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.     

Percolation simulation of the network degradation during ultrasonic devulcanization

The percolation model of network degradation during rubber devulcanization is presented. The model is based on a random crosslink scission and molecular chain breakup. The obtained results indicate that the primary model parameter characterizing the network degradation is the ratio of the probabilities of backbone breakup to crosslink scission. The predicted dependences of the gel fraction of devulcanized rubber on crosslink density are in excellent agreement with experimental data for styrene-butadiene rubber and ground rubber tire. The estimated critical exponents indicate that the process of devulcanization for the vulcanizate without filler appears to belong to the universality class of standard 3D bond percolation while devulcanization for the vulcanizate with filler appears to belong to its own new universality class. © 1996 John Wiley & Sons, Inc.     

润滑油对轮胎主要成分催化裂解行为的影响

本文研究了润滑油对轮胎的重要组成原料:天然橡胶、聚丁二烯橡胶和丁苯橡胶催化裂解行为的影响.研究发现润滑油的加入明显增强了催化剂ZSM-5对聚丁二烯橡胶的催化裂解作用:液体收率从69.0％提高到83.4％,残渣收率从17.0％降至3.2％;润滑油的加入也提高了丁苯橡胶催化裂解的反应速率,液体产物中的轻油组分由67.5％增...     

Structure-propery relationship of low molecular weight ‘liquid’ polymers in blends of sulfur cured SSBR-rich compounds

In recent years, many patents have been published that are claiming the use of low molecular weight ‘liquid’ polymers in tire tread applications. Herein, tire producers generally introduce improved balances of the tire performances such as wet grip, abrasion resistance and rolling resistance. To understand the influence of the low molecular weight ‘liquid’ polymers in detail, an investigation was carried out to create more clarity about the influence of the structure of these polymers on in-rubber properties and about their interaction with the base polymers and fillers. One basic formulation was selected: A silica filled compound with styrene butadiene copolymer (SSBR), polybutadiene (BR) and natural rubber (NR) that is representing a winter tire tread formulation. Different structures of the low molecular weight ‘liquid’ polymer were added to this compound and compared. Results are discussed for the curing torques and crosslink densities to evaluate the influence on the crosslinking. Payne effect and bound rubber content was measured to evaluate the filler-filler interactions and filler-polymer interactions, respectively. The mechanical properties and dynamic mechanical analysis results deliver finally indications for the expected tire performance.     

Styrene/butadiene copolymer synthesized by reactive extrusion

In this study,we present a method to synthesize styrene-butadiene copolymer,using anionic polymerization in a co-rotating closely intermeshing twin-screw extruder.The weight content of polybutadiene in these copolymers was above 50% although in the past studies it had been possible to accomplish levels higher than 30%.1H-NMR and GPC show that the molecular structure of the two polymers is different due to different feeding method.In terms of the structure of the polymerized products,the mechanism of polymerization in the bulk polymerization is discussed.TEM and DMA show that two phases in the block copolymer are completely incompatible,leading to sharp phase separation,while the case is complicated in the copolymer through the mixture feeding.Traditionally,styrene-butadiene rubber is mainly synthesized by solution polymerization.Reactive extrusion in this paper provides a possibility to synthesize these products in an environmentally friendly way.     

Chromatographic pattern in recycled high-impact polystyrene (HIPS) - Occurrence of low molecular weight compounds during the life cycle

The analysis of the chromatographic pattern of virgin, reprocessed, thermo-oxidised, and recycled high-impact polystyrene (HIPS) proves to be a suitable and sensitive tool to assess the degree of degradation of HIPS during its first life and subsequent recycling. Different low molecular weight compounds, such as residues of polymerisation, degradation products, and additives have been identified and relatively quantified in HIPS, using microwave-assisted extraction and further analysis by gas chromatography-mass spectrometry (GC-MS). The release of residues of polymerisation has been proven to occur during reprocessing, thermo-oxidation, and in recycled samples, which may show the emissions of volatile and semi-volatile organic compounds during the life cycle of HIPS. A wide range of oxidised degradation products are formed during reprocessing and thermo-oxidation; these products can be identified as oxidised fragments of polystyrene (PS), oxidised fragments from polybutadiene (PB) phase, and oxidised fragments from the grafting points between the PS and PB phase. Real recycled HIPS samples may also contain contaminations and fragments from additives included in their original formulations; the presence of brominated fragments from flame retardants in electronic waste is here observed.     

