HDPE-LDPE blend could indicate miscibility in the solid phase, while the other HDPE-LDPE blends with two-peak curves are partially or not miscible. In contrast, all the HDPE-LLDPE blends indicate co-crystallization, but the 40-60% HDPE-LLDPE butylene blend is probably immiscible. It was revealed that complex viscosity decreases with angular frequency: linearly for HD-LD blends and not linearly for HD-LLDPE blends. The complex viscosity shows linear behavior with composition for HD-LLDPE blends, while there is a positive-negative deviation for HD-LD blends. In the liquid phase, according to rheological measurements, the HDPE-LDPE blends are not or partially miscible, while the HDPE-LLDPE blends are probably miscible.

Thermal degradation of virgin and waste plastics: Estimation of kinetic and thermodynamic parameters using model‐free iso‐conversional methods

AbstractKinetic triplets—apparent activation energy (Ea), pre‐exponential factor (A), and the reaction model—were estimated for the thermal degradation of three primary virgin and waste plastics, as well as mixed plastics waste. Model‐free iso‐conversional FWO, KAS, Starink, Kissinger and Vyzovkin and Friedman methods were employed for the kinetic analysis. The apparent activation energy was determined by the integral methods as 206.5‐209.1 kJ mol−1 and 195.6‐198.8 kJ mol−1 for the virgin and waste high‐density polyethylene (HDPE), 211.6‐214.1 kJ mol−1 and 183.1‐186.6 kJ mol−1 for the virgin and waste polypropylene (PP), 144.0‐163.1 kJ mol−1 and 159.7‐167.1 kJ mol−1 for the virgin and waste polystyrene (PS), and 173.6‐178.9 kJ mol−1 for the mixed plastics waste respectively. Ea was found to follow the trend HDPE > PP > PS with higher values for HDPE and PP virgin samples than that for their waste and marginally smaller for the virgin PS than its waste. Degradation of all plastic samples followed Avrami‐Erofeev equation with n varying between 1.0 and 1.8. The effect of conversion on Ea suggested the degradation of both virgin and waste HDPE to consist of multiple parallel reactions while that of others to be more complex. FTIR analysis of the evolved gases was used to explain the possible reaction mechanism. A small difference between the enthalpy change and the apparent activation energy (6‐7 kJ mol−1) for all plastic samples indicated favourable pyrolysis reactions. The estimated kinetic parameters and thermodynamic properties showed the stability of different plastics as HDPE > PP > PS.

Study of a Conical Plasma Jet with a Cloth-Covered Nozzle for Polymer Treatment.

Although atmospheric pressure plasma jets (APPJs) have been widely employed for materials modification, they have some drawbacks, such as the small treatment area (couple of cm2). To overcome this limitation, a funnel-like APPJ with a wide exit has been proposed. In this work, a gas-permeable cotton cloth covered the nozzle of the device to improve the gas flow dynamics and increase its range of operation. The funnel jet was flushed with Ar, and the plasma was ignited in a wide range of gas flow rates and the gap distances between the exit nozzle and the sample holder. The device characterization included electric measurements and optical emission spectroscopy (OES). To evaluate the size of the treatment and the degree of surface modification, large samples of high-density polyethylene (PE) were exposed to plasma for 5 min. Afterward, the samples were analyzed via water contact angle WCA measurements, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It was found that surface modification occurs simultaneously on the top and bottom faces of the samples. However, the treatment incorporated different functional groups on each side.

Thermal expansion of high‐density polyethylene in hot plate welding applications

AbstractThis research studies high‐density polyethylene (HDPE) behavior that is not easily identifiable in a production setting, but is, nevertheless, necessary for consideration when specifying equipment performance for hot plate welding (HPW) applications. Thermal expansion in polymers can depend on several factors, such as the specific type of polymer, its degree of cross‐linking, and the temperature range over which the expansion occurs. This physical behavior can affect the process by prolonging the cycle time if the equipment is not sized correctly for the application. This research uses HDPE samples with different surface areas and varying process parameters (force and temperature) to collect data on the sample size change. Experimental results are compared with a recommended industrial guideline of 0.2 to 0.5 MPa of pressure for the Matching stage (stage for surface conformation). Obtained findings indicate that this industrial guideline is very temperature dependent. Data collected in the experiment were used to develop a mathematical model for thermal expansion under different parameters. This study also presents a visual interpretation of HDPE behavior on the effect of temperature if the pressure is increased or decreased.

