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Composite fibres with a matrix of poly(ethylene glycol) (PEG) and cellulose nanofibrils (CNF) as reinforcing elements were produced using a capillary viscometer. Two types of CNF were employed: one based on carboxymethylated pulp fibres and the other on TEMPO-oxidized pulp. Part of the latter nanofibrils was also grafted with PEG in order to improve the compatibility between the CNF and the PEG matrix. The nominal CNF-content was kept at 10 or 30 weight-%. The composite fibres were characterized by optical and scanning electron microscopy in addition to dynamic mechanical thermal analysis (DMTA). Evaluation of the storage modulus indicated a clear reinforcing effect of the CNF, more pronounced in the case of the grafted CNF and depending on the amount of CNF. An interesting feature observed during the DMTA-measurements was that the fibrils within the composite fibres appeared to form a rather coherent and load-bearing network which was evident even after removing of the PEG-phase (by melting). An analysis of the modulus of the composite fibres using a rather simple model indicated that the CNF were more efficient as reinforcing elements at lower concentrations which may be associated with a more pronounced aggregation as the volume fraction of CNF increased.

Surface defects associated with manufacturing processes can severely impair the appearance of polymeric products. These defects can be enhanced with ageing (time, UV-light, heat and weather conditions). In the present contribution, the interest is focused on the defects generated during injection molding of elastomer-modified polymers that are often used in the automotive sector to produce interior and exterior components. In particular, defects denoted as “flow marks” or “tiger stripes” were investigated. Two different grades of elastomer-modified polypropylene (PP)-containing mineral fillers were studied here before and after heat ageing for 9 weeks at a constant temperature of 95°C. Although injection moldings are one of the grades that did not exhibit any flow marks, moldings of other PP-grade showed such defects and they were enhanced after the ageing process. The properties and structure of the glossy and the dull bands (as well as the effect of the thermal ageing) have been assessed by several characteristics such as microhardness, nanohardness, crystallinity, and surface composition. An increase in surface hardness was noted after the ageing treatment as a consequence of increased crystallinity. Dull and glossy bands also exhibited different values of the nanohardness, glossy bands were harder, and the dull bands appeared to be less crystalline. The surface composition of glossy and dull regions was slightly different; the surface regions of the glossy areas contained higher amounts of filler particles. The effect of the ageing on the striped appearance is furthermore discussed in relation to possible depletion of the stabilizer system. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Fibers produced by melt spinning of conductive polymer composites are attractive for several applications; the main drawback is however reduced processability at high filler concentrations. Carbon ...

Adding plate-like pigments such as talc or kaolin clay to a styrene-butadiene (SB) dispersion before coating paperboard on a pilot scale resulted in a coated material with improved water vapour barrier properties. Addition of paraffin wax further significantly reduced the water vapour permeability. A limited study was also performed using poly(vinyl alcohol) (PVA) as the matrix material and a similar result was obtained. In addition to the barrier properties, the surface characteristics (gloss, roughness, surface energy and chemical composition) and the printability of the coated substrate were evaluated. In general, it was found that the properties of the coated material were improved if the surface of the base substrate was smoothened prior to coating by a suitable surface treatment such as hot calendering or precoating. Such a treatment gave a more homogeneous coating film on the substrate. A comparison of the experimental results with the prediction of models for the effect of impermeable particles on the vapour permeability indicated that the pigments were not optimally dispersed (or oriented) in the coating layer. There is thus room for improvement. In a further series of experiments, nanoclays were incorporated into the coating layers. Exfoliation of the silicate layers was indicated in laboratory coating experiments using SB, but not on the pilot-scale coated materials. Thus no significant effects on the barrier properties were observed for such coated specimens. With PVA as the matrix polymer and low contents of the nanoclay, a marked decrease in the water vapour permeability took place, indicating a more pronounced exfoliation.

Paperboard was coated on a pilot scale using aqueous dispersions of styrene–butadiene (SB) copolymers in order to improve its surface characteristics (including printability) and barrier properties with regard to the transmission of water vapour. Coating the paperboard with the dispersion in two steps gave a smoother surface with a remarkable increase in gloss. The printing properties of the smoother double-coated surface were slightly better than those of the single-coated surface. Paraffin wax added to the latex dispersion reduced the water vapour transmission rate (WVTR) but had a negative effect on the printability of the board. The effect of two commonly used surface treatment techniques (corona and plasma at atmospheric pressure) on the printing and barrier properties of dispersion-coated (containing wax) paperboard was evaluated. A fairly intense corona treatment led to an undesirable increase in the WVTR-value. A less intense corona treatment preserved the WVTR-value to a great extent, but the printability remained at an unsatisfactory level. With plasma treatment, the water vapour barrier was not impaired, and the printability of the plasma-treated dispersion-coated (wax-containing) substrate was good. It is suggested that a better result using corona treatment may be obtained by optimising the power and controlling the time between the treatment and the printing, although this was not investigated here.

