Properties and treatments of pulps from recycled paper. Part II. Surface properties and crystallinity of fibers and fines

Surface properties of bleached kraft pulps were evaluated before and after recycling, and after a series of chemical treatments designed to improve and/or modify the pulp characteristics. The surface free energy characteristics of the pulps were determined using the Wilhelmy technique, and ESCA and ATR-FTIR methods were used to evaluate the chemical composition of the surfaces of the pulp fibers. In general rather small changes were noted at the fiber surfaces with recycling and chemical treatment. Recycling tended to increase the acid component and decrease the base component of the surface free energy of the pulps. This could result from exposure of carboxyl groups from hemicelluloses and/or from oxidized layers from the bleaching process. ESCA analyses also indicated increased carboxyl concentration at the surfaces of the recycled fibers. Although treatment with aqueous bases and organic solvents tended to increase the hydroxyl content on the surface of recycled pulps, the chemical treatments were not beneficial to pulp quality. AFM and SEM of fiber and fine surfaces of kraft pulps revealed that the fines fraction was altered to a much greater extent with recycling. Although recycled fibers appeared to have improved wettability, these small changes in the surface characteristics do not appear to play the dominant role in the characteristics of recycled pulps. Recycling did not change the crystallinity of whole pulps, but it increased the crystallinity of the fines fraction. The increase in the crystallinity of the fines fraction and the reduction in the water retention value (WRV) and the bulk carboxyl content (xylan) of the recycled pulps, as noted in Part I of this paper, appear to play the predominant role in determining the characteristics of recycled pulps. It appears that the loss of the hemicelluloses in the bulk of the fiber with recycling is much more important for internal fibrillation than the apparent small increase of hemicelluloses at the surface of recycled fibers.     

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.     

Temperature and variable strain rate sensitivity in recycled HDPE

The recycling of post-consumer plastics and their utilization as raw materials to develop value-added products has become an important goal worldwide. The present work is concerned with the thermo-mechanical analysis of recycled high-density polyethylene (HDPE) under uniaxial tensile loading. The main focus is to propose a one-dimensional phenomenological model able to describe the influence of temperature and strain rate on the mechanical behavior. Tensile tests were performed over a wide range of temperatures (from 25°C to 100°C). Each experiment was performed under controlled strain rate varying from 7.25 × 10⁻⁵ s⁻¹ to 7.25 × 10⁻³ s⁻¹ in steps. It is shown that only one tensile test performed at three different temperatures is necessary to fully identify experimentally all material parameters that arise in the theory. Thus, with this experimental procedure, the number of tests used to evaluate the mechanical properties of recycled HDPE is significantly reduced. The experiments are compared with the model predictions and show good agreement.     

Void formation due to gas evolution during the recycling of Acrylonitrile-Butadiene-Styrene copolymer (ABS) from waste electrical and electronic equipment (WEEE)

During processing of recycled ABS and ABS/HIPS blends, voiding defects can occur within the resulting material which can result in deterioration of mechanical properties. The voids were previously thought to be caused by the evolution of volatile substances during processing. This study investigated the recycling of post-consumer ABS from a variety of types of WEEE. The mechanical properties of the processed material were assessed and a combination of visual observation during processing and optical microscopy was used to identify the extent of voiding. It was found that flexural strength and ductility in particular decreased with increased levels of voids. The gases emitted during heating and processing were analysed using Gas Chromatography with Mass Spectroscopy (GCMS) and were found to be breakdown products of the original polymers. These seem to be present in the WEEE, either as polymerization residuals or as products of degradation during the initial service life rather than degradation products from reprocessing. The amounts of volatiles liberated were quantified, which showed that the volatile emissions from post-consumer material were of a similar magnitude to those seen with virgin material. More intensive or longer processing led to a reduction in the emissions and voiding and an improvement in strength, suggesting that there is a finite potential for volatile liberation, and that the problem could be overcome by the use of suitable processing conditions.     

Characterisation of filled and recycled PA6

Filled PA6 are important representatives of engineering plastics used in automotive components. Nowadays, the demand of plastic recycled grades is increasing in this branch of industry but polymer recycling can undergo thermomechanical degradation processes with the results of a poor secondary material, regarding its properties. In this paper an investigation of thermal, mechanical (tensile, flexural and impact tests) and rheological properties of a sample of recycled and filled PA6, is reported as a function of the number of reprocessing operations (3 times) and of the fraction of recycled material (15, 30 and 50%) added to the virgin material. Recycled PA6, used in this study, comes from fibre grade production waste. Material was filled with 20% glass beads and 10% glass fibre, according to the specifications of the application, mainly to obtain a lower shrinkage in the end product. This work also shows that the mineral fraction, not being degraded during the injection process, allows better recyclability to the filled material. The properties of the recycled material remain below the virgin, and the best combination of both appears to be the mixture with 30w.% recycled fraction, which shows a lost of properties similar to 3 reprocessing operations.     

