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Tanks made of three different brands of rotational polyethylene (DOW, ELTEX, and M350) with three degrees of sintering (normal sintering (NS), incomplete sintering (ICS), and thermally degraded sintering (TDS)) and three thicknesses (7.5 mm, 8.5 mm, and 9.5 mm) were explored. It was found that the thickness of the walls of the tanks did not have a statistically significant effect on the parameters of the ultrasonic signal (USS). An increase in temperature caused a decrease in the USS parameters. According to the temperature coefficient of stability, the ELTEX brand of plastic can be distinguished (from DOW and M350). The ICS degree of the sintering of the tanks was revealed from a significantly lower amplitude of the bottom signal, compared with NS and TDS degree samples. By analyzing the amplitude of the third harmonic of the ultrasonic signal (β), three degrees of the sintering of containers NS, ICS, and TDS were revealed (with an accuracy of about 95%). Equations β = f(T, PIAT) were derived for each brand of rotational polyethylene (PE), and two-factor nomograms were constructed. Based on the results of this research, a method for the ultrasonic quality control of polyethylene tanks manufactured using rotational molding was developed.

Composites suitable for rotational molding technology based on poly(ε-caprolactone) (PCL) and filled with hollow glass microspheres (HGM) or functionalized hollow glass microspheres (HGMf) were prepared via melt-compounding. The functionalization of glass microspheres was carried out by a silanization treatment in order to improve the compatibility between the inorganic particles and the polymer matrix and achieve a good dispersion of glass microspheres in the matrix and an enhanced filler–polymer adhesion. The crystallization behavior of materials was studied by DSC under isothermal and non-isothermal conditions and the nucleating effect of the glass microspheres was proven. In particular, the presence of silanized glass microspheres promoted faster crystallization rates and higher nucleation activity, which are enhanced by 75% and 50%, respectively, comparing neat PCL and the composite filled with 20 wt% HGMf. The crystalline and supermolecular structure of PCL and composites crystallized from the melt was evaluated by WAXD and SAXS, highlighting differences in terms of crystallinity index and structural parameters as a function of the adopted crystallization conditions.

In this work, polypropylene (PP) was foamed via rotational molding using a chemical blowing agent (CBA) based on azodicarbonamide over a range of concentration (0 to 0.5% wt.). The samples were then analyzed in terms of morphological, thermal and mechanical properties. The morphological analysis showed a continuous increase in the average cell size and cell density with increasing CBA content. Increasing the CBA content also led to lower foam density and thermal conductivity. Similarly, all the mechanical properties (tension, flexion and impact) were found to decrease with increasing CBA content. Finally, the efficiency of the rotomolding process was assessed by producing neat PP samples via compression molding. The results showed negligible differences between the rotomolded and compression molded properties at low deformation and rate of deformation indicating that optimal rotomolding conditions were selected.

In this study, foamed recycled high density polyethylene (rHDPE) parts were produced by rotational molding using different concentration (0 to 1% wt.) of a chemical blowing agent (CBA) based on azodicarbonamide. From the samples produced, a complete morphological, thermal and mechanical characterization was performed. The morphological analysis showed a gradual increase in the average cell size, while the cell density firstly increased and then decreased with increasing CBA content. As expected, increasing the CBA content decreased the foam density as well as the thermal conductivity. Although increasing the CBA content decreased both tensile and flexural properties, the impact strength showed a similar trend as the cell density with an optimum CBA content around 0.1% wt. Finally, neat rHDPE samples were also produced by compression molding. The results showed negligible differences between the rotomolded and compression molded properties indicating that optimal rotomolding conditions were selected. These results confirm the possibility of using 100% recycled polymers to produce rotomolded foam parts.

This study presents the structure-property relationship of rotationally molded products made of waste-based polylactide (PLA) pre-processed with different procedures. While the use of recycled petrochemical thermoplastics, such as polyethylene, is a current industrial practice, there is no evidence of recycled, biodegradable polymers as a source of material for manufacturing the rotomolded parts. The main problem is the difficulty in grinding low-melting material with a high ability to degrade during the milling process into a powder, which is essential from the point of view of rotational molding. The work describes three types of polylactide pre-treatment from post-consumer disposable cups for applying powders and micropellet as a material for manufacturing rotationally molded purposes. The applied pre-treatments are annealing disposable cups for 24 h at 100 °C and melt processing by extrusion of previously shredded cups. As part of the conducted research, the influence of initial recrystallization of the polymeric material and the impact of additional melt processing on the geometric features of the charge materials and the degree of their degradation was assessed. Complete structural characteristics of particle-shaped materials (powders and micropellets) evaluated using spectroscopic and calorimetric methods (FTIR and DSC) were related to the structure of the final products assessed by the 3D computed tomography (CT) method and resulting mechanical properties. Based on the conducted analyses, the risks and potential paths of development of the technology of shaping rotomolded products with low porosity (void volume 0.53%) and favorable mechanical properties (tensile strength of 48 MPa), made of recycled, biodegradable polyesters, were shown.

