Mechanical characterization of melt spun fibers from recycled and virgin PET blends

In this study two Poly (Ethylene Terephthalate) (PET) polymers obtained from mineral water bottles and a virgin fiber grade PET polymer were investigated. In order to improve their properties when reprocessed at high temperatures, recycled polymers were blended with virgin one. Thermal and rheological properties of extruded recycled/virgin (PET-V/R) blends showed a good microstructural stability compared to extruded pure recycled polymers. Mechanical behaviour of melt spun fibers obtained from recycled/virgin blends were investigated in static (tensile) and dynamic (DMA) modes and gave interesting properties. Fatigue failure of fibers was also studied and resulting fracture morphologies were analysed by Scanning Electron microscopy (SEM).     

Dimensional stability and mechanical behaviour of wood–plastic composites based on recycled and virgin high-density polyethylene (HDPE)

This paper investigated the stability, mechanical properties, and the microstructure of wood–plastic composites, which were made using either recycled or virgin high-density polyethylene (HDPE) with wood flour (Pinus radiata) as filler. The post-consumer HDPE was collected from plastics recycling plant and sawdust was obtained from a local sawmill. Composite panels were made from recycled HDPE through hot-press moulding exhibited excellent dimensional stability as compared to that made from virgin HDPE. The tensile and flexural properties of the composites based on recycled HDPE were equivalent to those based on virgin HDPE. Adding maleated polypropylene (MAPP) by 3–5 wt% in the composite formulation significantly improved both the stability and mechanical properties. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. Dimensional stability and strength properties of the composites can be improved by increasing the polymer content or by addition of coupling agent. This project has shown that the composites treated with coupling agents will be desirable as building materials due to their improved stability and strength properties.     

Development of thermo-mechanical treatment for recycling of used concrete

Compared to virgin aggregates concrete recyclates have some specific properties because of the attached hardened cement paste. By the method of thermo-mechanical treatment, the hardened cement paste can be removed. In this paper systematic experiments are described. The aim was to understand the liberation process better. The product quality, the parameters of the process and the interaction were experimentally investigated. The results of the study show that with a low treatment temperature of 250?C300?°C and a sufficient high duration of mechanical treatment recycled aggregates with properties similar to natural aggregates can be generated.     

Analysis of the effect of mechanical recycling upon tensile strength of a short glass fibre reinforced polyamide 6,6

The effect of mechanical recycling upon tensile strength of an injection moulded polyamide 6,6 reinforced with 35% by weight of glass fibres has been experimentally investigated. Tensile tests have been conducted on specimens made of virgin material and containing different percentages of mechanically recycled material. Mechanical recycling consisted of regrinding of specimens and further injection moulding the granules into specimens of the same type. The main effect of this type of recycling is fibre breakage with consequent decrement of fibres contribution to composite strength. The results from the experimental tests have been compared with predictions obtained by applying a micro-mechanical model, which allowed taking into account the fibre length distribution and the properties of the phases of the composite. The model appeared to be a useful tool in the eco-design methodology, where the knowledge of property change of recycled material against those of the virgin one is necessary in the assessment of the environmental impacts of different recovery options.     

Effects of virgin Ethylene–Propylene–Diene–Monomer and its preheating time on the properties of natural rubber/recycled Ethylene–Propylene–Diene–Monomer blends

Blending of natural rubber/recycled Ethylene–Propylene–Diene–Monomer (NR/R-EPDM) blends was carried out. A fixed amount of carbon black and virgin Ethylene–Propylene–Diene–Monomer (EPDM) were also introduced into the blends. Applications of two different processing methods were carried out to improve the cure compatibility, crosslink distribution, and hence mechanical properties of the blends. Simple processing method was done by mixing the entire additives and rubbers on a laboratory-sized two-roll-mill at ambient temperature. Whereas, reactive processing method was conducted by mixing virgin EPDM, recycled EPDM and other compounding ingredients using an internal mixer, the compound was later preheated according to designated time before blending with natural rubber and carbon black. Results revealed that the enhancement of the physical and mechanical properties was significantly achieved towards preheating time of EPDM/R-EPDM blends. The improved properties in the blends suggested that the reactive processing method had led to more homogeneous blends due to a better crosslink distribution and more homogeneous carbon black distribution.     