Mechanical properties of recycled polymers

Modifications of structure and morphology of the polymers induced by the thermomechanical stress (or by the presence of water for some polymers) during reprocessing can cause a drastic deterioration of mechanical properties of the recycled material. The property - reprocessing relationships are an important tool to determine not only the properties of the recycled polymers but also the strategies to use (processing conditions, stabilizers, fillers, compatibilizers, etc) in order to obtain recycled polymers with good mechanical properties. In this work, typical behaviour of some mechanical properties as a function of the number of reprocessing operations is discussed and correlated with their structure and morphology. The influences of the type of apparatus and of the processing conditions are also considered.     

Simultaneous measurement of mechanical and surface properties in thermoresponsive, anchored hydrogel films

Hydrogel films have been used extensively in the preparation of biosensors and biomedical devices. The characteristics of the aqueous interface of the polymer layer are significant for the biosensor or device function; likewise, the changing mechanical properties of thermoresponsive polymers are an important feature that affects the polymer behavior. Atomic force microscopy was used here to characterize both the surface and the mechanical properties of polymeric hydrogel films prepared from a thermoresponsive terpolymer of N-isopropylacrylamide and acrylic acid with benzophenonemethacrylate as a photoreactive cross-linker comonomer. The force-distance curves thus obtained were analyzed to assess both the surface forces and the mechanical response that were associated with the hydrogel. These properties were investigated as a function of temperature, in water and in Tris buffer, for different degrees of polymer cross-linking. For samples in water, the distance over which the surface forces were effective was found to remain constant as the temperature was increased from 26 to 42 °C, even though the mechanical response indicated that the samples had been heated past the lower critical solution temperature, or LCST. The bulk of the polymer becomes less soluble above the LCST, although this does not seem to affect the surface properties. This may be due to the segregation of the acrylic acid-rich polymer segments near the gel surface, which is in agreement with reports for related systems.     

Properties and treatments of pulps from recycled paper. Part I. Physical and chemical properties of pulps

The mechanical, physical, and chemical properties of recycled pulps were evaluated after a series of treatments designed to improve and/or modify the pulp characteristics. Tensile strength, bursting strength, and apparent density of the pulps decreased with recycling. However, the tear strength, in most cases, increased after the first recycle and then decreased after the second recycle. Carboxyl content and WRV of pulps also decreased with recycling. Chemical treatments did not increase the bonding ability of recycled pulps and, in most cases, decreased the physical properties of the pulps. Altering the physical state of the cellulose microstructure through additional swelling did not appear to be a significant factor for strength restoration. It may be that the hemicelluloses plan a greater role in recycling than originally thought.     

The prediction of mechanical properties of injection moulding parts by vacuum casting

The behaviour of vacuum cast prototypes and injection moulding parts in mechanical tests was compared. The mechanical tests were made using real production parts as references. Distinct correlations were found between vacuum cast prototypes and injection moulding parts. In this light, vacuum cast prototypes can be used for the evaluation of injection moulding products with certain limitations. Vacuum casting is best suited for the evaluation of such mechanical properties of injection moulding products as tensile, flexural and compression strength, while impact strength is the property that is most difficult to evaluate.     

Mechanical properties and molecular structures of virgin and recycled HDPE polymers used in gravity sewer systems

The widespread use of plastics in the conditioning, packaging and building material sectors generates an enormous amount of industrial waste which could be recycled for wastewater pipes and fittings. Nevertheless, current manufacturing standards in the piping industry recommend against the use of post-consumer recycled materials—a policy based on inadequate understanding of the properties and long-term mechanical performance of recycled materials. The present study compared the material characteristics of virgin and recycled high-density polyethylene (HDPE) plastics commonly found in the piping industry. Mechanical testing, oxidative induction time (OIT), melt flow index (MFI) and thermal analysis were used in conjunction with X-ray fluorescence (μ-XRF), size exclusion chromatography and ¹³C solid-state NMR to evaluate mechanical behavior and molecular structure as well as contaminant or filler contents. This study provides evidence for the degradation processes impact that can occur when post-industrial and post-consumer polymers are recycled. However, the study identified two measures to improve the material qualities of post-consumer recycled HDPE: 1) reducing the amount of contaminants or, alternatively, improving their compatibility with HDPE resins, and 2) improving current sorting and recycling processes to increase the amount of tie molecules in HDPE materials.     

