Conversion of plastic/cellulose waste into composites. I. Model of the interphase

This article proposes a mechanism for a significant improvement in the mechanical performance of a simulated waste fraction, composed of an immiscible low-density polyethylene (LDPE) and high-impact polystyrene (HIPS) blend (70:30 proportion), when chemithermomechanical pulp (CTMP) fibers and maleic acid anhydride grafted styrene–ethylene/butylene–styrene block copolymer (MAH-SEBS) were added. SEM micrographs of composites showed an increased contact between the continuous LDPE phase and CTMP fibers when the functionalized compatibilizer (MAH-SEBS) was used. By employing a model study using LDPE and regenerated cellulose, we investigated the interphase properties between the plastic phase and the cellulosic component. The model study utilized ESCA, FTIR, and contact angle analysis to follow the reaction between the cellulose surface and the functionalized compatibilizer. All three methods showed that MAH-SEBS was bonded to the surface of the cellulose. The single-fiber fragmentation test showed that the adhesion between cellulose fibers and the plastic matrix was significantly improved for MAH-SEBS–modified samples. The effect of enhanced adhesion on increased mechanical properties of cellulose composites is also discussed, and a prediction of composite strength given, based on interfacial adhesion promotion and fiber properties. © 1995 John Wiley & Sons, Inc.     

Improvement of adhesion between polyethylene and regenerated cellulose fibers by surface fibrillation

Regenerated cellulose fibers spun from straw pulp using the N-methylmorpholine N-oxide (NMMO) process were evaluated as a reinforcement for low-density polyethylene (LDPE). Surface fibrillation was carried out by a mechanical treatment to improve interfacial adhesion. Surface fibrillation resulted in a gradual change in surface topography, as detected by SEM. Long and numerous twisted fibrils were observed on the surface of the treated fibers. The fiber perimeters, determined by the Wilhelmy plate method, increased with an extended degree of fibrillation, while the strength of the fiber was not affected by the surface treatment. Model composites were prepared by embedding untreated and surface-fibrillated single fibers into an LDPE matrix, and the single fiber fragmentation (SEF) test was carried out to determine the critical fiber length. The interfacial shear strength (τ) was then calculated by applying a modified form of the Kelly-Tyson equation. It was found that the interfacial shear strength increased significantly as a result of surface fibrillation. The proposed mechanism for the improvement of interfacial adhesion is a mechanical anchoring between the matrix and the fiber.     

Determination of the degree of adhesion in plasma-treated polyethylene/paper laminates

It is shown that an oxygen or ammonia plasma treatment significantly improves the adhesion between low density polyethylene (LDPE) and cellulose. Plasma treatment of the polymer was more effective than treatment of the paper, and ammonia plasma seemed somewhat more effective than the oxygen treatment. The adhesion between polyethylene and cellulose was evaluated at room temperature using a non-linear double cantilever beam test. The effect of the discharge treatment on the surface composition of LDPE and cellulose was characterized using electron spectroscopy for chemical analysis. The improved adhesion may be due to an improved penetration of the porous paper surface by the LDPE-melt and to an increase in the interfacial attraction forces as a result of the introduction of polar groups in the surfaces.     

The preparation and characteristics of low-density polyethylene composites containing cellulose treated with cellulase

Low-density polyethylene (LDPE) composites containing untreated cellulose, cellulose treated with cellulase, and cellulose treated with cellulase after pretreating with NaOH were prepared. The purpose of the cellulase treatment of cellulose is to enhance the interfacial adhesion between the cellulose and the matrix. The effect of this treatment was studied by viscometry and X-ray diffraction. Maleic anhydrideg-polythylene (MAH-PE) was also added to the composite to enhance interfacial interactions between the cellulose and the matrix and to increase the dispersibility and the wettability of cellulose. The increased adhesion in composites containing the treated cellulose and MAH-PE was studied by FTIR. In addition, the thermal, dynamic mechanical, and tensile properties of the composites were investigated. When MAH-PE was added to the composite, it was found that the reaction between MAH-PE and treated cellulose occurred more easily.     