Rotational Molding is a plastic manufacturing process mainly implemented to produce stress free hollow products. Linear Low Density Polyethylene (LLDPE) is widely preferred as base resin for molding roto molded product, but it displays moderate value in some critical applications where strength is the major criteria. Additives can fill the gap in sustaining the necessary strength needed. In the present work, an attempt has been made to analyze the optimum percentage of coir reinforced with LLDPE for rotational molding technique to provide requisite processability for rotational molding process. Coir in its powder form is mixed at concentrations varying in the range of 3% to 20% with respect to LLDPE. In order to justify the prerequisite of processability for rotational molding, various experiments namely FTIR, MFI, rheology and thermal analysis were conducted. FTIR suggested the range of 5% to 15% wherein the significance of LLDPE and coir peaks can be observed. MFI test supported FTIR result which ended in considering 3% to 12% by weight ratio suitable in terms of flow ability. Rheological and thermal analysis subjecting to shear and heat parameter respectively, confirmed the range of 10 weight percentage of coir or below is suitable in terms of material processability. From the experimental results, it is concluded that 10% or less concentration of coir fiber in LLDPE as an optimum range of blend yielding better processability for rotational molding process.

Rotational molding is a plastic manufacturing process that is used to produce seamless, one-piece, and hollow parts by rotating a mold subjected to heat and then cooling it. The aim of this study is to investigate the tensile properties of produced polymeric nanocomposite samples by rotational molding. Linear low-density polyethylene was considered as the polymeric matrix, and nanoclay was added at various weight percentages of 0, 1, and 2 as reinforcement. The effects of weight percentages of nanoclay and processing conditions including rotational speed and processing temperature are investigated on the tensile properties of nanocomposite samples based on the design of experiments according to the L9 orthogonal array of Taguchi approach. Scanning electron microscopy tests were performed on the nanocomposite samples in order to study the possible agglomeration regions of the nanoclays in the polymeric matrix. The results indicate that the processing temperature is the most effective parameter on the tensile strength and Young’s modulus of nanocomposite samples. Tensile strength and Young’s modulus were increased by 21% and 33%, respectively, by increasing the processing temperature. Also, the rotational speed is found to be the second effective parameter on the tensile properties.

In this work, composites based on linear low-density polyethylene and maple wood fibers with and without surface treatment with maleated polyethylene (MAPE) were prepared by dry blending, followed by rotomolding to study the effect of particle size, fiber content, and surface treatment. From the samples produced, a complete characterization of the morphological and mechanical properties was performed. The results obtained showed that MAPE surface treatment improved the fiber–matrix interface quality, which improved the homogeneity, the thermal stability, and the mechanical properties of the composites. The results showed that the effect of particle size was significant as the tensile modulus increased by 7%, 40%, and 73% for 125–250, 250–355, and 355–500 µm at 30 wt% of maple fibers. The tensile strength also increased by 114% at the same fiber loading (30 wt%) when the particle size increased from 125–250 µm to 355–500 μm. Finally, the impact strength with 355–500 µm particles was 52% higher than for 125–250 µm particles at 30 wt%

Rotomolding is a versatile process used in the manufacture of thermoplastic polymeric materials to produce large hollow plastic parts. The aim of this review article was to discuss the rotomolding process and show the properties of the polyethylene composite and rotomolded lignocellulosic fibers, which are processed for prolonged periods under temperature. The main process parameters studied are the shaft speed of the equipment, molding temperature, polymer particle size, polymer melt flow index, and amount of material, which must be well controlled to achieve a non-degraded product with homogeneous thickness and no porosity. Rotomolded composites containing sisal, pine, coir, banana, flax, and maple wood fibers, among others, have been evaluated primarily for their mechanical (impact, flexural, and tensile strength) and morphological properties. The type, content, and treatment of lignocellulosic fillers are the most widely studied variables in polyethylene-based rotomolded composites. Fiber content was the variable that most influenced mechanical properties, particularly impact strength and hardness due to the voids formed by the hydrodynamic volume between the polymer matrix and lignocellulosic filler. Chemical treatment of the fiber by mercerization with NaOH made it more hydrophobic and the addition of maleic anhydride-grafted polyethylene as a coupling agent improved the interfacial adhesion between the non-polar polymer matrix and polar filler. However, the best mechanical property results were obtained with the use of maleic anhydride-grafted polyethylene.