High density polyethylene and butanol-gasoline blends: A material compatibility study

We are now well on the path of transitioning away from the fossil fuel resources on cutting down their consumption as much as possible. The fuels chosen for this study include ethanol-butanol (EB) -gasoline, acetone-butanol-ethanol (ABE) -gasoline and methanol-butanol (MB) -gasoline blends. High density polyethylene (HDPE) is a polymer that is extensively used in several auto parts and fuelling infrastructure materials. Incompatibility between these blends and fueling infrastructure system should be studied comprehensively for the adoption of these alternative fuels to be faster and hassle free. This study intends to gauge the changes in HDPE because of its immersion in the gasoline-alcohol blends mentioned for a period of 4, 30 & 90 days. The changes were ascertained by studying the mass, tensile strength, elongation, and hardness of the samples before and after immersion into blends. Sophisticated techniques were used to characterize the morphological and chemical changes of the polymer. The results showed that there was an increase in the mass of the HDPE samples as a result of the absorption of the blends by the polymeric samples. A decrease in tensile strength and hardness values were recorded for the samples whereas the elongation values were found to increase. Studies revealed that there was neither fuel degradation nor any oxidative degradation of the polymeric sample. The results indicated an increase in the mass and elongation of the HDPE as a result of the absorption of the fuel leads to lesser stable polymeric matrix and decrease in the percentage crystallinity. Hence this investigation led us to the conclusion that all the fuels blends studied are highly compatible with HDPE, even in instances where a change in the mechanical properties is seen, it is similar to that seen in gasoline.

Polyethylene Incorporating Diels-Alder Comonomers: A "Trojan Horse" Strategy for Chemically Recyclable Polyolefins.

Polyolefins with periodic unsaturation in the backbone chain are sought after for synthesizing chemically recyclable polymers or telechelic polyolefin macromonomers. Here we introduce a bottom-up synthesis of unsaturated high-density polyethylene (HDPE) via copolymerization of ethylene with dimethyl 7-oxabicyclo[2.2.1]hepta-2,5-diene-3,5-dicarboxylate followed by post-polymerization retro-Diels-Alder to unveil hidden double bonds in the polymer backbone. The incorporation of this "Trojan Horse" comonomer was varied and a series of unsaturated HDPE polymers with block lengths of 1.2, 1.9, and 3.5 kDa between double bonds was synthesized. Cross metathesis of unsaturated HDPE samples with 2-hydroxyethyl acrylate yielded telechelic ester terminated PE macromonomers suitable for the preparation of ester-linked PE. These materials were depolymerized and repolymerized, making them suitable candidates for chemical recycling. The ester-linked PE displayed thermal and mechanical properties comparable to commercial HDPE.

Polyethylene Incorporating Diels–Alder Comonomers: A “Trojan Horse” Strategy for Chemically Recyclable Polyolefins

AbstractPolyolefins with periodic unsaturation in the backbone chain are sought after for synthesizing chemically recyclable polymers or telechelic polyolefin macromonomers. Here we introduce a bottom‐up synthesis of unsaturated high‐density polyethylene (HDPE) via copolymerization of ethylene with dimethyl 7‐oxabicyclo[2.2.1]hepta‐2,5‐diene‐3,5‐dicarboxylate followed by post‐polymerization retro‐Diels–Alder to unveil hidden double bonds in the polymer backbone. The incorporation of this “Trojan Horse” comonomer was varied and a series of unsaturated HDPE polymers with block lengths of 1.2, 1.9, and 3.5 kDa between double bonds was synthesized. Cross metathesis of unsaturated HDPE samples with 2‐hydroxyethyl acrylate yielded telechelic ester terminated PE macromonomers suitable for the preparation of ester‐linked PE. These materials were depolymerized and repolymerized, making them suitable candidates for chemical recycling. The ester‐linked PE displayed thermal and mechanical properties comparable to commercial HDPE.

