Virgin Resin Research Articles

Modification of Rheological Properties of LDPE for Coating Applications

The effect of shear modification and blending on the coating performance of a commercial LDPE resin was studied. Shear modification of the virgin resin as well as of its blends with another LDPE was performed in single- and twin-screw extruders. The rheological properties of the modified materials were measured, and no significant differences in their behavior under shear deformation were detected. On the other hand, changes in the entrance pressure drop and extensional viscosity were observed. These changes in extensional behavior were found to affect coating properties. Overall, neck-in improved through shear modification, whereas it was not sensitive to blending with a higher-molecular-weight resin. On the other hand, blending had an effect on the draw-down speed, and it can be used to achieve a balanced coating performance.

Study of thermal and mechanical properties of virgin and recycled poly(ethylene terephthalate) before and after injection molding

In this study, we compared the thermal properties (glass transition, melting point and crystallinity) and mechanical properties (Young’s modulus, elongation at break and impact strength) of post-consumer poly(ethylene terephthalate) (PET) bottles with those of the virgin resin. We studied two types of scraps of recycled PET: one arising from homogeneous deposits of bottles and the other of heterogeneous deposits soiled by contaminants such as PVC and adhesives. The presence of contaminants and residual moisture coming in the shape of scraps facilitate the crystallization of recycled PET compared to virgin PET and induces cleavages of chains during the melt processing. This leads to a reduction in intrinsic viscosity and consequently in molecular weight, and these decreases are more significant when the recycled resin is soiled. Virgin PET exhibited a ductile behavior (>200% of elongation at break),whereas post-consumer PET bottles exhibited a brittle one (<10% of elongation at break). This is a consequence of the difference in crystallinity, the presence of impurities in the recycled PET and the different thermal and mechanical history of the virgin and recycled materials.

Study of the natural ageing of PVC insulation for electrical cables

The characterisation of high voltage cable insulation waste is addressed in an effort to determine their further utilisation either as feed in reprocessing or for the recovery of the energy and material content by pyrolysis. Electrically aged (18 years outdoors at 6–10 kV) polyvinyl chloride (PVC) cables were ground by mechanical or cryogenic procedures. The waste was studied in comparison with a PVC virgin resin and a PVC virgin formulation similar to that of the cables both in quantities of additives and structure of polymer. After successive extractions in acetone and benzene the base polymer and extracts were analysed by elemental analysis, GPC, viscometry, IR and 1H-NMR spectroscopy, TG, DSC, and several standard methods of plastic analysis (plasticizer absorption, static thermal stability, etc.). From the acetone extracted quantities and the plasticizer absorption measurements it appears that only 1–2% di-2-ethylhexylphthalate (DOP) was lost during the service-life of cables and most of the initial quantity remained in the cable composition so only a small addition is necessary for the reprocessing. The IR spectra of polymer extracted from electrical cable waste exhibit important changes concerning double bonds and carbonyl groups. The T g value is higher for the waste material indicating that it was rigidized due to the polyene fragments arising from partial dehydrochlorination. This is also supported by the viscometric and GPC measurements, the PVC from waste having a higher molecular weight than virgin PVC. Based on T g curves and static thermal stability the following order of thermal stability has been established: PVC waste jacket<PVC electrical cable waste<virgin PVC<PVC virgin cable formulation. One can conclude that PVC cable wastes have retained most of the characteristics required for reprocessing, but a higher level of stabilisers must be used to ensure the stabilisation of the deteriorated structure and compensate partial deactivation of the initial stabiliser system.