In this work, sustainable rotomolded composites based on green polyethylene (Green-PE) and natural fibers (coir and agave) were studied. Fibers’ surface was treated with maleated polyethylene to improve the fiber-matrix compatibility. Samples were characterized by morphology, mechanical properties (impact, tension, and flexion) and water absorption. Results showed a more homogeneous morphology with better fiber dispersion and wetting in the treated fibers composites which lead to substantial improvements of tensile modulus from 258 MPa for the neat matrix up to 345 MPa for both, treated agave and coir composites (at 30% wt), and tensile strength from 13.7 MPa for Green-PE to 15.3 MPa for 30% treated coir composites. The positive effect of the surface treatment was also observed in flexural strength with increases up to 100% and 34% in flexural modulus. Also, impact strength was increased up to 46% and water absorption reduced up to 55% for treated fiber composites compared to untreated fiber composites. As an important observation, it was possible to obtain similar or even higher mechanical properties with the Green-PE natural fiber composites than for a petroleum-based rotomolded polyethylene, which is interesting in terms of sustainability and performances for specific applications like automotive and packaging.

This paper compares the mechanical properties of different natural fiber composites produced by rotational molding as a way of waste valorization from campaigns to control invasive plant species in Macaronesia. Rotomolded parts produced with polymeric matrices (polyethylene) and filled with up to 20% by weight of cellulosic fibers obtained from Arundo donax L., Pennisetum setaceum, and Ricinus communis plants were characterized in terms of tensile, flexural, and impact strength. It was found that the sieving of natural fibers allowed for their introduction in higher loadings, from 10 (for un-sieved material) to 20%, fiber size greatly affected the mechanical properties of the final parts, although some combinations were proven not to reduce the mechanical properties of the neat resin. This study is a first approach to the valorization of residues obtained from periodic campaigns of the control of invasive species performed by public authorities, usually at the local level. It is important to highlight that the main objective of this research did not focus on economically profitable activity, instead, it was focused on the reduction of wastes to be disposed from ecosystem maintenance actions and the investment of potential income into preservation policies.

Rotational foam molding has attracted more and more attention due to the inexpensive machines required, low residual stresses, and flexible design for special and high-value-added applications. However, it is a great challenge to control cell sizes and morphology because of its coalesce and collapse during prolonged heating or at different temperatures. A novel tailored polyethylene blend with a unique chain structure for rotational foam molding was creatively proposed and demonstrated, and the effects of crystallization temperature and viscosity–temperature sensitivity on foaming were also investigated. The polyethylene blends with few chain branches in the low-molecular-weight part and many chain branches in the high-molecular-weight part effectively improved the crystallization temperature and the viscosity–temperature sensitivity for better prevention of coalesce and collapse during the foam-shaping stage.

In this study, the effects of nanoclay content, rotational speed, and processing temperature on the mechanical properties and thickness uniformity of produced polymeric samples are investigated using rotational molding process. For this purpose, the design of experiments is used according to the L9 orthogonal array of Taguchi approach. Tensile strength, Young’s modulus, hardness, and standard deviation of thickness are considered as different criteria. The results indicate that increasing temperature increases tensile strength and Young’s modulus of nanocomposite samples by 21 and 31%, respectively. Also, the hardness of specimens is increased almost 6% by increasing nanoclay. The thickness uniformity of samples is also improved significantly by increasing nanoclay and processing temperature. Finally, a simultaneous decision analysis is performed and the best sample is selected with respect to the considered criteria using multi-criteria decision making methods. The results illustrate that nanocomposite samples with 1 wt % nanoclay and produced in rotational speed of 23 rpm and temperature of 205°C are the best samples.

In this work, the effects of thermo-oxidative aging on the microstructure and impact properties of polyethylene during the rotational molding process were studied. FTIR and Raman analysis showed that the degradation of polyethylene was responsible for the low-temperature impact strength (LT-IS) and the brittle fracture behavior of samples those subjected to prolonged heating time during rotational molding process. The DSC and polarizing microscope analysis showed that the degradation process was delayed by the addition of antioxidants. Through use and optimization of antioxidants, the thermo-oxidative aging of polyethylene can be modulated, a broader processing window can be achieved, and the products may exhibit better mechanical properties with a wider heating time range.

In this article, the effect of plasma treatment of polyethylene powder and glass fibers on the adhesion between polyethylene and glass fibers in composites prepared by rotational molding was studied. In contrast to other processing techniques, such as injection molding, the rotational molding process operates at atmospheric pressure, and no pressure is added to ensure mechanical interlocking. This makes reinforcing the rotomolded product very difficult. Therefore, the formation of chemical bonds is necessary for strong adhesion. Different combinations of untreated polyethylene (UT.PE), plasma-treated polyethylene (PT.PE), untreated and plasma-treated glass fibers were manually mixed and processed by rotational molding. The resulting composites were cut and tested to demonstrate the effect of the treatment on the adhesion between the composite components and on the mechanical properties of the final composites. The results showed that the treatment of both powder and fiber improved the adhesion between the matrix and fibers, thus improving the mechanical properties of the resulting composites compared to those of pure polyethylene samples and composites prepared using untreated components. The tensile strength, tensile modulus, and flexural modulus of the composites prepared using 10-min treated powder with 20 wt% of 40-min treated fibers improved by 20%, 82%, and 98%, respectively, compared to the pure polyethylene samples.