Polymer dispersions can be used for coating paper products in order to e.g. enhance their barrier properties. The influence of characteristics such as the degree of cross-linking (the gel content), glass transition temperature and degree of carboxylation of styrene–butadiene (SB) latex polymers on the mechanical properties and water vapour permeability of the corresponding polymer coating films at room temperature has been investigated. The storage modulus in the rubbery region increased markedly with increasing degree of cross-linking and the blocking (sticking tendency) towards adjacent paper substrates was in general somewhat lower at higher cross-link densities. There was also a tendency for the water vapour permeability to decrease somewhat with higher degrees of cross-linking. The degrees of carboxylation were quite low for the studied SB-dispersions and it had only a minor influence on the mechanical performance and barrier properties of the films. Reducing the glass transition temperature significantly below room temperature had a negative effect with regard to the blocking/sticking tendency of the polymer and on the water vapour permeability. On the other hand, a glass transition temperature significantly above room temperature resulted in a coating film with microcracks that caused a marked deterioration in the physical properties. These films were rather brittle with a low elongation at break. All the polymer films were also characterised using scanning electron microscopy, contact angle measurements and ESCA (electron spectroscopy for chemical analysis).

Aqueous dispersions of styrene–butadiene (SB) copolymers were used for coating paperboard in order to improve its surface characteristics and barrier performance with regard to water vapour. The SB-grades, which were chosen from a wider range of latices evaluated in an earlier study, differed in their degrees of cross-linking and carboxylation. An important result was that the performance (including a reduction in water vapour transmission rate) of the coated products was significantly enhanced by a pretreatment (precoating or high-temperature calendering) of the board. This was interpreted as being the result of a more homogeneous polymer layer on the substrate. In most cases, the paperboard was coated on a pilot scale and a higher drying temperature improved the film formation up to a certain limit. Too high a drying intensity resulted in the appearance of defects in the polymer layer. The differences in properties between the coated specimens that could be associated with the polymer characteristics were not marked, but a higher degree of cross-linking and a lower degree of carboxylation gave the best results. The water vapour transmission rate of the coated board was substantially reduced by the addition to the coating of a small amount of paraffin wax. Contact angle measurements and electron spectroscopy for chemical analysis (ESCA) indicated that this was due to a migration of the wax to the surface of the polymer film during drying. The wax addition also reduced the tendency for the polymer layer to stick (block) at elevated temperatures.

Desired savings in energy, raw materials and processing in the manufacture of coated papers may lead to the development of processes with reduced usage of water. One proposed process, the dry surface treatment (DST) for pigment-coating of paper has been studied in a laboratory scale. The treatment involves the application of dry, powdery coating materials on the paper surface and fixation of the deposited layer in a thermomechanical compression and smoothening phase in a heated roll nip. Electrostatic deposition of charged particles enables a non-contact coating application. In the previous studies, the DST-papers produced with two or multi-component powdery materials, that were formed by drying coating suspensions, exhibited coating coverage, surface strength and smoothness similar to commercial coated mechanical reference papers at equal coat weights, but a generally larger pore size of the dry-formed coatings gave higher levels of oil absorption, air permeability and somewhat irregular ink setting properties. This study aims to explore the possibilities to prepare the DST coating particles in a dry state. The eventual target is to obtain coating particles in the size range used in conventional pigment coating and adjust the binder properties, content and distribution in a favourable way with regard to the structure of the coating layer. Synthesis of particulate polymers under water-free conditions in supercritical carbon dioxide is described and performed. Hybrid coating particles, consisting of the pigment and binder together, were prepared and evaluated for their structure and the coating applicability.

It is well known that the properties of a final polymer product are determined not only by the polymer characteristics but also, via process-related structural changes, by the processing technique and by processing conditions such as cooling rate and machine speed. In this study, the influence of the extrusion coating process on the structure and properties of LDPE-, LLDPE-, and m-LLDPE-grades was evaluated. Process variables such as the melt temperature, the draw ratio, the length of the air gap between the die exit, and the laminating nip and the machine speed were studied. The primary interest was in the influence of the process parameters on the degree of orientation and its corresponding impact on the tensile and barrier properties (water vapor transmission rate) of the polymer films. The degree of orientation of the films, assessed by shrinkage measurements, was found to be directly related to the elongational strain rate imposed on the films during the drawing stage of the coating process. Furtherm...