Solid-State Shear Pulverization of Plastics: A Green Recycling Process

A novel process called solid-state shear pulverization (S3P) has been developed at Northwestern University to recycle single or commingled postconsumer or preconsumer polymeric waste without sorting by type or color. This continuous, one-step process converts shredded plastic or rubber waste into controlled-particle-size powder ranging from coarse (10 and 20 mesh) to fine (80 mesh) or ultrafine (200 mesh). As a result, the pulverization product is usable in applications ranging from direct injection molding without prior pelletization, to rotational molding, to use in protective and decorative powder coatings, as well as to blending with virgin resins and compounding with additives. Scanning electron microscopy reveals that the fine particles have a unique elongated shape that is attributed to the high shear conditions occurring during the pulverization process. Injection-molded parts made from the powder product of the S3P process have mechanical and physical properties comparable to or better than the properties resulting from direct conventional processing of recycled single or commingled plastics. In addition, the parts made from the powder product of the S3P process are uniform in color, whereas parts injection-molded from multicolored recycled feedstock without prior pulverization via the S3P process are streaked, re during their commercial applicability. The improved mixing achieved via the S3P process is often accompanied by scission of the carbon-chain backbone of the polymers involved, as revealed by the generation of free radicals during S3P processing, associated mechanochemistry, and modification of the melt flow rate of the polymers by the S3P process. The implications of this chain scission process for in situ compatibilization of commingled plastic waste via S3P processing are discussed.

Mechanical and thermal properties of environment‐friendly “green” composites made from pineapple leaf fibers and poly(hydroxybutyrate‐co‐valerate) resin

AbstractThis paper presents the mechanical and thermal properties of unidirectional, degradable, environment‐friendly “green” composites made from pineapple fibers and poly(hydroxybutyrate‐co‐valerate) (PHBV) resin. Tensile and flexural properties of the “green” composites with different fiber contents were measured in both longitudinal and transverse directions. Compared to those of virgin resin, the tensile and flexural strengths of “green” composites are significantly higher in the longitudinal direction while they are lower in the transverse direction. However, the mechanical properties are lower than those predicted by simple models. Scanning electron microscope (SEM) photomicrographs of the tensile fracture surfaces demonstrate fibers being pulled out from the matrix, the interfacial failure, fiber fibrillation, and the nonunidirectional nature of the “green” composites. The thermal behavior of the “green” composites, studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), showed that the presence of pineapple fibers does not affect the nonisothermal crystallization kinetics, crystallinity, and thermal decomposition of PHBV resin.

The USA plastics recycling industry: a survey of manufacturers and vendors of recycled plastic products

Despite efforts spanning more than a decade, plastics continue to be the least recycled component of the USA's municipal waste stream. This study addresses a significant gap in knowledge about the operation of the plastics recycling market by investigating and analysing the characteristics and experiences of manufacturers and vendors of consumer products with recycled plastics content.The study collected information through a survey of this segment of the USA's plastics recycling industry. The analysis of this information confirmed that the industry, as a whole, is young. Nevertheless, it offers a very wide variety of products. These face stiff competition from virgin resin plastic products, or from other virgin competing materials such as wood and cotton. Recycled plastic products are often more expensive than their competitors. Some manufacturers and vendors, especially the younger ones, addressed this problem by finding a niche market with consumers who are willing to pay a premium for environmentally friendly products. On the other hand, companies whose products are successfully competing against virgin products are more likely to have operated longer, to be vertically integrated (producing raw materials and consumer products), and to be more diversified in the number of resins they handle.Manufacturers and vendors of recycled plastic products in the USA have gained considerable experience since the early years of plastics recycling. Nonetheless, they continue to face some serious challenges. Operators of materials recovery facilities that process PCR have an important role to play in supporting the industry by improving the quality of their product (i.e. PCR). However, the most important factor for securing continued growth of the industry is the expansion of markets for the industry's products. The responses to the survey indicate that, while there are actions that manufacturers and vendors can take to increase their chances of success, the effect of government policy remains overwhelming. Policymakers can facilitate growth in plastics recycling by stepping up their efforts to implement effective demand-side policies and by adopting policies to internalize the environmental and social externalities of plastics manufacturing and use.

Recyclability of PET from virgin resin

Bottle grade virgin PET (polyethylene terephthalate) resin was investigated through five consecutive injection molding steps to simulate recycling cycles. Tests were carried out after each recycling to evaluate degradation, crystallinity (by density and Differential Scanning Calorimetry-DSC measurements), hardness, and tensile and flexural properties. Consecutive recycling resulted in cumulative chain breaks caused by the material's contact with degrading agents such as temperature, oxygen, mechanical stresses, light, and water. In the fifth recycling step, for example, the number of carboxylic end groups, an indicator of the extent of chain-break, tripled in comparison to the initial molecule. The smaller chains that were formed fit more easily among the larger ones, thus increasing the percentage of crystalline phase in the structure. These two changes in the polymer's structure explained the recycled products' final properties, i.e., the injected samples became progressively harder and more fragile in each recycling step.