The lack of suitable destinations for plastics materials can be a global environmental problem. The alternative use of materials for sustainable construction encourages the standardization of waste and promotes effective social, environmental and economic gains at the local level and ensures savings and income for communities. The aim of this paper is the development, manufacture, and characterization of PP and HDPE recycled polyolefin blocks as masonry components in civil construction. These blocks were manufactured by the rotational molding process. Besides this, the mechanical, physical, impact and flammability properties of the blocks were studied. In conclusion, HDPE showed better behavior than PP in tests realized.

The aim of this study was to assess the effect of wood flour addition and the treatment of its surface on the properties and structure of rotationally molded (rotomolded) polypropylene. In this study, a random polypropylene copolymer (rPP) micropellet was rotationally molded with the direct addition of 5 wt % of commercial grade of wood flour Lignocel C120, untreated (WF) and chemically treated (mWF). Part of the natural filler was chemically modified by a silanization process using 3-aminopropyltriethoxysilane (3-APS). The structure, quality and mechanical properties of the polypropylene and composite rotomolded parts were discussed in terms of changes in the material’s thermal properties, evaluated by differential scanning calorimetry (DSC), thermomechanical properties, obtained by dynamic mechanical-thermal analysis (DMTA), and dynamic rheological properties, assessed by oscillatory rheometry. The structure of composites and fillers was analyzed by means of a scanning electron microscopy (SEM), while the analysis of the chemical structure of materials and final products was carried out by a Fourier transform infrared spectrometry (FT-IR). It was found that adding the natural filler, despite the application of a preliminary drying and chemical treatment caused creation of the pores and decreased the overall mechanical properties of the composites. The lower processing ability of the composites was ascribed to a higher complex viscosity and an increase in the elastic behavior of molten composite materials in comparison to pure rPP.

In this work, agave fibers were surface treated using maleated PLA (MAPLA) in order to increase the fiber content (from 10 up to 40% wt.) in polylactic acid (PLA) biocomposites produced by rotational molding and to study the effect of the agave fiber and its treatment on the physical, mechanical and thermal properties of the biocomposites. This chemical modification between agave fibers and MAPLA was evaluated by FTIR spectroscopy. In general the results indicate that MAPLA surface treatment produces a more homogeneous morphology with lower interfacial gaps and overall porosity, especially at higher agave contents. This improved compatibility promoted better stress transfer leading to increased mechanical properties. For example, the tensile strength and modulus of treated fiber composites increased by up to 68% (from 25 to 41 MPa) and 32% (from 1.30 to 1.74 GPa) respectively, in comparison with untreated fiber composites. Fiber surface treatment also decreases hydrophilicity, lowering water absorption and diffusion coefficient. From thermo–mechanical analyses, the damping behavior of the biocomposites decreased with MAPLA treatment since a stronger interface is able to sustain higher stresses and dissipates less energy. Finally, the thermal stability was also improved as a result of better interfacial chemical bonding leading to a 12 °C increase in thermal stability (from 254 to 266 °C).

Motion control parameters of rotational molding can affect process efficiency and product quality. Different motion control schemes will lead to varied powder flow regimes exhibiting different levels of mixing and temperature uniformity. The change in nature of powder flow during a molding cycle suggests that varying the rotational speed could improve the powder mixing and temperature uniformity, therefore potentially reducing processing time and energy consumption. Experiments completed investigating powder flow under uniaxial rotation show that savings of up to 2.5% of the heating cycle time can be achieved. This validates the hypothesis that altering the rotational speed to maintain the ideal powder flow throughout the heating cycle can be utilized to reduce the time taken for all the polymer powder to adhere to the mold wall. The effect of rotational speed on wall thickness uniformity and impact strength were investigated and discussed. Results show a strong influence of rotational speed (and powder flow) on the wall thickness uniformity of the moldings with wall thickness uniformity deviations of up to 50% found (within the 2–35 RPM speed range tested).).

The aim of this study is to investigate a multilayer structure made of polyethylene and polyamide by rotational molding. Due to the different polarity of these polymers, it is difficult to ensure enough adhesion between created layers. Two methods leading to improve adhesion are introduced. Plasma modification of polyethylene powder, after which new functional groups are bound to the treated surface, may enhance specific adhesion by forming hydrogen bonds with-CONH groups of polyamide. Different strategies of adding material to the mold give rise to complicated interlayer which increases joint strength by mechanism of the mechanical adhesion. Mechanical tests show a significant improvement of joint strength, where treated samples reached two-fold values of peel strength (7.657 &plusmn, 1.024 N∙mm&minus, 1) against the untreated sample (3.662 &plusmn, 0.430 N∙mm&minus, 1). During bending test, delamination occurred only in samples that were made of the untreated polyethylene. Adding polyamide during the melting stage of polyethylene powder in rotomolding resulted in the formation of entanglements which improve the peel strength almost eight times in comparison with the sample where the polyethylene was left to completely melt and create smooth interlayer surface.