Estimation Method of Molecular Weight of Polyethylene using Terahertz Spectroscopy

This paper uses terahertz (THz) spectroscopy for the first time as a simple method for estimating the molecular weight of a polymer across a very wide range. The viscosity average molecular weight (Mv) was measured and estimated as the molecular weight. Currently, to measure the Mv, a sample is dissolved in a solvent then measured its inherent viscosity. However, this procedure is complicated and time-consuming in practice. Additionally, as the molecular weight increases, the measurement accuracy decreases if Mv of a sample is above 3 million. Therefore, a new simple method is desired. A linear high-density polyethylene sample with an Mv range of 0.1 to 7.4 million was used. THz absorbance spectra of the samples were measured from 50 to 600 cm-1 (1.5 to 18 THz) then the multivariable analysis technique was applied. Consequently, a very high correlation coefficient (R2 ≈ 1) between the estimated and the measured Mv values were obtained across the range of the samples. This method is essential and suitable for industrial applications.

Cross-sectional microstructural analysis to evaluate the crack growth pattern of weathered marine plastics

Fragmentation of degraded plastics and release of smaller secondary microplastics is usually attributed to the growth of environmental stress cracks. Analysis of crack patterns derived from chemical degradation can be useful not only for assessing the cause of plastic fracture and evaluating the useful lifetime of a product, but it can also potentially provide valuable information on the generation of microplastics. However, the literature with respect to microplastics generation is generally limited to surface observations of polypropylene and polyethylene. Here, we used ion-beam milling to prepare cross-sections of fragments of 15 plastic products made from five commodity plastics (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate) that were collected at two beaches in Japan, and then we examined the microstructures of those cross-sections by means of scanning electron microscopy and energy dispersive X-ray spectroscopy. Crack growth in the depth direction was examined to provide insights into microplastic generation behavior. In all of the polypropylene samples, and some of the low-density polyethylene and polystyrene samples, cracks with a depth exceeding 100 μm from the sample surface were observed. Considering that crack growth causes fracture of degraded plastic and microplastic release, these observations suggest the release of sharp-edged microplastics from the crack fracture surface. In contrast, in the high-density polyethylene and polyvinyl chloride samples, crack growth was limited to within 20 μm of the sample surface, suggesting the release of irregularly shaped microplastics and additive particles. The present results suggest that the degradation behavior of plastic products in the depth direction is dependent on the type of plastic.

Effects of combined melt stretching and fast cooling fields on crystallization of high-density polyethylene

In many industrial processes, polymer melt undergoes complex flow-cooling environments before being solidified into the final products. Investigating polymer crystallization under processing conditions is a necessary step to predict and customize the structures and properties of semicrystalline polymers. Herein, the crystallization behavior of high-density polyethylene (HDPE) under combined melt stretching and fast cooling fields was studied through a homemade extensional rheometer. A series of HDPE samples were prepared by cooling the stretched melt at different cooling rates (0.02–220 °C/s) immediately after flow, or after waiting for different times of isothermal crystallization at 128 °C. Microstructural characterizations confirm four different structural states related to the evolution of shish-kebabs after melt stretching, namely generation of shish precursors, shish crystal growth, kebab lamellar growth, and perfection of shish-kebabs, which diversify greatly the structures and morphologies of the final solidified samples. By prolonging the isothermal crystallization time at high temperature, the fast cooling-induced lamellae keep decreasing in thickness. This supports the occurrence of molecular segregation caused by shish-kebabs growth at high temperature, which reduces the molecular weight of the remaining un-crystallized melt. In addition, quantitative analysis of crystalline orientation manifests that the lamellar growth during isothermal process takes strictly the shish as a template and adopts a high orientation, while the fast cooling-induced lamellae are only related to the chains conformation of un-crystallized melt prior to cooling. This work would be essential to advance the in-depth understanding on the actual industrial processing of semicrystalline polymeric materials.

Constructing a parallel aligned shish kebab structure of HDPE/BN composites: Toward improved two-way thermal conductivity and tensile strength

Inspired by the clam-shell structure of pearls, we fabricated thermally conductive high-density polyethylene (HDPE) reinforced by a 2D filler, boron nitride (BN). SEM images showed only lamellae randomly distributed in unshared HDPE samples, whereas a shish-kebab structure was introduced by utilizing an in-house designed rotational shear system. XRD results indicate the BN (002) plane is parallel to the sheared direction. Due to the interconnected shish-kebab structure and aligned BN (002) plane, the Vicat softening temperature was increased from 82.8 °C to 107.9 °C, demonstrating excellent heat resistance under high temperatures. An optimal thermal conductivity of 1.26 W/mK was found at 35 vol% BN loading with a tensile strength of 40 MPa. This work has utilized external force to manufacture HDPE/BN composites with effective thermal dissipation and higher service temperature. The excellent thermo-mechanical properties mean a longer service time and less replaced frequency of material under extreme operating conditions.