Production of Porous Carbon from Ion Exchange Resin Waste

The possibility to produce porous carbons with controlled micropores from waste ion exchange resins wasexamined. Two waste ion exchange resins were used as starting materials: one was used for desalination of water (Waste-P) and the other was used for refining suger (Waste-Gel). They were carbonized at 500 to 900°C were nonporousdue to thermal shrinkage. Waste-Gel contained about 7wt% of calcium, and Waste-P adsorbed organics. Then, to clarifythe effect of the impurities contained in the waste resins on the pore development, the virgin resins exchanged by calcium ion and those adsorbing phenol or fructose were prepared and carbonized. Calcium ion was found to greatly affect thecarbonization behavior of the resin, and consequently prevented the resin from shrinking thermally. On the other hand, the organics adsorbed enhanced thermoplastic property of the resin. When carbonized at 900°C, the Ca exchanged resinhad almost same pore volume distribution as the carbonized Waste-Gel had. This clarified that the pore developmentof the carbonized Waste-Gel is controlled by the calcium in the resin. The porous carbons produced from the waste resins had molecular sieving property to separate carbon dioxide from methane.

Interfacial and mechanical properties of environment-friendly green composites made from pineapple fibers and poly(hydroxybutyrate-co-valerate) resin

Physical and tensile properties of pineapple fibers were characterized. Tensile properties of pineapple fibers, like most natural fibers, showed a large variation. The average interfacial shear strength between the pineapple fiber and poly(hydroxybutyrate-co-valerate) (PHBV) was 8.23 MPa as measured by the microbond technique. Scanning electron microscopy (SEM) photomicrographs of the microbond specimens revealed an adhesive failure of the interface. Fully degradable and environment-friendly “green” composites were prepared by combining pineapple fibers and PHBV with 20 and 30% weight content of fibers placed in a 0°/90°/0° fiber arrangement. Tensile and flexural properties of these “green” composites were compared with different types of wood specimens. Even though tensile and flexural strength and moduli of these “green” composites were lower than those of some wood specimens tested in grain direction, they were significantly higher than those of wood specimens tested in perpendicular to grain direction. Compared to PHBV virgin resin, both tensile and flexural strength and moduli of these “green” composites were significantly higher. SEM photomicrographs of the fracture surface of the “green” composites, in tensile mode, showed partial fiber pull-out indicating weak bonding between the fiber and the matrix.

Toughening of epoxy resin using synthesized polyurethane prepolymer based on hydroxyl-terminated polyesters

Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by a relatively low toughness. One approach to improve epoxy resin toughness includes the addition of either a rigid phase or a rubbery phase. A more recent approach to toughen brittle polymers is through interpenetrating network (IPN) grafting. It has been found that the mechanical properties of polymer materials with an IPN structure are fairly superior to those of ordinary polymers. Therefore, the present work deals with epoxy resin toughening using a polyurethane (PU) prepolymer as modifier via IPN grafting. For this purpose, a PU prepolymer based on hydroxyl-terminated polyester has been synthesized and used as a modifier at different concentrations. First, the PU-based hydroxyl-terminated polyester has been characterized. Next, an IPN (Epoxy–PU) has been prepared and characterized using Fourier transform infrared (FTIR) spectroscopy, thin-layer chromatography (TLC), and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. In this study, a Desmophen 1200-based PU prepolymer was used as a modifier at different concentrations within the epoxy resin. The results also showed that, further to the IPN formation, the epoxy and the PU prepolymer reacted chemically (via grafting). Compared to virgin resin, the effect on the mechanical properties was minor. The impact strength varies from 3–9 J/m and Kc from 0.9–1.2 MPa m1/2. Furthermore, the incorporation of a chain extender with the PU prepolymer as a modifier into the mixture caused a drastic improvement in toughness. The impact strength increases continuously and reaches a maximum value (seven-fold that of virgin resin) at a modifier critical concentration (40 phr). Kc reaches 2.5 MPa m1/2 compared to 0.9 MPa m1/2 of the virgin resin. Finally, the SEM analysis results suggested that internal cavitation of the modifier particles followed by localized plastics shear yielding is probably the prevailing toughening mechanism for the epoxy resin considered in the present study. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2603–2618, 1998