Innovative composites based on polyethylene (PE) filled with hollow glass microspheres (HGMs) were formulated and successfully prepared as suitable plastic materials for rotational molding technology. The HGMs here used allow to attain lightweight materials with a reduced resin content and appealing aesthetical qualities. To enhance filler dispersion and phase adhesion, thus improving the ultimate properties of the composite materials, two compatibilization strategies were adopted: namely, surface modification of HGMs by dodecyl(triethoxy)silane or addition during mixing of a maleinized PE as in-situ coupling agent. The effectiveness of the surface treatments on HGMs was assessed by attenuated total reflectance Fourier-transform infrared spectroscopy and thermogravimetric analysis investigations. PE-based composites at various HGMs contents (5, 10, and 20 wt%) were prepared by melt blending. Morphology of untreated and modified HGMs, their dispersion in the composites as well as filler/matrix adhesion were investigated by SEM microscopy. Thermal, rheological and mechanical properties of the composites were studied in comparison with neat PE. Rotational molding tests carried out both in laboratory and industrial site demonstrated the feasibility of producing lightweight plastic items (weight reduction up to 17%) of excellent aesthetics on a large scale.

In recent years, foams have experienced a major economic uprise, not least due to their lightweight construction potential. In this article, a new process variation is presented, which enables the generation of foamed structures in rotational molding by the utilization of vacuum. The novel method is based on entrapped air in the melt as an intrinsic physical blowing agent. By applying negative pressure in the cooling or solidification phase, the air bubbles expand. The crystallization freezes the existing conditions and thus forms the foamed structure. The investigations presented consider influences by different pressures as well as the temperature at which the vacuum is applied. The results with polyethylene show that by varying the pressure as well as the application temperature of the vacuum, components with different densities and cell characteristics result. The resulting foamed components excel by an improved stiffness per unit weight ratio.

In this study, blends of poly(lactic acid) (PLA)/linear medium density polyethylene (LMDPE) at different weight ratios were prepared by rotational molding. Two mixing strategies were used to evaluate the effect of phase dispersion on the physical and mechanical properties: (i) Dry-blending (DB) using a high shear mixer, and (ii) melt-blending (MB) using a twin-screw extruder. Thermal, morphological, and mechanical analyses were performed on the neat polymers and their blends. The thermal analysis was completed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and the blends prepared by MB had lower thermal stability than the ones prepared via DB due to some thermo-oxidative degradation through the double thermal process (extrusion and rotomolding). The morphology of the rotomolded parts showed that DB generated larger particle sizes (around 500 &micro, m) compared to MB (around 5 &micro, m) due to the shear and elongational stresses applied during extrusion. The tensile and flexural properties of the rotomolded parts combined the PLA stiffness with the LMDPE toughness independent of the blending technique. Neat PLA presented increments in tensile strength (54%) and flexural strength (111%) for DB compared with MB. A synergistic effect in impact strength was observed in blends with 12 and 25 wt. % of PLA prepared by DB.

This research addresses the importance of pine wood sawdust granulometry on the processing of medium-density polyethylene (MDPE)/wood composites by rotational molding and its effects on the morphological, mechanical and aesthetical properties of parts, aiming to contribute for the development of sustainable wood polymer composites (WPC) for rotational molding applications. Pine wood sawdust was sieved (1000 µm) and analyzed for its physical, morphological and thermal characteristics. Rotational molded parts were produced with matrix/wood ratios from 90/10 to 70/30 wt% considering different wood granulometries. As a natural material, wood changed its color during processing. Granulometries below 500 µm presented better sintering, homogeneity and less part defects. Furthermore, 300–500 µm favored the impact resistance (1316 N), as irregular brick-shaped wood was able to anchor to PE despite the weak interfacial adhesion observed. The increase of wood content from 10 to 30% reduced the impact properties by 40%, as a result of a highly porous structure formed, revealing sintering difficulties during processing. WPC parts of differentiated aesthetics and functionalities were achieved by rotational molding. A clear relationship between wood granulometry and WPC processing, structure and properties was identified., Financial support of the Project RoTMI-Rotomolding Technology and Materials Innovations (POCI-01-0247-FEDER-33095), cofinanced by the European Regional Development Fund (FEDER) through the Operational Program for Competitiveness and Internationalization (POCI) under the “Portugal 2020” framework; to the Portuguese Foundation for Science and Technology (FCT) through the National Funds References UIDB/05256/2020 and UIDP/05256/2020 provided to IPC.