Replication Study of Molded Micro-Textured Samples Made of Ultra-High Molecular Weight Polyethylene for Medical Applications

In articular joint implants, polymeric inserts are usually exploited for on-contact sliding surfaces to guarantee low friction and wear, a high load-bearing capacity, impact strength and stiffness, and biocompatibility. Surface micro-structuring can drastically reduce friction and wear by promoting hydrostatic friction due to synovial fluid. Ultra-High Molecular Weight Polyethylene (UHMWPE) is a suitable material for these applications due to its strong chemical resistance, excellent resistance to stress, cracking, abrasion, and wear, and self-lubricating property. However, surface micro-texturing of UHMWPE is hardly achievable with the currently available processes. The present study investigates UHMWPE's micro-textured surface replication capability via injection molding, comparing the results with the more easily processable High-Density Polyethylene (HDPE). Four different micro-texture cavities were designed and fabricated on a steel mold by micro-EDM milling, and used for the experimental campaign. Complete samples were fabricated with both materials. Then, the mold and samples were geometrically characterized, considering the dimensions of the features and the texture layout. The replication analysis showed that HDPE samples present geometrical errors that span from 1% to 9% resulting in an average error of 4.3%. In comparison, the UHMWPE samples display a higher variability, although still acceptable, with percentage errors ranging from 2% to 31% and an average error of 11.4%.

Reversed thermal stability between stress-induced melting and recrystallized crystallites and original inclined ones in moderately stretched ultra high molecular weight polyethylene and high density polyethylene

The structural evolution of tensile stretched ultra high molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) samples to an intermediate strain before the completion of fibrillation upon heating was investigated by means of small-angle X-ray scattering (SAXS) and wide angle X-ray diffraction techniques (WAXD). Six-point SAXS patterns illustrated the existence of two populations of lamellae, one at the inclined direction belonging to the original lamellae experienced deformation of slip processes and another at the tensile direction (meridional lamellae) which were newly formed ones due to fibrillation (stress induced melting-recrystallization). Surprisingly, the inclined lamellae exhibit better thermal stability compared to meridional lamellae in UHMWPE sample, whereas in the HDPE sample the situation is opposite. It turns out that this higher stability of original deformed lamellae at the inclined direction is due to the much higher number of tie chains and more stable entangled amorphous network in UHMWPE which minimizes the surface free energy of those lamellae during heating.

Identification of Microplastics Using a Custom Built Micro-Raman Spectrometer

Microplastics are plastic particles less than 5 mm in size but larger than 0.1 µm. Widespread microplastic pollution in aquatic and terrestrial environment is raising serious concern globally due to its detrimental impacts on living beings. This urge for the necessity of a sensitive analytical tool, which can facilitate reliable identification of microplastics. Micro-Raman spectroscopy enables molecular level structural details of samples and thus highly preferable for the identification of microplastics in water. Besides being a non-destructive technique enabling fast analysis, this technique requires minimal/no sample preparation. The present work demonstrates the performance of a custom built Micro-Raman spectrometer for the discrimination of various microplastics in water based samples. Micro- Raman analysis have been found quite successful in the identification of Polystyrene (PS), Polyethylene terephthalate (PET), High Density Poly ethylene (HDPE), Low Density Poly ethylene (LDPE) etc. The Micro-Raman spectral data have been capable enough for the discrimination of high-density polyethylene (HDPE,> 0.940 g/cm3) and low-density polyethylene (LDPE,< 0.930 g/cm3) microplastics, especially due to the variations in the C-H stretching vibrations (2825-2970 cm−1). The ratio of intensities of asymmetric CH2 stretching mode (2879 cm−1) and the symmetric CH2 stretching mode (2847 cm−1) are found to be higher for HDPE with respect to LDPE. Moreover, intensity variations were also observed for the antisymmetric and symmetric C-C stretching bands present at 1059 cm−1 and 1126 cm−1 respectively. The band at 1167 cm−1 arising from CH vibration have also shown an intensity enhancement in HDPE samples.