Product design with glass fiber reinforced polymer blends, with potential applications in recycling

AbstractThis paper addresses the issue of compositional variation in multiphase, multi‐component polymer mixtures equivalent to those found in commingled waste streams, such as those obtained from reclamation/recycling operations of post‐consumer containers. By using virgin resins, the effects of variations in the composition of matrices containing high density polyethylene (HDPE) as the major phase on the properties of composites containing varying amounts of glass fiber and different adhesion promoters are studied. The results obtained on injection molded thin‐section parts indicate that it is possible, through the addition of glass fibers and in the presence of suitable adhesion promoters, to obtain enhanced and reproducible properties with relatively little dependence on matrix composition. Preliminary structural and flow analyses were performed with commercial software on different types of plastic parts that could be eventually molded from actual mixed waste plastics suitably modified through glass reinforcement. Experimentally generated rheological and mechanical property data on HDPE based blends containing 20 wt% glass fibers and different adhesion promoters were used for the simulation. Issues concerned with injection molding and product performance of glass‐fiber reinforced blends are discussed.

Grafting of polyethylenes by reactive extrusion. I. Influence on the molecular structure

Grafting of polyethylenes is an important method used in the modification of polyolefins with functional groups. Lately, the use of extruders as polymerization reactors has increased considerably. However, knowledge of the details of the reaction in the extruder is still limited. In this investigation, the grafting of various commercial polyethylenes, high-density polyethylenes (HDPEs), and linear low-density polyethylenes (LLDPEs) with diethyl maleate (DEM) was carried out in two corotating twin-screw extruders with different screw configurations and extrusion conditions. Two initiators at different concentrations were used. It was found that when the initiator level was raised in the LLDPEs the grafting degree increased and the molecular weight distribution of the grafted LLDPE2 did not show appreciable differences when they were compared to the virgin resin. On the other hand, the terminal vinyl group concentrations decreased at the expense of increasing the trans unsaturation concentrations. This last result is consistent with the formation of long-chain branching. Additionally, the weight-average molecular weight of grafted high-density polyethylene (HDPE1-g-DEM) decreased. The grafting efficiencies were consistent with the attained residence times and also with the kinetics of the decomposition of the peroxides. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 161–176, 1998

Recycling of polyethylene films used in greenhouses—Development of multilayer plastic films

Recycling of greenhouse plastic films was carried out by coextruding two-layer plastic films. The top layer consists of a blend of virgin thermoplastic resins stabilized with different stabilizers. The bottom layer was composed mainly of PE waste in combination with virgin resins and other ingredients. The two-layer films produced were subjected to accelerated UV ageing and to outdoor weathering in two different locations for almost 1 year. The results obtained revealed that the optimized two-layer films can be successfully used as greenhouse films.

Unsaturated polyester resins from glycolysed waste polyethyleneterephthalate : synthesis and comparison of properties and performance with virgin resin

Recycling of polyethyleneterephthalate (PET) bottles for soft drinks is accomplished by depolymerization through glycolysis. Obtained intermediates are reacted with mixtures of saturated and unsaturated acids to obtain unsaturated polyesters (UP) suitable for use as a matrix for fibre-reinforced thermosetting composites. The influence of chemical structure of glycols on the chemo-rheological behaviour of resins, has been verified. By using di-ethylene glycol, the behaviour of the resulting UP closely resembles that of UP obtained from virgin monomers. Moreover, composite sheets containing UP developed in the present research, show enhanced toughness if compared with the analogous composite made of virgin UP resin.