Application of lignocellulosic fillers in the manufacturing of wood polymer composites (WPCs) is a very popular trend of research, however it is still rarely observed in the case of rotational molding. The present study aimed to analyze the impact of wheat bran content (from 2.5 wt.% to 20 wt.%) on the performance of rotationally-molded composites based on a linear low-density polyethylene (LLDPE) matrix. Microscopic structure (scanning electron microscopy), as well as physico-mechanical (density, porosity, tensile performance, hardness, rebound resilience, dynamic mechanical analysis), rheological (oscillatory rheometry) and thermo-mechanical (Vicat softening temperature) properties of composites were investigated. Incorporation of 2.5 wt.% and 5 wt.% of wheat bran did not cause significant deterioration of the mechanical performance of the material, despite the presence of &lsquo, pin-holes&rsquo, at the surface. Values of tensile strength and rebound resilience were maintained at a very similar level, while hardness was slightly decreased, which was associated with the porosity of the structure. Higher loadings resulted in the deterioration of mechanical performance, which was also expressed by the noticeable rise of the adhesion factor. For lower loadings of filler did not affect the rheological properties. However, composites with 10wt.% and 20 wt.% also showed behavior suitable for rotational molding. The presented results indicate that the manufacturing of thin-walled products based on wood polymer composites via rotational molding should be considered a very interesting direction of research.

In this work, the suitability for the production of sustainable and lightweight materials with specific mechanical properties and potentially lower costs was studied. Agave fiber (AF), an agro-industrial waste, was used as a reinforcement and azodicarbonamide (ACA) as a chemical blowing agent (CBA) in the production of bilayer materials via rotational molding. The external layer was a composite of linear medium density polyethylene (LMDPE) with different AF contents (0&ndash, 15 wt %), while the internal layer was foamed LMDPE (using 0&ndash, 0.75 wt % ACA). The samples were characterized in terms of thermal, morphological and mechanical properties to obtain a complete understanding of the structure-properties relationships. Increases in the thicknesses of the parts (up to 127%) and a bulk density reduction were obtained by using ACA (0.75 wt %) and AF (15 wt %). Further, the addition of AF increased the tensile (23%) and flexural (29%) moduli compared to the neat LMDPE, but when ACA was used, lower values (75% and 56% for the tensile and flexural moduli, respectively) were obtained. Based on these results, a balance between mechanical properties and lightweight can be achieved by selecting the AF and ACA contents, as well as the performance and aesthetics properties of the rotomolded parts.

In this work, a simple method is presented to produce ground tire rubber (GTR) -linear low density polyethylene (LLDPE) compounds and foams via rotational molding. In particular, different GTR concentrations (0 to 50% wt.) were dry-blended with different chemical blowing agent (CBA) content (0 to 1% wt.). From the samples produced, a complete set of characterization was performed in terms of mechanical properties (tensile, flexural and impact), density and morphological properties. The results show that increasing GTR content or CBA content not only decreased both tensile and flexural moduli, but decreased ultimate strength and strain at break. As expected, increasing blowing agent content decreased density. Besides, with respect to impact strength, the value of all samples decreased with the addition of GTR or CBA except for 0.2% wt. CBA of GTR-LLDPE composite foams, which nearly remain at the same level.

At present, a two-layered product can be molded through various processes. The rotational molding process is a thermoplastics process that can produce products with a two-layered structure; however, it requires special equipment or additional steps in the processing, which make the processing more complex. However, previous research has shown that, through the use of materials with different particle sizes and melting points, two-layered products can also be molded. Thus, this research uses an axial powder flow apparatus to determine the possibility of a two-layered molding between polypropylene (PP) and linear low-density polyethylene (LLDPE). The differences in the particle shapes of a PP homopolymer and copolymer have been considered. The particle sizes of both PPs were determined to be larger than that of LLDPE, and were mixed in a ratio of 50:50 (%wt) using a dry blending method. The results of this experiment show that the two-layered molding of PP and LLDPE using an uncomplicated technique for rotational molding has a high probability of success.

In this study, the morphological, physical, and mechanical properties of maple fiber self-hybrid composites reinforced linear low-density polyethylene (LLDPE) have been investigated for different concentration (10, 20, and 30%) and ratio (100/0, 75/25, 50/50, 25/75, and 0/100) of short (125–250 μm), medium (250–355 μm), and long (355–500 μm) fibers. Maple surface treatment with a coupling agent (maleated polyethylene, MAPE) was also investigated. The results show that surface treatment increased the tensile modulus and strength, and impact strength. Finally, the self-hybrid composites gave better properties than single size fibers since a positive deviation from the linear law of mixture was observed, especially at 20% wt. For example, a 75/25 ratio of medium/short or long/short fibers produced a tensile modulus and tensile strength between 13% and 33% higher than composites formulated with a single fiber size. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