Étude des propriétés des mélanges pebd régénéré / pebd vierge

This study is a contribution to the valorization of recycled low-density polyéthyléne (LDPE). First the characterization of five recycled LDPE produced from wastes coming from different sources was performed. The physical properties (density, melt flow index), chemical structure (Fourier transform infra-red spectroscopy) and mechanical properties (tensile strength and hardness) were investigated. The effect of the ratio of virgin LDPE on these physical and mechanical properties was studied in the case of the blends of recycled LDPE / virgin LDPE.     

Modification of Recycled Polymer Blends with Activated Natural Zeolite

The growing interest in the natural zeolite is based on some specific peculiarities of its structure, which after dehydration enables adsorption processes of some polymer molecules and/or segments to take place on the zeolite surface. The main goal of the study is to investigate the effect of dehydrated zeolite on the flow behavior, mechanical properties and morphology of immiscible blends from unsorted polymer wastes. A tetra-component blend consisting of 40 wt.% polypropylene (PP), 40 wt.% high-density polyethylene (HDPE), 15 wt.% low-density polyethylene (LDPE) and 5 wt.% polystyrene (PS), was studied as a model system of commingled plastic wastes. Compositions from recycled blend and dehydrated zeolite in a wide concentration range (from 0 to 20 wt.%) were prepared using a twin-screw extruder Brabender DSE 35/17D in the temperature range from 140 to 190 °C. The compositions were characterized by capillary rheometry, differential scanning calorimetry (DSC), site-resolved wide-angle X-ray scattering (WAXS) and mechanical tests. The results show a compatibilizing effect of dehydrated zeolite at low concentration levels (1-2 wt.%) and open wide possibilities for utilization of dehydrated zeolite in the recycling of unsorted polymer wastes.     

包覆重钙粉为填充剂的橡胶加工及性能

重钙粉作为填充剂被广泛应用于橡胶加工过程,但由于其表面具有极性,分散性较差,导致与橡胶材料界面结合较差,影响了橡胶产品的抗拉强度、断裂伸长率等力学性能。 本文采用沉淀法,在CaCl₂-H₂O-NH₃-CO₂体系中生成碳酸钙直接结晶于重钙粉颗粒表面,实现对重钙粉的表面包覆,将n(CaCl₂)：n(重钙粉)=1：100、5：100、10：100的包覆重钙粉填充到天然橡胶和再生胶中,橡胶的力学性能与填充未包覆重钙粉的橡胶相比有了一定的提升。 通过比较,在填充量较大(8.5%、15%)时,包覆重钙粉橡胶产品在硬度、定伸应力等力学性能上要好于轻钙粉橡胶产品;在填充量(5%、8.5%)时,包覆重钙粉橡胶产品的抗拉强度、断裂伸长率接近于白炭黑,硬度高于白炭黑橡胶产品。     

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

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

Degradation behavior and application of recycled PVC sheet made of floor sheet for railway vehicle

A floor sheet made of plasticized poly(vinyl chloride) (PVC) is used as interior material for railway vehicle. Some of the floor sheets mainly used in Express and Shinkansen vehicles were layered by vulcanized surface to protect against the fire. Therefore, these floor sheets have been considered as inappropriate material for recycling. In this paper, some varieties of recycled sheets made of these floor sheets have been studied with respect to a long-term stability which is necessary for practical application. Through the weathering test, these recycled sheets indicated suitable mechanical properties for long-term outdoor use; however, at the beginning of weathering test, the elongation was reduced by the rapid flow out of plasticizer. The mechanical strength was closely related to the plasticizer concentration. Based on the plasticizer concentration, the tensile strength could be estimated without dependence of specimen preparations and the slope of the elongation was related to the content of the floor sheet. To prevent flowing out of plasticizer, virgin PVC was laminated to the surface of recycled sheet. The laminated sheet was set up at the outdoor to be used as an anti-weed sheet. For more than five years, the laminated sheet has kept on preventing overgrowth of weed and flow out speed of plasticizer has decreased by the effect of virgin PVC lamination. It is presumable that the laminated sheet was estimated to be used as the anti-weed sheet for more years.     

Analytical strategies for the quality assessment of recycled high-impact polystyrene: a combination of thermal analysis, vibrational spectroscopy, and chromatography