The influence of the physical and chemical characteristics of a paper substrate coated with a thin homogeneous film of poly(vinyl alcohol) (PVA) has been investigated. Some of the paper specimens were temperature-gradient (TG) calendered (at high temperatures) before pilot-scale coating. Two different paper grades differing in structure and sizing formulation were used. For one of the grades, the high-temperature calendering had a slight effect on the chemical composition of the paper surface as evaluated by electron spectroscopy for chemical analysis. For the other grade, no such effect was noted. In the former case, it was suspected that the sizing in the paper substrate degraded and, as a consequence, that volatile hydrocarbons evaporated from the surface. The slight change in surface chemistry had no significant direct effect on the homogeneity of the applied polymer film. The results indicated that the surface roughness of the substrate was the governing factor. The low surface roughness obtained by TG-calendering was beneficial for the homogeneity and barrier properties. In one series of experiments, some of the paper substrates (uncalendered and calendered) were corona-treated before PVA-coating. This treatment greatly increased the wettability of the surface by water. In general, the corona treatment improved the homogeneity and the barrier properties (grease resistance, air permeability and water vapour transmission) of the applied film. The surface smoothness was clearly important also for the corona-treated papers.

Paper and board are often coated at high speeds with a mineral-based aqueous suspension in order to improve their printing properties. This suspension is usually called coating colour. The flow behaviour of the coating colour in the cavity of the short dwell coater (SDC) and in the vicinity of the blade tip when paper is coated with a stiff blade has been analysed using the finite element method. The models used to simulate the flow incorporated free surfaces and shear-thinning colours. The Newtonian case was in some cases also included in the modelling. The viscosity level and the shear-thinning character of the coating colour had a significant influence on the flow in the SDC cavity, although the overall behaviour was to a large extent governed by the speed of the coater. The pressure distribution along the paper surface in the SDC cavity was also analysed.

Aggregation in coating coluors is, in many cases, considered as a drawback since it may have negative consequences with regard to the runnability of the coluor. On the other hand, with a controlled ...

The mechanical properties of clay-based pigmented coating films bonded with a series of carboxylated styrene–butadiene latex binders have been investigated. The in-plane tensile strength and the elongation at rupture increased with increasing amount of polymeric binder. It is suggested that this is due to an improvement in stress transfer through the structure. The mechanical behavior of the films was furthermore found to be strongly related to the properties of the polymeric binder at the usage temperature. In torsional pendulum experiments an increase in the glass transition temperature of the polymeric binder was observed when it was incorporated in the coating film. This is interpreted as being the result of a decrease in the segmental mobility of the polymer molecules due to the presence of the clay particles, i.e., due to the interaction between the clay pigments and the binder. The interaction was, however, less noticeable in experiments using an NMR (nuclear magnetic resonance) technique. If the clay was replaced by calcium carbonate, a strong interaction, as measured using NMR, was observed between CaCO3 and the styrene–butadiene polymer, although the in-plane mechanical strength and ductility were reduced. A structural model accounting for some of the observed differences in mechanical behavior between clay-based and CaCO3-based coating films is suggested.

Coating colours used for the coating of paper and board consist mainly of a mineral pigment, which is very often clay, a synthetic binder such as a styrenebutadiene latex, dispersion agents and water retention aids. The latter are often water soluble polymers. These polymers have a very strong influence on the rheological properties of the coating colours, both on the strain rate dependence of the apparent viscosity and on the viscoelasticity. The effects of two different grades of carboxymethylcellulose (CMC) and one grade of hydroxyethylcellulose (HEC), on the rheological properties at room temperature of a clay-based coating colour at pH 8, have been investigated. It is concluded that the high values of the dynamic modulus of the colours are due to interactions between the cellulose derivatives and the solid particles, i.e. mainly the clay particles. For HEC this interaction is associated with adsorption of the polymeric molecules on the clay particles. In the case of CMC, the adsorption is strongly retarded by the presence of the dispersant (a polyacrylate salt). It is suggested that the marked elasticity of the CMC-containing colour in addition to a possible polymer adsorption may be due to charge interactions and/or depletion flocculation. The effect of CMC and HEC on the water-retention properties of the colour is also discussed.