In this work, the fracture toughness of rotationally molded polyethylene (PE) and polypropylene (PP) was measured using J integral methods at static loading rates and at room temperature. Two different commercially available rotational molding grades PE and PP were tested in this study which have been used in various rotationally molded products such as small leisure craft, water storage tanks, and so on. Scanning electron microscope (SEM), optical microscope, differential scanning calorimetry (DSC), solid-state nuclear magnetic resonance (solid-state NMR), and X-ray scattering were used to investigate the microstructure, fracture surfaces, and compare toughness properties of these materials. In PE, higher molecular weight and broader molecular weight distribution, larger amorphous and crystal region thicknesses are found to be related to higher toughness values. High molecular weight favors higher number of entanglements that improve fracture energy and broader distribution increases long chain branching of higher molecular weight fractions which creates higher entanglements at the branch sites. Larger amorphous regions promote microvoiding more easily compared to thinner amorphous regions, leading to greater plastic deformation and energy absorption. Higher crystal thickness also contributes to microvoiding in the amorphous region. For PP, greater plastic deformation observed in the fracture surfaces is related to higher fracture toughness values. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

This paper deals with investigations of rotational molding of LLDPE – Fumed Silica (FS) nano composites. The investigations were conducted at an industrial scale using a three arm biaxial rotational molding machine by carefully monitoring the Internal Air Temperature (IAT) within the mold. The effect of 4% FS on powder flow quality (dry flow and bulk density), melt flow quality (Melt Flow Index (MFI), static mechanical properties (tensile strength, modulus, toughness, flexural strength and impact strength) as well as dynamic mechanical properties (storage and loss modulus), along with creep and relaxation were investigated. Morphological studies were conducted to correlate the above findings with the dispersion of the nano particles within the LLDPE matrix.

This article surveys recent and not so recent literature in the field of rotational molding. The mechanisms of heat transfer, sintering and bubble removal are evaluated; as are degradation and dimensional stability. The parameters that affect the surface finish are highlighted and a number of the control systems available to the rotational molding process are mentioned. Improvements in molds and machinery, and the extent to which they reduce cycle times are also described. Finally, the range of materials available to the rotational molding process is examined and recent developments are highlighted. Of particular interest is the rotational molding of liquid polymer systems; which are shown to possess great potential for fulfilling many of rotational molding’s surface quality requirements while simultaneously reducing cycle times.

A pressure vessel design is put forward taking the form of a two-layer bottle, the inner sealing layer of which is made of linear low density polyethylene by rotational molding and the external power layer of which is made by winding an oligomer impregnated roving or moldable filament on the inner layer. It is shown that, to achieve the highest adhesion strength, it is necessary to preliminarily prepare the surface of the polyethylene sample by obtaining a particular microstructure and to use epoxy or polyester oligomers with a viscosity low enough to provide complete filling of the polyethylene sample surface texture.

In this work, novel composites based on poly(&epsilon, caprolactone) (PCL) were prepared and characterized in terms of morphological, thermal, rheological and mechanical properties. Hollow glass microspheres (HGM), alone or surface modified by treatment with (3-aminopropyl)triethoxysilane (APTES) in order to enhance the compatibility between the inorganic particles and the polymer matrix, were used to obtain lightweight composites with improved properties. The silanization treatment implies a good dispersion of filler particles in the matrix and an enhanced filler&ndash, polymer adhesion. The addition of HGM to PCL has relevant implications on the rheological and mechanical properties enhancing the stiffness of the material. Furthermore, the presence of HGM strongly interferes with the crystallization behavior and thermo-oxidative degradation of PCL. The increase of PCL crystallization rate was observed as a function of the HGM amount in the composites. Finally, rotational molding tests demonstrated the possibility of successfully producing manufactured goods in PCL and PCL-based composites on both a laboratory and industrial scale.

This work is aimed at studying the suitability of polylactic acid (PLA) plasticized by two cardanol derivatives, i.e., cardanol and epoxidized cardanol acetate, in rotational molding, for the production of hollow items. For this purpose, plasticized PLA samples were obtained by melt mixing and then processed by a lab-scale rotational molding equipment. For comparison, poly(ethylene glycole), PEG, and plasticized PLA samples were also produced. Despite the very low cooling rates attained in rotational molding, completely amorphous samples were obtained with neat PLA and PLA plasticized by cardanol derivatives. In contrast, PEG plasticized PLA showed a very high degree of crystallinity, as highlighted by DSC and XRD analysis, which made the extraction of the rotomolded box-shaped specimens impossible. The plasticizing effectiveness of cardanol derivatives was proven by tensile testing of rotational molded prototypes, which highlighted the reduced modulus and strength and improved strain to break, compared to neat PLA. Therefore, efficient toughening of PLA can be attained by the use of the two cardanol derived plasticizers, which involves a significant reduction of the polymer glass transition, as well as a reduced increase of the crystallization kinetic. On the other hand, the reduction of the glass transition temperature due to the addition of plasticizer is responsible for significant crystallization effects even during ageing at room temperature, which involves significant embrittlement of the material.