Reactive Compatibilization of Polyethylene/Ground Tire Rubber Inhomogeneous Blends via Interactions of Pre-Functionalized Polymers in Interface

Summary: Reactive compatibilization of recycled low- or high-density polyethylenes (LDPE and HDPE, respectively) and ground tire rubber (GTR) via chemical interactions of pre-functionalized components in their blend interface has been carried out. Polyethylene component was functionalized with maleic anhydride (MAH) as well as the rubber component was modified via functionalization with MAH or acrylamide (AAm) using chemically or irradiation (γ-rays) induced grafting techniques. The grafting degree and molecular mass distribution of the functionalized polymers have been measured via FTIR and Size Exclusion Chromatography (SEC) analyses, respectively. Thermoplastic elastomer (TPE) materials based on synthesized reactive polyethylenes and GTR as well as ethylene-propylene-diene rubber, EPDM were prepared by dynamic vulcanization of the rubber phase inside thermoplastic (polyethylene) matrix and their phase structure, and main properties have been studied using DSC and mechanical testing. As a final result, the high performance TPE with improved mechanical properties have been developed.     

The Effect of multi-reprocessing on the structure and characteristics of thermoplastic elastomers based on recycled polymers

The effect of multi-reprocessing on the phase structure and characteristics is studied for thermoplastic elastomers based on recycled high-density polyethylene (HDPE), ethylene-propylene-diene rubber (ternary copolymer of ethylene, propylene, and 5-ethylidene-2-norbornene) (EPDM), and recycled ground tire rubber (RGTR). Analysis of the viscous flow characteristics of thermoplastic elastomers shows that, independently of the number of processing cycles, all samples are characterized by the required flow characteristics at elevated temperatures. Processing of thermoplastic elastomers is accompanied by the competing processes of crosslinking and degradation of macromolecules in a polymer mixture. The results of DSC study and dynamic mechanical thermal analysis show that, as the number of processing cycles is increased, phase separation between amorphous and crystalline phases in thermoplastic elastomers decreases. Insignificant intermolecular crosslinking induced by the processing of thermoplastic elastomers appears to have almost no effect on the physicomechanical characteristics of the final material.     

Reactive compatibilization of recycled low density polyethylene/butadiene rubber blends during dynamic vulcanization

For reactive compatibilization of the recycled LDPE with butadiene rubber (BR) an equal quantity of few couples of reactive polyethylene copolymer/reactive polybutadiene (1/1) were introduced into the corresponding phases before the dynamic vulcanization. The LDPE/BR thermoplastic dynamic vulcanizates (TDVs) produced using the poly(ethylene-co-acrylic acid), PE-AA/polybutadiene terminated with isocyanate groups, PB-NCO compatibilizing couple with different ratio of functional groups have demonstrated the best mechanical properties and have been characterized by X-Ray analysis and DMTA measurements. For all of systems studied the increasing components compatibility due to the formation of the essential interface layer have been observed. The PB-NCO modifier participates in two processes: it is co-vulcanised with BR in rubber phase and reacts in the interface with the PE-AA dissolved in LDPE. The amorphous phase of LDPE is dissolved by rubber phase, i.e. the morphology with dual phase continuity is formed that provides an improvement of mechanical characteristics of material obtained. The best combination of mechanical characteristics was obtained for LDPE(PE-AA)/BR(PB-NCO), PB-NCO=7.5 wt.% per PB, COOH/NCO=1/1. The tensile strength and an elongation at break for these blends were 3.9 MPa and 353% and for the basic non-compatibilized blend 3.2 MPa and 217%, relatively.     

Ion-Free latex films as dual-phase electrolytes: Styrene–butadiene rubber and nitrile–butadiene rubber synthesized by emulsion polymerization with poly-(vinyl pyrrolidone) stabilizer

Ion-free latices of styrene-butadiene rubber (SBR) and nitrile-butadiene rubber (NBR) were synthesized by emulsion polymerization with use of poly (vinyl pyrrolidone) (PVP) stabilizer. The goal was to prepare ion-free latex films, possessing dual-phase latex particle morphology, and swell the films with liquid electrolyte to yield dual-phase polymer electrolytes (DPE). SBR/PVP latex was prepared readily, but NBR/PVP latex was sensitive to coagulation. Differential scanning calorimetric (DSC) and scanning electron microscopic (SEM) analyses of latex films provided morphological evidence concerning particle structure and phase separation. Blends of NBR/PVP and PB/PVP latices (PB = polybutadiene) were also investigated, but particle structure was not present in the blended latex film, even though particle structure was present in the individual NBR/PVP and PB/PVP latex films. After extensive swelling of SBR/PVP latex films, PVP was extracted from the films, and ionic conductivities greater than 10^?3 S/cm were achieved. © 1994-John Wiley & Sons, Inc.     