Wood–plastic composites formulated with virgin and recycled ABS

It is demonstrated that wood–plastic composites (WPCs) having desirable mechanical properties can be formulated using acrylonitrile butadiene styrene (ABS) as the matrix polymer. This is accomplished by compounding the polymer with 50 wt.% wood particulates using a twin-screw extruder; both virgin resin and polymer recovered from computer monitors and keyboards were utilized for this purpose. It was found that, while the impact strength and ductility of the virgin and recycled polymers were significantly different, the composite properties differed only slightly from each other. These properties could be improved with the use of coupling agents, but the extent of improvement depended on the chemical nature of the coupling agent employed. In view of this, ABS recovered from post-consumer applications can be recycled into high-value composites without going through the expense of separating out impurities from the polymer.     

The effect of recycling on the mechanical response of carbon fibres and their composites

The development of processes for recycling carbon–fibre composite waste rises a question yet to be answered: how good can the performance of recycled composites be? This paper analyses fibres reclaimed in commercial facilities, and compares the performance of subsequently manufactured recycled woven composites to that of the virgin precursor (with the same fibre architecture). Different pyrolysis cycles resulted into different compromises between complete resin removal and full fibre strength retention. At the composite level, this paper shows how strength varies with the reclamation cycle, re-impregnation process and loading direction, while stiffness remains virtually unaffected. It is shown that composite tensile strength is favoured by gentle pyrolysis cycles generating little fibre damage, while compressive strength is fully retained after more aggressive cycles which completely remove the matrix. This work proves that the mechanical response of recycled composites can rival that of virgin precursors, while highlighting the benefits of application-driven optimisation of reclamation processes.     

From virgin to recycled bitumen: A microstructural view

In the present work, soft and hard bitumens recovered from unaged, aged and recycled asphalt concrete (AC) mixtures, which in laboratory tests performed mechanically as well as an AC mixture produced with virgin materials, were investigated regarding rheological, thermal and surface microstructural aspects. For comparison purposes, bitumen containing 50 wt% of virgin bitumen and 50 wt% of bitumen recovered from reclaimed asphalt pavement (RAP) was studied. Some properties of the bitumens remained unchanged throughout the preparation of the AC mixture, aging and recycling: Soft and hard bitumens retained their general rheological properties significantly, and their thermal and surface microstructural properties partially. Soft bitumens presented larger “bee” structures and, therefore, higher surface roughness, while hard bitumens presented smaller “bee” structures and, thus, lower surface roughness. Furthermore, soft bitumens seemed to contain higher crystalline-like content than hard bitumens. For the soft cases, the unaged recovered bitumen did not show the same characteristics (rheological and surface microstructure) as the virgin bitumen. Similarly the recovered recycled bitumen did not show the same characteristics (surface microstructure) as the bitumen prepared from the mixture of virgin bitumen and RAP bitumen. Aging of the AC mixture changed the rheological properties of the soft bitumen by increasing the complex modulus and decreasing the phase angle. Similarly, recycling changed the rheological properties by increasing the complex modulus and decreasing the phase angle. Compositional changes occurred during AC mixture preparation (possibly also aging and recycling) for both soft and hard bitumens. Consequently, more “phases” were observed on the surface microstructure for the recovered bitumens as compared with the virgin bitumens. However, no significant trend was found for the surface microstructure characteristics between the unaged, aged and recycled recovered bitumens. Moreover, the nature of the virgin bitumen influenced the properties of the recycled recovered bitumen, e.g. the glass transition temperature.     