Rotational molding, which is widely used in furnishing, entertainment facilities, automotive and boats, military industry and other fields, is a forming method used to produce hollow thermoplastic products. Temperature is the most important process parameter in the rotational molding process, so accurate temperature modulation and control are undoubtedly the main way to ensure product quality. During the rotational molding process, temperature in the oven is very high. Current temperature measuring device cannot make real-time measurement and cannot provide the necessary reference for accurate temperature modulation and control. This article provides an analysis of a wireless temperature measurement device which is used in high temperature enclosed environment, researches the structure, the barrier principle of the temperature measurement device. Finally, tests have been done to verify the working performance. Accurate monitoring and control of the temperature parameter during the rotational molding process can not only improve the working efficiency and energy efficiency of the rotational molding machine, but also provide the reference to design the rotational molding device and molds.

In this study, the feasibility of obtaining superhydrophobic polyethylene parts by rotational molding has been confirmed. The superhydrophobicity is obtained through the surface modification of the thermoplastic by using a microrough aluminium mold. The treatment used to create the microroughness of the mold was an electrochemical process followed by heating at 180 °C. Once the superhydrophobic aluminium mold has been prepared, several rotomolding cycles were carried out. The mold was then used for obtaining rotomolded test cube parts using a conventional polyethylene grade. The behavior of the parts under a water jet show a superhydrophobic behavior of the surface, fact confirmed by the measurement of contact angles above 145°.

A multilayer material was produced by rotational molding to study the effect of composition on the mechanical behavior of a cylindrical liquid container. The first (outer) layer was a composite of linear medium density polyethylene (LMDPE) with 5, 10, or 15 wt% agave fiber (AF). The core (middle) layer was foamed LMDPE with different amount of foaming agent (0, 0.15, 0.25, 0.5, and 0.75 wt%). Finally, the third (internal) layer was neat LMDPE. This structure was produced to optimize the mechanical properties of the molded parts while decreasing weight with good surface properties. From the morphological analysis, it was observed that the layers are not always well defined because of gas migration, especially from the foamed core to the composite layer. As expected, density increased with fiber content while decreasing with foaming agent concentration. In general, impact strength (Charpy and Gardner) was directly related to the overall density of the part. POLYM. ENG. SCI., 2015. © 2015 Society of Plastics Engineers

Rotationally moldable linear low density polyethylene (LLDPE) is one of the most popular materials used for rotational molding. Yet, incorporation of additives is necessary to improve the mechanical, visco-elastic, thermal as well as melt flow properties of LLDPE. In this article, the influence of fumed silica (FS) nanoparticles on the mechanical properties viz. tensile, flexural, and impact strengths of rotationally moldable LLDPE is investigated. The microstructural studies using SEM were conducted to study the dispersion of FS in LLDPE and correlated with the mechanical properties of the nanocomposites. Dynamic mechanical analysis (DMA) were also carried out to find the time–temperature dependent mechanical properties viz. storage modulus (E'), loss modulus (E”), and tan delta between 1 and 8 wt% of FS. DMA studies were extended to perform accelerated stepped isothermal creep studies to find out the influence of FS in creep strains. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

There exists an important relationship between the temperature fields and the heat utilization efficiency in the oven of rotational molding equipment. If the temperatures at the main locations can be reasonably controlled, then the efficiency of the rotational molding machine can be effectively improved. The main objective of this research project is to carry out numerical simulation and analysis of the velocity field and temperature field in the oven of a shuttle-type rotational molding machine by using the commercial code FLUENT. The machine was selected as the research object owing to its uneven temperature fields and large energy wastage. The simulation results were then verified by experiments. By improving the structure of the outlets of rotational molding machine and by reasonably controlling the temperature distribution in the oven and die, the working temperature can quickly reach the maximum point, and the uniformity of the temperature in the working area can be ensured. The results showed that the molding efficiency and energy efficiency of the rotational molding machine can be improved by controlling the temperature distribution, thereby increasing the production efficiency of rotational molding.

In rotational molding process, polymer powders undergo a cycle of heating, melting, cooling, and subsequent solidification in the mold. Resins, like linear low-density polyethylene (LLDPE), are used in this process on a large scale mainly because of its good mechanical properties and excellent thermal stability. Yet, incorporation of additives is necessary to further improve the visco-elastic, thermal as well as melt flow properties of the resin. This study investigates the effects of nanocomposites of fumed silica (FS) with rotationally moldable LLDPE. Thermal transitions in the LLDPE-FS nanocomposites were investigated and correlated with their melt flow characteristics. The effect on melt processing during rotational molding and compounding, were analyzed by melt flow index and torque rheometry studies. A suitable blend of FS in LLDPE has been recommended for rotational molding based on rheological studies and Dynamic mechanical analysis. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers