Development of new lubricating grease formulations using recycled LDPE as rheology modifier additive

The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate lubricating greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium lubricating greases and its relationship with grease microstructure are discussed in this work. In this way, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These lubricating greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these greases resulting greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases.     

Advances and approaches for chemical recycling of plastic waste

The global production and consumption of plastics has increased at an alarming rate over the last few decades. The accumulation of pervasive and persistent waste plastic has concomitantly increased in landfills and the environment. The societal, ecological, and economic problems of plastic waste/pollution demand immediate and decisive action. In 2015, only 9% of plastic waste was successfully recycled in the United States. The major current recycling processes focus on the mechanical recycling of plastic waste; however, even this process is limited by the sorting/pretreatment of plastic waste and degradation of plastics during the process. An alternative to mechanical processes is chemical recycling of plastic waste. Efficient chemical recycling would allow for the production of feedstocks for various uses including fuels and chemical feedstocks to replace petrochemicals. This review focuses on the most recent advances for the chemical recycling of three major polymers found in plastic waste: PET, PE, and PP. Commercial processes for recycling hydrolysable polymers like polyesters or polyamides, polyolefins, or mixed waste streams are also discussed.     

Study on pyrolysis behavior and kinetics of waste plastics with spent FCC catalyst

Pyrolysis is the most promising method for treating plastic waste since it can convert waste plastics into high value-added products, which have significant application potential. In this study, kinetic and thermodynamic analyses of spent fluid catalytic cracking (FCC) catalysts were performed for testing their applicability in catalytic cracking of mixed plastics. Thermogravimetric analysis data were obtained at different heating rates under an inert atmosphere, and the synergistic effect between the mixed plastics and activation energy reduction before and after pretreatment of the spent FCC catalysts was discussed. Through a variety of model-free methods (Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Kissinger methods), it is proved that the spent FCC catalyst facilitates the reduction in activation energy required for the pyrolysis of plastics, which is reduced by approximately 13% from 278 to 242 kJ/mol. The catalytic performance of spent FCC catalyst was improved after pretreatment, while its activation energy decreased by approximately 21% from 278 to 220 kJ/mol. The Friedman-Reich-Levi method was used to fit the curve, and the number of mechanism functions in plastic pyrolysis was determined according to the slope of the fitting curve. The C-R method was used in combination with the Malek method to determine the optimal mechanism function. Moreover, kinetic parameters of the spent FCC catalyst for catalytic cracking of plastics were obtained via kinetic studies on the pyrolysis of mixed plastics, which provided theoretical guidance for industrialization of plastic pyrolysis.     

Study of the decomposition of low density polyethylene blends with vacuum gas oils: Evolution of the gases

Previous studies focused on the behaviour of different samples of vacuum gas oil (VGO), polyethylene (PE) and vacuum gas oil-polyethylene blends (VGO-PE) in thermal and catalytic pyrolysis, showed that the pyrolysis of the blends goes through two decomposition steps, where the first is related to the elimination of the VGO fraction, and the second to the pyrolysis of PE. Moreover, the presence of catalyst mainly affects the PE decomposition. In this work, the evolution of the composition of the gases evolved in the thermal and catalytic pyrolysis decomposition of VGO, PE and VGO-PE blend with temperature (or time) has been studied by GC/MS. The results agree with the previous studies and allow the behaviour of such systems to be better understood, yielding valuable information for designing processes of plastic recycling by mixing with VGO and the mixture being treated in a unit similar to the industrial fluid catalytic cracking unit.     

Recycling of waste from polymer materials: An overview of the recent works

Polymer recycling is a way to reduce environmental problems caused by polymeric waste accumulation generated from day-to-day applications of polymer materials such packaging and construction. The recycling of polymeric waste helps to conserve natural resource because the most of polymer materials are made from oil and gas. This paper reviews the recent progress on recycling of polymeric waste form some traditional polymers and their systems (blends and composites) such as polyethylene (PE), polypropylene (PP), and polystyrene (PS), and introduces the mechanical and chemical recycling concepts. In addition, the effect of mechanical recycling on properties including the mechanical, thermal, rheological and processing properties of the recycled materials is highlighted in the present paper.     