A correlation between the variable melt flow index and the molecular mass distribution of virgin and recycled polypropylene used in the manufacturing of battery cases

This study looked at establishing a correlation between the variable melt flow index (VMFI) values of molten polypropylene (PP) with different piston-load masses using a standard MFI analyser. The study was done using virgin PP and recycled PP obtained from recycling Pb-acid batteries. The study showed that the results would fit a suitable power function equation where the size of the exponent reflects the increase in flow characteristics of the polymer with increased piston-load mass. The established correlation was then compared to the average molecular weight distribution of virgin PP determined by gel permeation chromatography (GPC). Good agreement was obtained for the range of grades of virgin PP samples that correlated well with the Mark-Houwink power law where the inverse of the MFI (1/MFI) would be proportional to the average molecular weight to the power of 3.4 (Mw^3.4). GPC analysis cannot be effectively used to study recycled PP, where a number of factors can influence the melt flow properties such as fillers, impurities and the presence of polyethylene in the polymer matrix. Instead, a comparative understanding of the flow behaviour of recycled PP to that of virgin PP was done by using the VMFI method to possibly show the dissimilar polymer melt flow behaviour of using virgin and recycled PP material in injection moulding of new battery cases and lids, or when attempting to seal the lid to the battery case during manufacturing.     

Degradation behavior of maleated polyethylene/ground tire rubber thermoplastic elastomers with and without stabilizers

This work investigates the effects of different degradation processes (weathering, thermal ageing and re-extrusion) on maleated polyethylene (MAPE), as well as MAPE/ground tire rubber (GTR) thermoplastic elastomers with and without stabilizers (thermal stabilizer, UVA and HALS). Mechanical characterizations revealed that GTR addition reduced compounds stability against thermal ageing at both 80 and 90 °C. But addition of stabilizers increased thermal stability of the MAPE phase. However, the results suggest that the stabilizers had no effect on the GTR phase. Mechanical characterizations also showed that weathering caused degradation in MAPE, while presence of stabilizers decreased the effects of degradation. Addition of GTR also increased significantly the stability of MAPE against weathering (due to presence of carbon black in GTR). Re-extrusion resulted in lower MAPE modulus (due to decreased molecular weight), while the modulus of GTR filled compounds increased. Re-extrusion also led to decreased GTR average particle size, especially at higher GTR contents. Morphological analyses showed that thermal ageing and re-extrusion did not change significantly blend morphology, but weathering, on the other hand, led to severe degradation of both MAPE and GTR filled compounds surface. Compression set of MAPE/GTR compounds was found to decrease with increasing degradation level (due to crosslinking). Finally, sample density slightly increased with degradation level (also due to crosslinking).     

Thiol-ended polyethylene oxide as reactive stabilizer for dispersion polymerization of styrene

 Radical dispersion polymerization of styrene in aqueous ethanol solutions was performed in the presence of a new reactive polyethylene oxide stabilizer with thiol end groups. This reactive stabilizer was compared to the more conventional poly (N-vinyl pyrrolidone). Particles size distribution, molecular weights and kinetics were investigated. Monodispersed polymer particles with diameter in the range 200–2000 nm were obtained depending on the amount of stabilizer used. In all cases, the polyethylene oxide (PEO) sequence of the dispersant was partly incorporated at the surface of the latex particles, but the grafting yield of polyethylene oxide chains was always limited and did not exceed 15%. Part of the stabilizer being unreacted or reacted with low molecular weight polystyrene remained in the continuous phase. Received: 26 September 1996 Accepted: 4 March 1997     

Basalt fibre-reinforced high density polyethylene composite development using the twin screw extrusion process

Offshore renewable energy can lead the way towards sustainable energy harvesting and support the achievement of the CO2 reduction target by 2030. To achieve this goal it is necessary to decrease the manufacturing and deployment cost of the offshore devices. This paper focusses on the mechanical, chemical and microstructural assessment of a novel high density polyethylene (HDPE) reinforced with short basalt fibres for potential application as a hull material for wave energy devices. The choice of short fibres ensures the new composite can utilise existing low cost manufacturing methods for HDPE structures. In particular this study compares the properties of material with a recycled HDPE matrix with the properties of a material using a virgin HDPE matrix. The mechanical properties achieved by the novel composites exceed an improvement of ~300% in the properties of the monolithic polymer hence indicating the potential of this material, both for recycled and virgin HDPE. Furthermore, exploration in detail of the interaction fibres/matrix indicated the dynamic reaction between coupling agent and polymeric matrix showing the formation of molecular bonding perpendicular to the fibres, hence enhancing a 3D network that further increases the reinforcement abilities of the fibres.     