Rheological and mechanical properties of cellulose/LDPE composites using sustainable and fully renewable compatibilisers

Cellulose composites with polyethylene (PE) permit to reinforce this commodity polymer, while at the same time introducing renewable content and thus minimizing the use of petroleum-based feedstocks. Herein, we report on two fully renewably sourced and sustainably synthesized compatibilisers based on amylose and starch, which allow for such cellulose dispersion in low-density PE (LDPE). These compatibilisers advantageously combine the hydrophilicity of carbohydrates with the hydrophobicity of fatty acids. Upon extrusion of cellulose, LDPE, and the compatibilisers, a significantly improved dispersion of cellulose within LDPE was observed using rheology at loadings of 10 wt % cellulose and 5–15 wt % compatibiliser. Moreover, an improved interfacial adhesion was observed using scanning electron microscopy and was also confirmed by the mechanical properties, notably the Young's modulus, as a result of the good stress transfer between filler and matrix material. This study highlights the potential of fully renewable compatibilisers for the preparation of composites of cellulose and the commodity plastic LDPE. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48744.     

Improving the adhesion of poly(ethylene terephthalate) fibers to poly(hydroxyethyl methacrylate) hydrogels by ozone treatment: Surface characterization and pull-out tests

This work reports a methodology to improve the adhesion between poly(ethylene terephthalate) (PET) fibers and poly(hydroxyethyl methacrylate) (pHEMA) hydrogels by treating PET with ozone. The surface chemistry of PET was examined by water contact angle measurements, X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS) and attenuated total reflectance infrared spectroscopy (ATR-IR) yielding information about the chemical functionalities at depths upon 0.6 μm. Ozone treatment introduces several polar groups in the surface of PET through oxidation and chain scission resulting in increased wettability. These groups include mostly carboxylic and anhydride groups and in small extent hydroxyl groups. Atomic force microscopy (AFM) analysis shows that the surface of ozone-treated PET films is fully covered with spherical particles that are removed after washing the film with water. During the washing step carboxylic functionalities were removed preferentially, as demonstrated by XPS and IR analysis. According to pull-out tests, PET monofilaments and bundles treated by ozone had a higher adhesion to pHEMA hydrogels than untreated ones. The apparent interfacial shear strength is 65% higher on pHEMA hydrogel containing an ozonated than an untreated PET monofilament. In addition, the force to pull-out an ozone-treated PET bundle from pHEMA hydrogel is ca. 81% higher than the one observed for the untreated bundle.     

Plasma modification of cellulose fibers for composite materials

Composites of natural fibers and thermoplastics can be combined to form new enhanced materials. One of the problems involved in this type of composites is the formation of chemical bonds between the fibers and the polymers at the interface. This work presents a study where low energy glow discharge plasmas are used to functionalize cellulose fibers implanting polystyrene between the fibers and the matrix that improve the adhesion of both components. The interface of polystyrene was synthesized by continuous and periodic glow discharges on the surface of the cellulose fibers. The results show that the adhesion in the fiber–matrix interface increases with time in the first 4 min of treatment. However, at longer plasma exposures, the fiber may be degraded reducing the adhesion with the matrix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3821–3828, 2006     

Adhesion characteristics of oxygen plasma-treated rayon fibers

The effect of oxygen plasma treatment of fiber on the adhesion between regenerated cellulose fiber and polyethylene (PE) was investigated using the single-fiber fragmentation test. In addition to allowing the determination of the interfacial shear strength, the fragmentation test provided a great deal of useful information on shear stress transfer and failure mechanisms in the systems. It was found that oxygen plasma treatment considerably enhanced the interfacial adhesion, as established by both the shear strength values that were measured and the birefringence patterns observed. The influence of the duration of treatment on adhesion was studied and found to be a very important parameter. The roles of surface chemistry, surface energetics, and surface topography of fiber in the interaction balance were investigated using electron spectroscopy for chemical analysis (ESCA), contact angle measurements, and scanning electron microscopy (SEM). It was seen that neither the plasma-induced changes in the surface energetics nor those in the surface topography could have exerted a positive effect on adhesion. Instead, the improved adhesion was ascribed to covalent bonds formed between the fiber and the matrix, as hydroperoxides, which were created on the fiber surface by the plasma treatment, decomposed during the fabrication of single-fiber specimens.     