聚乙烯类废弃塑料延迟焦化方法制取燃料油的研究

通过对比废弃塑料（PE）和渣油的热重曲线（TG/DTG）,研究了两者的热解特性,论证了利用延迟焦化方法处理聚乙烯类废弃塑料的理论可行性;同时通过模拟延迟焦化实验,针对性地考察了废弃聚乙烯延迟焦化及废弃聚乙烯与渣油共延迟焦化的反应特性,采用模拟蒸馏方法分析了燃料油产物的成分组成,探讨了废弃聚乙烯延迟焦化方法制取燃料油的生产可行性。结果表明,PE的主要热解温区为350℃~480℃,渣油的为250℃~460℃,两者的热解特性有很大的相似性。PE热解的液体产物中汽油和柴油馏分达到62％,蜡油馏分为38％;PE热解的气相产物为小分子的烃类和氢气。PE与渣油共延迟焦化的液体产物中汽油馏分明显比渣油单独焦化的增加。     

Pretreatment of Plastic Waste: Removal of Colorants from HDPE Using Biosolvents

Plastics recycling remains a challenge due to the relatively low quality of the recycled material, since most of the developed recycling processes cannot deal with the additives present in the plastic matrix, so the recycled products end up in lower-grade applications. The application of volatile organic solvents for additives removal is the preferred choice. In this study, pretreatment of plastic packaging waste to remove additives using biosolvents was investigated. The plastic waste used was high-density polyethylene (HDPE) with blue and orange colorants (pigment and/or dye). The first step was to identify the type of colorants present in the HDPE, and we found that both plastics presented only one colorant that was actually a pigment. Then, limonene, a renewable solvent, was used to solubilize HDPE. After HDPE dissolution, a wide range of alcohols (mono-, di-, and tri-alcohols) was evaluated as antisolvents in order to selectively precipitate the polymer and maximize its purity. The use of limonene as solvent for plastic dissolution, in combination with poly-alcohols with an intermediate alkyl chain length and a large number of hydroxyl (OH) groups, was found to work best as an antisolvent (1,2,3-propanetriol and 1,2,4-butanetriol), leading to a removal of up to 94% and 100% of the blue and orange pigments, respectively. Finally, three cycles of extraction were carried out, proving the capability of the solvent and antisolvent to be recovered and reused, ensuring the economic viability and sustainability of the process. This pretreatment provides a secondary source of raw materials and revenue for the recycling process, which may lead to an increase in the quality of recycled polymers, contributing to the development of an economical and sustainable recycling process.     

Recycling technology of poly(ethylene terephthalate) materials

Poly(ethylene terephthalate) (PET) has become one of major post consumer plastics wastes, in addition to polyethylene (PE), polypropylene (PP), polystyrene (PS) and poly(vinyl chloride) (PVC). The challenge to large-volume plastics companies is to learn how to collect, separate, reprocess and market their low-cost products and make a profit, too. The effort of PET recycling, however, is the most successful story in the plastic recycling technology, including both reclaim and upgrade of PET waste. Beverage bottles made of PET are recycled more than 20% of the total production. The technology of today can reclaim the post-consumer PET bottles to produce high-quality granulated PET with better than 99% purity. A practical reclaim process for recycling PET bottles (including bottle, HDPE base cup, aluminum cap, liner, label and adhesive) is available by the Center for Plastics Recycling Research in USA. PET recycling process, like for other plastics, can be divided into three categories: incineration, physical recycling, and chemical recycling. To make the plastic recycling business pay requires more than simple recovery and marketing. Greatest profit potential is in upgraded and value-added reclaim products. Upgrading involves compounding with additives to make material more processable, adding reinforcement, or producing extrusions or finished parts from reclaim resins. For instance, a modified injection-moldable resin made from PET bottle scrap is claimed to provide high impact and processability at less cost than competitive materials. It is foreseen that chemical recycling of waste PET bottle becomes feasible if the price of raw material goes up. Three economical processes are involved in this technology: pyrolysis, hydrocracking, and hydrolysis. The hydrolysis process is presently employed to recover the raw material for unsaturated polyester resin manufacture or polyols for the production of polyurethane resin. It is reported in this presentation that polymer concrete could be a huge potential market for chemical reclaim of PET materials, especially for green or mixed-color PET, which are priced lower than colorless PET reclaim materials.     