Processing of hybrid wood plastic composite reinforced with short PET fibers

Poly(ethylene terephthalate) (PET) fibers (virgin, waste, and mixed) were incorporated in the composite poly(methyl methacrylate) (PMMA)–wood. Hybrid composite panels were prepared by pressure molding. Toluene-2,4-diisocyanate (TDI) and (3-mercaptopropyl)trimethoxysilane (MPTMS) were used as cross-linking bonding agents for modification of wood fibers. Influence of cross-linking bonding agents, structure, and composition of PET fibers was examined by studying thermomechanical properties as well as moisture absorption. Moisture absorption was lower for composites with bonding agents. Mechanical testing revealed that the addition of PET fibers drastically enhances properties of the composites. Covalent and hydrogen bonds formed with the addition of bonding agents have also improved mechanical properties compared to the untreated composites.     

The effect of recycling on the oxygen distribution in Ti-6Al-4V powder for additive manufacturing

Abstract

Ti-6Al-4V powder has been recycled 30 times in an electron beam melting system. A combination of electron microscopy techniques has been used to show that the recycled powder has a 35% higher oxygen content, and that the particles have a more irregular morphology, a narrower particle size distribution, and a much more variable microstructure than the virgin powder. The microstructures in the recycled powder particles vary from a martensitic α′ structure, which is identical to that in the virgin powder, to a two-phase α + β structure. This variability is related to the complex thermal history of the unmelted metal powder in the system. Despite these differences, all of the particles exhibit essentially the same surface oxide thickness; the excess oxygen in the recycled powders is instead located in the β phase. The possible consequences for the structure and properties of the resultant additively manufactured parts are discussed.     

Experimental study of the thermo-mechanical properties of recycled PET fiber-reinforced concrete

This work presents an experimental study of thermal conductivity, compressive strength, first crack strength and ductility indices of recycled PET fiber-reinforced concrete (RPETFRC). We examine PET filaments industrially extruded from recycled PET bottle flakes with different mechanical properties and profiles. On considering a volumetric fiber dosage at 1%, we observe marked improvements in thermal resistance, mechanical strengths and ductility of RPETFRC, as compared to plain concrete. A comparative study with earlier literature results indicates that RPETFRC is also highly competitive over polypropylene-fiber-reinforced concrete in terms of compressive strength and fracture toughness.     

Fibrillar polymer–polymer composites: morphology, properties and applications

Micro- or nano-fibrillar composites (MFCs or NFCs) are created by blending two homopolymers (virgin or recycled) with different melting temperatures such as polyethylene (PE) and poly(ethylene terephthalate) (PET), and processing the blend under certain thermo-mechanical conditions to create in situ fibrils of the polymer that has the higher-melting temperature. These resulting fibrillar composites have been reported to possess excellent mechanical properties and can have wide ranging applications with suitable processing under controlled conditions. However, the properties and applications very much depend on the morphology of created polymer fibrils and their thermal stability. The present paper develops an understanding of the mechanism of micro-/nano-fibril formation in PE/PET and polypropylene (PP)/PET blends by studying their morphology at various stages of extrusion and drawing. It is revealed that this subsequent mechanical processing stretches the polymer chains and creates fibrils of very high aspect ratios, thus resulting in superior mechanical performance of the composites compared to the raw blends. The study also identifies the primary mechanical properties of the main types of MFCs, as well as quantifying their enhanced resistance to oxygen permeability. Furthermore, the failure phenomena of these composites are studied via application of the modified Tsai–Hill criterion. In addition to their usage as input materials in different manufacturing processes, possible applications of these fibrillar composites in two different areas are also discussed, namely food packaging with controlled oxygen barrier properties and biomedical tissue scaffolding. Results indicate a significant scope for using these materials in both areas.     

Mechanical studies of single glass fibres recycled from hydrolysis process using sub-critical water

The study reports mechanical performance of the recycled glass fibres produced from a water-based solvolysis technology, known as the hydrolysis process. The chemical reaction was carried out using sub-critical water to dissolve polyester resin and recover the glass fibres from composites. The effect of temperatures, times, catalyst and water amount on mechanical properties of the recovered glass fibres were investigated. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and time-of flight secondary ion mass spectroscopy (ToF-SIMS) analyses were also employed to examine the fibre surface associated with the polyester resin eliminated level after the hydrolysis reaction. The results revealed that by carefully adjusting the hydrolysis parameters the tensile strength and failure strain of the recycled fibres decrease by approximately 40-70% in comparison with virgin fibres while Young’s moduli remain similar. The relationship between the hydrolysis conditions, recovered fibres and mechanical performance was discussed in this study.     