Surface photografting of low-density polyethylene films and its relevance to photolamination

Surface modifications of pristine and ozone-pretreated low-density polyethylene (LDPE) films were carried out via UV-induced graft copolymerization with a photoinitiator-containing, epoxy-based commercial monomer (DuPont Somos? 6100 for solid imaging and optical lithography) and also with the photoinitiator-free acrylic acid (AAc). The chemical composition and microstructure of the graft copolymerized surfaces were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). The concentration of surface grafted polymer increased with the UV illumination time and the monomer concentration. For LDPE films graft copolymerized with the epoxy-based monomer, surface chain rearrangement was not observed or was less well pronounced, due to the partial crosslinking of the grafted chains. Simultaneous photografting and photolamination between two LDPE films, or between a LDPE film and a poly(ethylene terephthalate) (PET) film, in the presence of either monomer system, were also investigated. The photolamination rates and strengths depend on the ozone pretreatment time, the UV illumination time, and the UV wavelength, as well as on the nature of the substrate materials. A shear adhesion strength approaching 150 N/cm² could be achieved with either monomer system, provided that the polymer films were pretreated with ozone. The failure mode of the photolaminated surfaces was cohesive in nature in the case of the photoinitiator-containing epoxy monomer, but was either cohesive or adhesional in nature (depending on the substrate assembly) in the case of the photoinitiator-free AAc monomer.     

Ozone treatment for improving the solubility of cellulose extracted from palm fiber

We investigated effects of ozone treatment on solubility of cellulose and chemical composition in cellulose extracted from palm fiber. The initial holocellulose, α-cellulose, and lignin contents of the extracted cellulose were 88.0, 81.9, and 8.75%, respectively. The extracted cellulose was treated with ozone and NaOH solution. Ozone treatment for 5 hr at 40°C using 3% citric acid decreased the lignin content from 8.75 to 2.71%. Under these conditions, the degree of polymerization (DP) of the cellulose decreased to 29 from 160 and the carboxyl content increased to 2.05 mmol/g. When the solid phase was treated with NaOH after ozone treatment, the mass of the solid phase decreased as the ozone treatment time increased. The lowest mass was 0.43 g. Additionally, the mass of cellulose regenerated from the liquid phase increased with increasing treatment time. The highest mass of regenerated cellulose was 0.54 g. The masses of the solid phase and regenerated cellulose obtained without ozone treatment under the same conditions were 0.76 and 0.18 g, respectively. These results suggest that ozone treatment improves the solubility of cellulose by converting hydroxyl groups in the cellulose to carboxyl groups and reducing the DP.     

Fabrication of the carbon paper by wet-laying of ozone-treated carbon fibers with hydrophilic functional groups

Carbon papers (CPs) have been widely investigated as a gas diffusion layer for high performance fuel cells. Herein we report the fabrication of the CP by wet-laying of ozone-treated carbon fibers (CFs) with hydrophilic functional groups. To improve the dispersion of CFs in water, the surface of the CFs was modified by the ozone treatment. The surface of the ozone-treated CFs contains hydrophilic functional groups such as C–O, CO and O–CO, which have been characterized by X-ray photoelectron spectroscopy. The negative charge of CFs determined by zeta potential was significantly increased after the ozone treatment, and the value was linearly decreased upon increasing ozone-treated time. Since ozone-treated CFs were better dispersed in aqueous solution than bare CFs, the CP prepared by a wet-laying process of ozone-treated CFs have higher porosity and gas permeability than that from bare CFs. In addition, the prepared CP from ozone-treated CFs showed better performance in I–V measurement of the single cell than those from bare CFs because of their high gas permeability.     

Effect of corona modification on the mechanical properties of polypropylene/cellulose composites

The effect of various corona treatment conditions on the mechanical properties of cellulose fibers/polypropylene composites was studied. The cellulose fibers and polypropylene were modified using a wide range of corona treatment levels and concentrations of oxygen. The treatment level of the fibers was evaluated using the electrical conductance of their aqueous suspensions. The mechanical properties of composites obtained from different combinations of treated or untreated cellulose fibers and polypropylene were characterized by tensile stress–strain measurements; they improved substantially when either the cellulose fibers alone or both components were treated, although composites made from untreated cellulose fibers and treated polypropylene showed a relatively small improvement. The results obtained indicate that dispersive forces are mostly responsible for the enhanced adhesion. The relationship between the electrical conductance of the fibers, the mechanical properties, and the mechanism of improved adhesion is discussed. © 1994 John Wiley & Sons, Inc.     

A conformational analysis approach to phenol-formaldehyde resins adhesion to wood cellulose

The energies of interaction between ortho-ortho, para-para and ortho-para-linked dihydroxydiphenylmethanes, obtained by the condensation of phenol and formaldehyde, with the surfaces of a schematic elementary crystal of cellulose I were obtained by conformational analysis techniques. The results indicated that adhesion of phenol-formaldehyde (PF) condensates to cellulosic surfaces can be enhanced by shifting the relative proportions of the type of methylene linkage during preparation of the resin. The three phenolic dimers were also shown to have better adhesion to the cellulose surface than water, indicating that the water resistance of PF-jointed lignocellulosic materials appears to be due to the water-resistance of the interfacial secondary bonds between resin and substrate, and not only to the water resistance of the cured resin itself.     