EB-promoted recycling of waste tire rubber with polyolefins

Despite the fact that more and more methods and solutions are used in the recycling of polymers, there are still some problems, especially in the recycling of cross-linked materials such as rubber. Usually the biggest problem is the lack of compatibility between the cross-linked rubber and the thermoplastic matrix. In this study we applied ground tire rubber (GTR) as recycled material. The GTR was embedded into polyethylene (PE) and polyethylene/ethylene-vinyl acetate copolymer (PE/EVA) matrices. In order to increase the compatibility of the components electron beam (EB) irradiation was applied. The results showed that the irradiation has a beneficial effect on the polymer–GTR interfacial connection. The EB treatment increased not only the tensile strength but also the elongation at break. The irradiation had also positive effect on the impact strength properties.     

基于乘用车轮胎胎面胶粉的再生橡胶的制备及性能

通过力化学再生法制备了以废轮胎胶粉为原料的再生橡胶，研究了不同活化剂420用量对再生橡胶性能的影响，测试表明：再生橡胶含硫键断裂生成了硫自由基，随着活化剂含量的增加，再生橡胶的邵氏硬度和交联密度持续降低；拉伸强度、断裂延伸率和凝胶含量均先升高后降低，在活化剂用量为0.9 phr时，拉伸强度和断裂延伸率最大，再生橡胶的凝胶含量最大为19.7%。 微观形貌发现，废轮胎胎面胶粉的颗粒较为分散，再生橡胶的结构颗粒相互粘连，孔洞和缺陷较多，再生橡胶的门尼黏度随着活化剂含量的增加而降低。 综合来看，活化剂420的最佳含量为0.9 phr，再生橡胶各项性能最优。     

Thermal characterization of UHMWPE stabilized with natural antioxidants

This work presents a study of the thermal degradation of ultra-high molecular mass polyethylene (UHMWPE) stabilized with natural (α-tocopherol and carvacrol) and synthetic antioxidants. Thermogravimetric analysis in dynamic mode was used to determine the apparent activation energies of different samples. The stabilization of UHMWPE with low concentrations (around 0.3%) of α-tocopherol is enough to obtain an efficient thermal performance of the polymer. Carvacrol is also a good stabilizer for UHMWPE, but at higher concentration than in the case of α-tocopherol. The comparison of apparent activation energy between samples with natural and synthetic antioxidants in similar concentration shows that α-tocopherol is a better stabilizer in terms of their thermal performance.     

改性沥青中橡胶含量的高效液相色谱测定法

用高效液相色谱法测定了改性沥青中橡胶的含量。柱温30℃,检测波长222 nm,流动相为同等比例的正己烷、四氢呋喃和乙腈的混合液,UV检测器。该方法的相对标准偏差RSD≤1.5%,线性方程:y=800.94x+579.03,线性相关系数r=0.999 8。     

Diffusion des additifs du polyethylene—I: Influence de la nature du diffusant

Chemical efficiency and stabilizer migration are the most important factors to be considered in connection with the ageing of polyethylene. This paper gives diffusion coefficients and solubilities for various industrial additives in low density polyethylene. The results, together with activation energies for diffusion, allow study of the diffusion process. It seems that it is necessary to consider deformations of the diffusing molecules and the polymer molecules. Additives of low molecular weight diffuse as gases, those of high molecular weight behave like polymer chains in self-diffusion.     

Silica Aerogel-Rubber Composite: A Sustainable Alternative for Buildings’ Thermal Insulation

Silica aerogel composites with recycled tire rubber have been synthesized and evaluated for their potential use for thermal protection in buildings. The present work describes for the first time the preparation of silica-based aerogel composites containing recycled rubber tires reinforced with polyvinyl butyral (PVB) by hot pressing. The developed composite was extensively characterized regarding its physical, morphological, thermal and mechanical features, and the results showed their properties were relevant, leading to composites with different properties/performances. The obtained bulk density values were satisfactory, down to 474 kg·m⁻³, and very good thermal properties were achieved, namely, thermal conductivity as low as 55 mW·m⁻¹·K⁻¹ for composites with silica aerogel, recycled tire rubber and PVB. The most promising composites were those based on low bulk density and thermal conductivity values, and they were thermally stable, indicating their suitability for thermal insulation applications.