Various analytical techniques (thermal analysis, vibrational spectroscopy, and chromatographic analysis) were used in order to monitor the changes in polymeric properties of recycled high-impact polystyrene (HIPS) throughout mechanical recycling processes. Three key quality properties were defined and analysed; these were the degree of mixing (composition), the degree of degradation, and the presence of low molecular weight compounds. Polymeric contaminations of polyethylene (PE) and polypropylene (PP) were detected in some samples using differential scanning calorimetry (DSC). Vibrational spectroscopy showed the presence of oxidised parts of the polymeric chain and gave also an assessment of the microstructure of the polybutadiene phase in HIPS. The presence of low molecular weight compounds in the HIPS samples was demonstrated using microwave-assisted extraction followed by gas chromatography-mass spectrometry (GC-MS). Several volatile organic compounds (VOCs), residues from the polymerisation, additives, and contaminations were detected in the polymeric materials. Styrene was identified already in virgin HIPS; in addition, benzaldehyde, α-methylbenzenaldehyde, and acetophenone were detected in recycled HIPS. The presence of oxygenated derivates of styrene may be attributed to the oxidation of polystyrene (PS). Several styrene dimers were found in virgin and recycled HIPS; these are produced during polymerisation of styrene and retained in the polymeric matrix as polymerisation residues. The amount of these dimers was highest in virgin HIPS, which indicated that emission of these compounds may have occurred during the first life-time of the products. This paper demonstrates that a combination of different analytical strategies is necessary to obtain a detailed understanding of the quality of recycled HIPS.     

Effect of molecular interactions on the miscibility and structure of polymer blends

The effect of polymer-polymer interactions on the miscibility and macroscopic properties of PVC/PMMA, PVC/PS and PMMA/PS blends were studied in the entire composition range. The miscibility of the components was characterized by the Flory-Huggins interaction parameter or by quantities related to it. Thermal analysis, light transmittance measurements, and scanning electron microscopy were carried out on the blends and their mechanical properties were characterized by tensile tests. Interactions were analyzed by infrared spectroscopy and contact angle measurements. All three polymer pairs form heterogeneous blends, but the strength of molecular interactions is different in them, the highest is in PVC/PMMA system resulting in partial miscibility of the components and beneficial mechanical properties. The structure of these blends depends strongly on composition. A phase inversion can be observed between 0.5 and 0.6 PMMA content accompanied with a significant change in structure and properties. The PVC/PS and the PMMA/PS pairs are immiscible, though the results indicate the partial solubility of the components. The analysis of the surface characteristics of the components and the comparison of quantities derived from them with miscibility as well as with the macroscopic properties of blends revealed that blend properties cannot be predicted in this way, since they are affected by several factors.     

Study and characterization of virgin and recycled LDPE/PP blends

Recycling of mixed plastic wastes composed of low-density polyethylene (LDPE) matrix and polypropylene (PP) was carried out by compounding using single-screw or twin-screw extruders. Blends of virgin polymers have been prepared to compare mechanical properties of both virgin and regenerated materials. First, a model composition of virgin LDPE/PP blend was prepared to study the effect of process parameters and that of different types of compatibilizers. Second, the results were applied to plastic wastes coming from industrial post-consumer plastic wastes. By adding compatibilizing agents such as ethylene-propylene-diene monomer, ethylene-propylene monomer, or PE-g-(2-methyl-1,3-butadiene) graft copolymer, elongation at break and impact strength were improved for all blends. The effect of these various copolymers is quite different and is in relation with their chemical structure. The recycled blends exhibit suitable properties leading to applications that require good mechanical properties.     

Processing and properties of engineering plastics recycled from waste electrical and electronic equipment (WEEE)

The characteristics of engineering plastics used in the preparation of electrical and electronic equipment were studied. More specifically, their thermal response was recorded by DSC experiments, the rheological properties were investigated via MFI tests and the mechanical properties were evaluated with tensile tests. The aim was to establish a procedure for recycling the same engineering plastics deriving from waste of electrical and electronic equipment (WEEE), which offers the additional advantage of using the as-received waste stream as a recyclable mixture, i.e. without sorting and classification of its components.The experimental results showed that blends of PC with ABS or ABS/HIPS can be prepared by direct mixing and this, would allow easy handling of the engineering plastics coming from WEEE, i.e. blending without the need of sorting. These mixtures can be easily processed and display acceptable mechanical properties with reasonable cost. Therefore, the processing characteristics and properties of the systems studied in this work could be the key for the design of an interesting approach for handling solid plastic waste from electrical and electronic devices.     

Comparison of the Characteristics of Recycled Carbon Fibers/Polymer Composites by Different Recycling Techniques

In this study, three recycling methods, namely, mechanical grinding, steam pyrolysis, and the supercritical solvent process, which are used to acquire recycled carbon fibers (RCFs), were compared for their application in synthesizing polymer-matrix composites. RCF-reinforced polyethylene (PE) composites were prepared to compare the mechanical properties of the composites generated using the three recycling methods. The PE/RCF composites exhibited 1.5 times higher mechanical strength than the RCF-reinforced PE composites, probably because of the surface oxidation effects during the recycling processes that consequently enhanced interfacial forces between the RCF and the matrix. Further, the steam pyrolysis process showed the highest energy efficiency and can thus be applied on a large production scale in domestic recycled CF markets.