A review of plastics recycling in the USA with policy recommendations

SummaryPlastics are the fastest-growing component of municipal solid waste in the USA, and over the past decade there has been increasing public demand for plastics recycling. However, the necessity to separate the various plastic resins to make their recycling possible, combined with the low cost of virgin resins, make this technically difficult and expensive.Most sorting of plastic waste is done manually, and this method has been constrained to the diversion of only one or two types of plastics, because human sorters are incapable of distinguishing different plastics. A number of technologies are being developed in order to address this problem. Use of these technologies requires considerable capital investment and this makes many of them economically unfeasible at present. The federal, state, and local governments in the USA have continued to explore demand-side policy measures in an effort to promote market formation and operation. Where they have been successful, in the establishment of markets for recycled polyethylene terepthalate (PET), and high-density polyethylene (HDPE) resins, demand has outpaced supply, highlighting the need to find more effective methods to sort and divert different plastic resins. Even with these supply shortages, and with prices for virgin PET and HDPE at historic highs, however, most plastics recycling remains only marginally profitable. This demonstrates the need for continued policy support for the still-developing plastics recycling industry and recycled-plastics market.An analysis of the factors driving the recycling of PET, HDPE and polypropylene indicates that, as long as manual sorting is used, it would make sense for supply- and demand-side policies to focus on the recycling of particular plastic products that are easy to recognize, rather than resins that are not. Appropriate policies can help make specific products easily recognizable sources of specific resins. Such policies, implemented in conjunction with measures designed to facilitate capital investments and promote the establishment and operation of markets for all resins, are necessary to increase significantly the recycling of plastic waste above present levels.

Evaluation of Pet And Recycled Pet as Replacements for a Petg Packaging Tray

The purpose of this study was to determine if a thermoformed packaging part could be made more environmentally friendly. The goal was to replace the material originally qualified for a packaging tray-virgin polyethylene terephthalate glycol (PETG) copolyester-with a material which was then being recycled. The prime replacement material was polyethylene terephthalate (PET), possibly as virgin resin but preferably with a high recycled content, since that would have a more favorable environmental impact. Both virgin and 100% recycled PET were evaluated and compared with the PETG sheet. Important enduse properties for this transparent packaging tray were evaluatedincluding haze, gloss, impact strength, tensile strength and effects of orientation. Package drop testing was conducted to confirm the data from the mechanical property tests. Thermoforming trials demonstrated that both PET and recycled PET could be formed with state of-the-art equipment to provide adequate impact strength and other requirements of the final part.

Evaluation and Mapping of Heat-Shield Flight Temperature and Composition with Raman Spectroscopic Techniques

A Raman spectroscopic technique has been developed which can measure the maximum temperatures experienced by charring heat-shield materials and determine their post-test compositions (char, pyrolysis zone, and virgin resin). The technique has the capabilities of analyzing circular areas less than 0.1 mm in diameter or rectangles 0.1 mm in width and 2 mm in length. It can provide fine detailed surface and internal mappings and perform the analyses rapidly and conveniently in the laboratory following testing or flight recovery. Representative plots of temperature and composition profiles are provided. The data are compared with computations from the Charring Material Ablation (CMA) code.

Synthesis and Applications of Photodegradable Poly(Ethylene Terephthalate)

Abstract A novel synthetic route for the preparation of photodegradable poly(ethylene terephthalate) is described, along with procedures for the synthesis of 14C-labeled plastic. Studies of the labeled plastic in burial tests in active soil show that significant levels of biodegradation are achieved over a 2 to 3 year period for both photodegraded and virgin resin. Computer modeling studies are used to assess the desirability and energy cost of various disposal strategies.

Flexural Properties of Reinforced Polyester Concrete Made with Recycled PET

The flexural strength of steel-reinforced polymer concrete (PC) beams us ing unsaturated polyester resins based on recycled poly(ethylene terephthalate), PET, is reported in this paper. Investigation included mode of failure, moment-curvature response, variation of neutral axis depth with moments and the effect of tensile and compression steel reinforcement on the strength and ductility of the beams. This evaluation is not only important from the standpoint that resins based on recycled PET were used, but also because very few investigations have been done in this area with steel-reinforced PC using virgin resins.

Peroxide modification of linear low‐density polyethylene: A comparison of dialkyl peroxides

AbstractA commercial‐grade LLDPE resin was cross‐linked using three different dialkyl peroxides, at three different concentrations. The peroxides were ranked in order of their Cross‐linking efficiency and their effectiveness at increasing the storage modulus of the virgin resin at the cure temperature. The chemical mechanism by which the cross‐linking occurs is shown to be closely related to the changes in concentrations of reactive vinyl species on the polyethylene molecules, which follows well with proposed mechanisms of previous publications. Finally, a direct relationship is shown to exist between the rate of peroxide decomposition and the rate of increase in storage modulus of the rubbery modified resin during the curing reaction. © 1993 John Wiley &amp; Sons, Inc.