Gas chromatographic study of the volatile products from co-pyrolysis of coal and polyethylene wastes

The aim of this study was to determine the volatile products distribution of co-processing of coal with two plastic wastes, low-density polyethylene from agriculture greenhouses and high-density polyethylene from domestic uses, in order to explain the observed decrease in coal fluidity caused by polyethylene waste addition. Polymeric materials, although they are not volatile themselves, may be analysed by gas chromatography through the use of pyrolysis experiments. In this way, a series of pyrolysis tests were performed at 400 and 500 degrees C in a Gray-King oven with each of the two plastic wastes, one high-volatile bituminous coal and blends made up of coal and plastic waste (9:1, w/w, ratio). The pyrolysis temperatures, 400 and 500 degrees C, were selected on the basis of the beginning and the end of the coal plastic stage. The organic products evolved from the oven were collected, dissolved in pyridine and analysed by capillary gas chromatography using a flame ionization detector. The analysis of the primary tars indicated that the amount of n-alkanes is always higher than that of n-alkenes and the formation of the alkenes is favoured by increasing the pyrolysis temperature. However, this effect may be influenced by the size of the hydrocarbon. Thus, the fraction C17-C31 showed a higher increase of n-alkenes/n-alkanes ratio than other fractions. On the other hand, the difference between the experimental and estimated values from tars produced from single components was positive for n-alkanes and n-alkenes, indicating that co-pyrolysis of the two materials enhanced the chemical reactivity during pyrolysis and produced a higher conversion than that from individual components.     

Comparison of extraction methods for sampling of low molecular compounds in polymers degraded during recycling

The demand for mechanical recycling of plastic waste results in an increasing amount of recycled polymeric materials available for development of new products. In order for recycled materials to find their way into the material market, high quality is demanded. Thereby, a complete and closed loop of polymeric materials can be achieved successfully. The concept of high quality for recycled plastics imply that besides a pure fraction of e.g. polyethylene (PE) or polypropylene (PP), containing only minor trace amount of foreign plastics, knowledge is required about the type and amount of low molecular weight (LMW) compounds. During long-term use (service-life), products made of polymeric materials will undergo an often very slow degradation where a series of degradation products are formed, in parallel, additives incorporated in the matrix may also degrade. These compounds migrate at various rates to the surrounding environment. The release rate of LMW products from plastics depends on the initiation time of degradation and the degradation mechanisms. For polymers the formation of degradation products may be initiated already during processing, and subsequent use will add products coming from the surrounding environment, e.g. fragrance and aroma compounds from packaging. During recycling of plastics, emissions which contain a series of different LMW compounds may reach the environment leading to unwanted exposure to additives and their degradation residues as well as degradation products of polymers.Several extraction techniques are available for sampling of LMW compounds in polymers before chromatographic analysis. This paper reviews and compares polymer dissolution, accelerated solvent extraction (ASE), microwave assisted extraction (MAE), ultrasound assisted extraction (UAE), super critical fluid extraction (SFE), soxhlet extraction, head-space extraction (HS), head-space solid phase micro extraction (HS-SPME), and head-space stir bar sorptive extraction (HSSE) as appropriate sampling methods for LMW compounds in recycled polymers. Appropriate internal standards useful for these kinds of matrices were selected, which improved the possibility for later quantification. Based on the review of extraction methods, the most promising techniques were tested with industrially recycled samples of HDPE and PP and virgin HDPE and PP for method comparison.     

Mechanisms and kinetics of thermal decomposition of plastics from isothermal and dynamic measurements

The kinetics of decomposition of plastics are of interest from different points of view, i.e. evolution of harmful substances during fires or waste incineration, recovering of chemical raw materials from plastic refuses and designing of recycling procedures. To measure the formal kinetic parameters of the degradation of polymers isothermal and dynamic methods are applied in this work. Dynamic measurements are performed by combined thermogravimetry mass spectrometry (TG-MS), the isothermal measurements are carried out with a new closed loop-type reactor. To evaluate consistent kinetic data from isothermal and dynamic measurements, the energy balance for the sample in dynamic measurements has to be considered to obtain the true sample temperature and heating rate. Subject of this investigation is the exploitation of dynamic and isothermal methods for measuring and interpreting the kinetics of thermal decomposition of plastics. Results for commodity plastics polyethylene and poly(vinyl chloride) (PVC) are presented. The combined application of TG–MS, isothermal experiments in the closed loop-type reactor and DSC leads to new results for the decomposition kinetics of PVC. The dehydrochlorination mechanism at moderate temperature can be distinguished in an endothermal and exothermal part. The benzene formation is identified as a second order reaction. A great advantage of the isothermal method is, that changes in the mechanisms are detectable, i.e. changes in the apparent order of the reaction and the apparent activation energy. From that, new mechanistic aspects of the decomposition kinetics of polyethylene were obtained.     