Recycled carbon fibre for high performance energy absorption

This paper compares the mechanical properties of virgin and recycled woven carbon fibre prepreg and goes on to assess the potential for recycled carbon fibre reinforced plastic (rCFRP) to be used in high performance energy absorption structures. Three sets of material were examined: fresh containing virgin fibres and resin, aged which was an out of life but otherwise identical roll and recycled which contained recycled fibre and new resin. The compressive strength and modulus of rCFRP were approximately 94% of the values for fresh material. This correlated directly with the results from impact testing where rCFRP conical impact structures were found to have a specific energy absorption of 32.7 kJ/kg versus 34.8 kJ/kg for fresh material. The tensile and flexural strength of rCFRP were 65% of the value for fresh material. Tensile and flexural moduli of rCFRP were within 90% of fresh material and ILSS of rCFRP was 75% that of fresh.     

多因素对再生混凝土力学性能及抗冻性的影响

为研究不同因素、不同水平对再生混凝土力学性能的作用。该文通过正交试验研究钢纤维掺量、再生粗骨料掺量和粉煤灰掺量对再生混凝土力学性能(抗压强度、劈裂抗拉强度和抗折强度)的影响,确定各因素对再生混凝土力学性能的影响程度,并加以量化表征,并提出多因素共同作用下再生混凝土力学性能的多元非线性回归模型且进行验证。在此基础上,该文进一步研究再生混凝土的抗冻性。结果表明:再生混凝土的力学性能随钢纤维掺量的增加而提高;随粉煤灰掺量增加而降低;再生粗骨料掺量对再生混凝土的力学性能影响较小。钢纤维的掺入可提高再生粗骨料的掺量。再生混凝土力学性能的实测值与通过建立的回归模型得到的计算值的最大误差在6.5%以内。此外,钢纤维的掺入和减少再生粗骨料的掺量均可以提高再生混凝土的抗冻性。     

Evaluation of oriented poly(lactide) polymers vs. existing PET and oriented PS for fresh food service containers

Poly(lactide) (PLA) polymers have garnered increasing attention in the last few years as food packaging materials because they can be obtained from renewable resources; their production consumes quantities of carbon dioxide; they can be recycled and composted; and their physical and mechanical properties can be tailored through polymer architecture. As a consequence, PLA is becoming a growing alternative as a ‘green’ food packaging material. PLA's optical, physical and mechanical properties have been compared to those of polystyrene (PS) and polyethylene terephthalate (PET), although studies comparing and showing the actual performance of PLA, PS and PET plastics containers are scarce. The purpose of this study was to investigate and compare the role of PLA in package sustainability for the food service industry. Two of the commonly used materials to make containers to package fresh food, PET and oriented polystyrene (OPS), were compared with oriented PLA (OPLA) and OPLA with 40% recycled content from the industrial trimming process. The recycled OPLA provides an opportunity for full material utilization and lower costs. This study involved a number of tests to quantify the physical, mechanical, barrier and compatibility properties that would affect the selection criteria for containers to be used for food service applications. Based on the data collected, OPLA, OPLA + 40% regrind, OPS and PET performances were evaluated. Exposure of the four materials to vegetable oil and weak and strong acids show a minimal reduction in the performance of these polymers. At ambient temperature, PET has the highest impact resistance, followed by OPLA, OPS and OPLA + 40% regrind. In terms of barrier properties, PET shows the highest oxygen barrier, followed by OPLA, OPLA 40% recycled content, and OPS. Thus, OPLA and OPLA with 40% recycled content can be used for fresh food applications as well as OPS and PET, and in many situations it performs better than OPS and PET. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of gamma irradiation on polypropylene, polypropylene + high density polyethylene and polypropylene + high density polyethylene + wood flour