Pilot Studies of Ozonation for Inactivation of Artemia salina Nauplii in Ballast Water

A pilot-plant study was conducted in the Republic of Croatia to determine the applicability of ozonation for inactivation of non-indigenous species and to provide necessary information regarding use of ozone as a ballast water treatment option. Nauplii of the brine shrimp Artemia salina were used as model organisms to investigate the efficacy of ozonation at three different ozone dosages (2.4, 3.7 and 10.9 mg L^?1). Mortality of Artemia nauplii at 98.6%, was achieved after 3 h of exposure in ozone-treated water with the highest ozone dosage. Our results indicated that ozonation is a promising treatment for controlling non-indigenous and potentially invasive species; however, to draw more general conclusions, several species with higher level of resistance to ozone are required and will be studied in the future.     

Surface modification of low‐density polyethylene (LDPE) film and improvement of adhesion between evaporated copper metal film and LDPE

To improve the interfacial adhesion between evaporated copper film and low‐density polyethylene (LDPE) film, the surface of LDPE films was modified by treating with chromic acid [K₂Cr₂O₇/H₂O/H₂SO₄ (4.4/7.1/88.5)]/oxygen plasma. Chromic‐acid‐etched LDPE was exposed to oxygen plasma to achieve a higher content of polar groups on the LDPE surface. We investigated the effect of the treatment time of chromic acid in the range of 1–60 min at 70°C and oxygen plasma in the range of 30–90 sec on the extent of polar groups created on the LDPE. We also investigated the surface topography of and water contact angle on the LDPE film surface, mechanical properties of the LDPE film, and adhesion strength of the evaporated copper metal film to the LDPE film surface. IR and electron spectroscopy for chemical analysis revealed the introduction of polar groups on the modified LDPE film surface, which exhibited an improved contact angle and copper/LDPE adhesion. The number of polar groups and the surface roughness increased with increasing treatment time of chromic acid/plasma. Water contact angle significantly decreased with increasing treatment time of chromic acid/plasma. Combination treatment of oxygen plasma with chromic acid drastically decreased the contact angle. When the treatment times of chromic acid and oxygen plasma were greater than 10 min and 30 sec, respectively, the contact angle was below 20°. With an increasing treatment time of chromic acid, the tensile strength of the LDPE film decreased, and the film color changed after about 10 min and then became blackened after 30 min. With the scratch test, the adhesion between copper and LDPE was found to increase with an increasing treatment time of chromic acid/oxygen plasma. From these results, we found that the optimum treatment times with chromic acid and oxygen plasma were near 30 min and 30 sec, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1677–1690, 2001     

Selective surface modification of ethylene-vinyl acetate and ethylene polymer blend by UV–ozone treatment

Ethylene-vinyl acetate (EVA) copolymers intended for sport sole manufacturing may contain noticeable amounts of polyethylene (LDPE) for improving abrasion resistance and decrease cost; however, this blend (EVA–PE) had low polarity and showed poor adhesion. In this study an effective environmentally friendly and fast surface treatment based on UV–ozone has been used to increase the wettability, polarity and roughness of EVA–PE material. Both the length of the UV–ozone treatment and the distance between the material surface and the UV-radiation source were tested. The UV–ozone treated EVA–PE material was characterized by ATR-IR spectroscopy using Ge prism, water contact angle measurements, X-Ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Adhesion properties were obtained from T peel tests of as-received and UV–ozone treated EVA–PE/polyurethane adhesive/leather joints.The more extended length of treatment and the shorter UV source–substrate distance increased the wettability of the EVA–PE material. Oxidation of the EVA–PE surface was produced by UV–ozone treatment creating new carbonyl groups mainly, and the amounts of hydroxyl and carboxylic groups were increased. The UV–ozone treatment produced ablation and etching of the EVA–PE material surface, mainly in the vinyl acetate, creating a particular roughness consisting on ruffles with deep crevices; this topography was also produced by heating produced during UV–ozone treatment. For low length of UV treatment or high UV source–material distance, the modifications of the EVA–PE material were mainly produced in the ethylene causing the selective removal of vinyl acetate, whereas more aggressive conditions produced strong oxidation in the EVA–PE material. Finally, adhesive strength was noticeably increased in the UV–ozone treated EVA–PE/polyurethane adhesive joints, and a cohesive failure in the leather was obtained.     