Degradation of polyolefines during various recovery processes

The purpose of the presented research was the investigation of the stability and differences of degradation of polyolefines during various recycling processes. In modeling the recycling process during melting, extrusion with a one-screw extruder was used. Recycling through selective dissolution was modulated by two different solvents (xylene and a definite mixture of n-alkanes). Materials used for the investigations were polypropylene (PP), low-density polyethylene (LDPE) and high-density polyethylene (HDPE) (Ziegeler-Natta technology with vanadium catalyst). Changes in the chemical structure of polymers were measured with infrared spectroscopy and differential scanning calorimetry (DSC). Flow properties were characterized by melt flow index, and mechanical characteristics by tension. Experimental results show that for PP and HDPE, utilizing all investigated recycling technologies, chain scission prevailed over branching. For the LDPE chain branching was obtained. By the same token, differences in crystallinity (and as follows, in molecular mass) between the same materials, recycled by extrusion and selective dissolution, was obtained. During selective dissolution changes of properties and morphology in dependence of the solvent used were observed with the trend being that the amount of the admixture of n-alkane used in this investigation was more considerable with regard to the amount of material destruction as compared to xylene. Any reduction of the mechanical properties of any of the investigated polymers as a result of the various methods used was comparable.     

Identification of Polyethylene by Differential Scanning Calorimetry: Application to forensic science

A forensic sample consisting of melt-recrystallized polymers that was recovered from the scene of a fire in a factory was identified by differential scanning calorimetry. The factory commonly used two kinds of film sheets, A and B, made by different manufacturers. It was necessary to decide whether the forensic sample related to material A or B. The forensic sample and reference samples of materials A and B were subjected to infrared spectroscopy and pyrolysis gas chromatograph mass spectrometry measurements, which revealed their polyethylene nature. The thermal behaviour of the samples was examined by differential scanning calorimetry (DSC) and they were found to be blends of two kinds of polyethylenes, low-density polyethylene and linear low-density polyethylene. The samples could be identified and distinguished from each other via the DSC measurements.This revised version was published online in November 2005 with corrections to the Cover Date.     

典型城市固体废弃物热解动力学机理研究

利用热重（TGA）技术研究了城市固体废弃物中塑料橡胶类、木质纤维素类、织物类和厨余类四大类可燃组分中七种典型固体废弃物热解反应过程。实验结果表明,塑料类和织物类最难热解,厨余类组分最易热解;采用Freeman-Carroll法对七种典型固体废弃物热解进行数据处理,从20种常用的固相反应机制函数中遴选出最优解,利用优化的数学函数和动力学参数建立动力学模型,结果表明,PE和羊毛线热解主要反应阶段的最优固相反应模型是球形相界面反应模型;橡胶粉、杨树枝热解反应模型遵循化学反应规律;米饭和本白棉布热解曲线遵循幂函数法则;白菜的最优模型是三维扩散模型。     

Chemical Upcycling of Waste Plastics to High Value-Added Products via Pyrolysis: Current Trends,Future Perspectives,and Techno-Feasibility Analysis

Chemical upcycling of waste plastics into high-value-added products is one of the most effective, cost-efficient, and environmentally beneficial solutions. Many studies have been published over the past few years on the topic of recycling plastics into usable materials through a process called catalytic pyrolysis. There is a significant research gap that must be bridged in order to use catalytic pyrolysis of waste plastics to produce high-value products. This review focuses on the enhanced catalytic pyrolysis of waste plastics to produce jet fuel, diesel oil, lubricants, aromatic compounds, syngas, and other gases. Moreover, the reaction mechanism, a brief and critical comparison of different catalytic pyrolysis studies, as well as the techno-feasibility analysis of waste plastic pyrolysis and the proposed catalytic plastic pyrolysis setup for commercialization is also covered.     