The effect of the gamma-irradiation on the mechanical properties of the composites, Polypropylene (PP), PP+high density Polyethylene (HDPE), PP+ HDPE+wood flour, where HDPE is virgin and recycled, was studied. This paper discusses the behavior of the composites after exposure to various doses of gamma irradiation (1–7 MRads) in the presence of oxygen. The dependence of mechanical properties on the integral dose for a constant dose rate of 0.48 MRads/h confirms the influence of the irradiation. Strong effects on the elongation at break and break strength is noticed. The mathematical analysis suggests for the PP+r-HDPE a bimolecular process of the elongation at break. On the order hand, for the PP+HDPE a complex process is represented for a three exponential equation. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

Dissipative Behaviour Analysis of Reprocessed Polyethylene Terephthalate using Digital Image Correlation and Updated Finite Element Analysis

Abstract: Polyethylene terephthalate (PET) is a semi‐crystalline polyester that is usually processed by conventional methods. However, the degradation of this polyester during the melting process impacts its macroscopic behaviour, which is particularly true for recycled PET that is subjected to multiple processes at the melting temperature by extrusion, injection‐moulding or pelletizing. In this work, the impact of reprocessing on the mechanical properties of PET is studied. This approach requires exploring the influence of implementation on both its own mechanical performance factor and on the damage linked to the striction problem. An experimental protocol was developed to study large strain responses through a set of sequenced and instrumented uniaxial traction tests based on the standard ISO‐5272‐1‐A and hourglass geometries. Updated finite element simulations were coupled with digital image correlation, thereby providing access to the parameters of a phenomenological model. This coupled approach enables researchers to understand both the complex shape of the stress–strain curve and the well‐known dilatant mechanism that is observed during uniaxial deformation.     

Improvement of mechanical properties of recycled plastic blends via optimizing processing parameters using the Taguchi method and principal component analysis

In this paper, the Taguchi method and principal component analysis (PCA) are used to improve the mechanical properties of recycled polypropylene (PP) blends in injection moulding procedure, with detailed assessments performed on each method and comparison was made based on results of both the methods. The experimental design was carried out by adopting a L9-3⁴ Taguchi orthodoxy array (OA), which has four controllable factors (i.e., melt temperature, mould temperature, injection speed and packing pressure) at three levels. Injection moulded specimens made from different compositions of virgin-recycled PP were tested to determine the optimal conditions for the injection moulding procedure. The effects of the processing parameters and the proportion of recycled plastic in composites on the mechanical properties were investigated, the optimal conditions for desired properties were obtained and then verified. The appropriate blending ratio of virgin and recycled plastic was evaluated. The results reveal that deteriorations in the mechanical properties of products produced from recycled plastic can be improved by optimizing the processing parameters during the injection moulding procedure.     

Effect of recycled content and rPET quality on the properties of PET bottles,part I: Optical and mechanical properties

The effect of recycled content and type of recycled poly (ethylene terephthalate) (rPET) on the haziness; colour parameters L*, a*, and b*; total colour change; ultraviolet-visual spectrum (UV-VIS) absorption; and environmental stress cracking (ESC) of PET bottles was studied. Three series of PET bottles were made at a small scale production facility with same type of virgin PET and three different types of rPET with recycled contents of 25%, 50%, 75%, and 100%. Also, the particle contamination of the produced PET bottles was studied by dissolving bottle fragments and counting the insoluble particles. A linear relationship was found between the haziness of PET bottles and the particle contamination, with a coefficient of determination of 0.96. Linear relationships were also found between the colour parameters L* and b* and the particle contamination of the PET bottles, but the slope differed for each type of rPET. The origin of rPET (mono-collection or cocollection) seems to be the crucial factor determining particle contamination and colour of the produced bottles. No correlation was found between the recycled content and the incidence of ESC. However, PET bottles in which high intrinsic viscosity (IV) values were measured showed lower chances of ESC than PET bottles with low IV values