Effects of ozone and chlorine dioxide on the chemical properties of cellulose fibers

The effects of ozone and chlorine dioxide on the structure of hardwood cellulose fibers were studied by chemical methods. Chlorine dioxide had very little effect on the cellulose degree of polymerization (DP_v), although 40–50% of the chlorine dioxide charged was consumed. By contrast, ozonation of the cellulosic fibers resulted in a substantial reduction in the cellulose DP_v. Increasing the ozone charge increased the extent of cellulose degradation. At an ozone charge of approximately 3 wt % (20 mol equiv/100 g of fiber), a 40% reduction in DP_v, as measured by cupriethylenediamine viscosity, was observed. A comparison of the cellulose DP_v values obtained for ozonated cellulose fibers reduced with sodium borohydride before the viscosity measurements increased confirmed that the primary reaction of ozone with the cellulose fibers was glycosidic bond cleavage, with only a small amount of cellulose oxidation taking place. A functional group analysis of the ozonated cellulose fibers revealed a slight increase in the amount of carbonyl groups introduced into the fibers. In addition, carbon dioxide was detected, which combined with the lack of change in the carboxyl group content, indicated that the oxidation mechanism likely occurred in a three‐step process: formation of the carbonyl groups, followed by oxidation to carboxyl groups, and finally, decarboxylation resulting in glycosidic bond cleavage. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1219–1223, 2004     

Studies on adhesion of polyethylene. Part I. Influence of functionality and phase transfer catalyst

Low-density polyethylene (LDPE) has been oxidized using phase transferred permanganate as an oxidant. The resulting surface modifications have been characterized by different methods and the consequent adhesion promotion has been characterized in terms of contact angle and peel strength measurements. From contact angle measurements using water and formamide liquid drops, reversible work of adhesion, and thence γ^p _s and γ-^d _s, the contributions of polar and dispersion components, respectively, have been calculated. The polar contributions increased in each oxidized LDPE relative to untreated LDPE and the surface energies also increased appreciably. The adhesion strengths between aluminium and untreated LDPE, as well as those between aluminium and oxidized LDPEs, have been examined by peel strength measurements. We found that the adhesion strength increased about 8-28 times in the case of oxidized LDPEs. Maximum strength was observed when benzyl triphenyl phosphonium permanganate was the oxidant. Both the peel force and the thermodynamic work of adhesion increase sharply with an increase in the carboxyl content, the total number of oxo groups, and the combined CO and COOH content. The dependence of these quantities on carbonyl content is either weak or even follows a reverse trend. It is proposed that the adhesion proceeds primarily through hydrogen bonds involving carboxyl group and/or coordinative bond formation between aluminium and epoxy and/or hydroperoxo groups.     

Surface modification of microfibrillated cellulose for epoxy composite applications

Microfibrillated cellulose (MFC) possessing a ‘web-like’ morphology was successfully modified with three different coupling agents: 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and a titanate coupling agent (Lica 38). The surface modification was confirmed using infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), and contact angle measurements. These modifications changed the surface character of MFC from hydrophilic to hydrophobic. The untreated and treated MFC were successfully incorporated into an epoxy resin system using acetone as the solvent. Better and stronger adhesion between the microfibrils and the epoxy polymer matrix was observed for the treated fibers, which resulted in better mechanical properties of the composite materials.     

The aging effects of repeated oxygen plasma treatment on the surface rearrangement and adhesion of LDPE to aluminum

The effects of aging temperature and time on the adhesion properties of oxygen plasmatreated low-density polyethylene (LDPE) were investigated. As the aging temperature and time increased, surface rearrangement and the migration of molecules containing polar functional groups into the bulk were accelerated to the surface to form a hydrophobic surface. The adhesion strength of oxygen plasma-treated LDPE/aluminum joints was measured using a 90° peel test by varying the plasma treatment time and aging temperature. The adhesion strength was constant, regardless of the plasma treatment time. As the aging temperature increased, the adhesion strength of the LDPE/aluminum joints decreased and the locus of failure changed from cohesive to interfacial failure. It was also found that the polar functional groups buried in the bulk could be reoriented to the surface in a polar environment. This study also investigated whether repeated oxygen plasma treatment would increase the concentration of polar functional groups at the surface and reduce the surface rearrangement and the migration of molecules containing polar functional groups during aging. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) showed that repeated oxygen plasma treatments increased the concentration of polar functional groups at the surface. However, the aging time between plasma treatments had a negligible effect on the concentration of polar functional groups at the surface.