Etudes comparatives et identification des polyethylenes par analyses thermique differentielle et de diffraction des rayons X

In thermal analysis polyethylenes can be characterized by their melting temperature. With the polyethylene mixtures studied, we obtained the best results during solidification. Crystallization temperature decreased in the order: high density PE, low density PE linear, radical low density PE.Calorimetric measurement of crystallization enthalpies allowed the determination of the composition of each of the polyethylenes, in regenerated and recycled mixtures in relation with the frame of the plastic waste valorisation process.The rate of crystallization obtained from X-ray diffraction spectra of these polymers is function of their volumic mass.A good agreement has been observed between these two techniques.

     

Influence of additives on recycled polymer blends

Polymer systems based on polymer waste offer promising way to increase recycling in the society. Since fillers play a major role in determining the properties and behavior of polymer composites, recycled polymers can also be combined with fillers to enhance the stiffness and thermal stability. In this study, blends of recycled polyethylene and recycled polypropylene with mica and glass fiber were prepared by melt blending technique. The effect of the particle loading, filler type, and filler–matrix interaction on thermal degradation and thermal transition of processed systems were investigated. Thermogravimetric analysis, differential thermogravimetric analysis, and differential scanning calorimetry were used in this investigation. Comparative analysis shows that both fillers produced different effects on thermal properties of the processed systems. These results were confirmed by calculating the activation energy for thermal degradation and thermal transition using Kissinger and Flynn–Wall expressions.     

Qualification of pipe-grade HDPEs: Part I,development of a suitable accelerated ageing method

Several techniques of polymer characterization and different ageing methods have been used with the aim of developing a simple, fast and reliable method to qualify commercial pipe-grade polyethylene samples, and possibly to evidence the presence of recycled PE within PE pipes. The results of the different techniques used have been compared with respect to their capability to evidence differences in the degradation rate of different HDPE samples (including virgin HDPE, HDPE pipes obtained from virgin HDPE and HDPE pipes that probably contain recycled HDPE). FT-IR, TGA and DSC were found unsuitable for this purpose but, on the contrary, MFI measurements have been found sensitive enough to evidence different degradation rates when a suitable combination of high temperature, oxygen, mechanical stresses and mixing time had been used for ageing the sample.     

Determination of kinetic parameters and analytical pyrolysis of tobacco waste and sorghum bagasse

The thermal decomposition of tobacco waste and sorghum bagasse was investigated by non-isothermal thermogravimetric analyses, applying slow heating rates and well-defined conditions. The purpose of evaluating the decomposition was to estimate the kinetic parameters of the analyzed materials. Activation energies and Arrhenius exponential factors were inferred by different estimation methods: the classical methods of Ozawa and Starink and the independent parallel reactions model. The analytical pyrolysis was performed in a micro-pyrolyzer coupled to a gas chromatographer/mass spectrometer. Values of activation energy obtained with single step reaction models by the Ozawa method were: 103.94 kJ/mol for tobacco waste and 120.01 kJ/mol for sorghum bagasse, and by the Starink method - 135.95 kJ/mol for tobacco waste and 148.91 kJ/mol for sorghum bagasse. The independent parallel reaction model presented energy activation values of 39.7-272.0 kJ/mol for tobacco waste and 35.7-220.0 kJ/mol for sorghum bagasse. In analytical slow and fast pyrolysis of tobacco residue and sorghum bagasse, holocellulose and lignin-derived compounds were identified, as well as hydrocarbons and aromatic hydrocarbons. The kinetic behavior of the materials are presented and discussed. Our findings may be helpful in evaluating other types of lignocellulosic biomass.     

Highly Selective Catalytic Oxi-upcycling of Polyethylene to Aliphatic Dicarboxylic Acid under a Mild Hydrogen-Free Process

A low-temperature hydrogen-free process for upcycling polyethylene (PE) plastics into aliphatic dicarboxylic acid is developed using a heterogeneous catalyst Ru/TiO₂. The low-density PE (LDPE) conversion can reach 95 % in 24 h under a pressure of 1.5 MPa air at 160 °C with 85 % of the liquid product yield, which mainly is low molecular weight aliphatic dicarboxylic acid. Excellent performances can be also achieved for different PE feedstocks. This catalytic oxi-upcycling process paving a new way of upcycling polyethylene waste.