Ultrathin Silicon-Compound Barrier Coatings for Polymeric Packaging Materials: An Industrial Perspective

Growing demands for increased shelf-life of food products and chemical inertia of the contact surfaces have stimulated development of polymers with improved high-barrier properties. Our objectives in this article are (1) to describe experimental results on Plasma-enhanced chemical vapor deposition (PECVD) and its importance to produce thin layers of inorganic glassy barrier materials for food, pharmaceutical, and organic display applications; (2) despite the thereby greatly enhanced quality of film or rigid packaging material, some residual coating defects result in less-than-perfect gas, moisture and aroma barriers: an innovative technique based on reactive ion etching (RIE) in oxygen plasma is also presented, along with a staining method, which render even sub-m coating defects visible. Data are shown for oxygen transmission rate on virgin and defective coatings, and the industrial context and applications are presented.     

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO₂ [P(St-BA-AA)/SiO₂] nanocomposites by in situ formation of SiO₂ nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Surface modification of confined microgeometries via vapor-deposited polymer coatings

The development of generally applicable protocols for the surface modification of complex substrates has emerged as one of the key challenges in biotechnology. The use of vapor-deposited polymer coatings may provide an appealing alternative to the currently employed arsenal of surface modification methods consisting mainly of wet-chemical approaches. Herein, we demonstrate the usefulness of chemical vapor deposition polymerization for surface modification in confined microgeometries with both nonfunctionalized and functionalized poly(p-xylylenes). For a diverse group of polymer coatings, homogeneous surface coverage of different microgeometries featuring aspect ratios as high as 37 has been demonstrated based on optical microscopy and imaging X-ray photoelectron spectroscopy. In addition, height profiles of deposited polymer footprints were obtained by atomic force microscopy and imaging ellipsometry indicating continuous transport and deposition throughout the entire microchannels. Finally, the ability of reactive coatings to support chemical binding of biological ligands, when deposited in previously assembled microchannels, is demonstrated, verifying the usefulness of the CVD coatings for applications in micro/nanofluidics, where surface modifications with stable and designable biointerfaces are essential. The fact that reactive coatings can be deposited within confined microenvironments exhibits an important step toward new device architectures with potential relevance to bioanalytical, medical, or "BioMEMS" applications.     

Synthesis of core-shell silver colloidal particles by surface immobilization of an azo-initiator

Silver nanoparticles, with the diameter of approximately 100 nm, were coated with a 5–10 nm layer of poly(styrene-co-4-styrenesulfonic acid sodium salt). Polymerization was initiated on the particles by a surface adsorbed 4,4-azobis(4-cyanovaleric acid) initiator. FTIR, electron microscopy, dynamic light scattering, and optical spectroscopy were employed to differentiate between the original and coated particles.     

Barrier properties of polymer/alumina nanocomposite membranes fabricated by atomic layer deposition

Novel polymer/ceramic nanocomposite membranes were fabricated, characterized and tested for their barrier performance. Atomic layer deposition (ALD) was used to deposit alumina films on primary, micron-sized (16 and 60 μm) high-density polyethylene (HDPE) particles at a rate of 0.5 nm/cycle at 77 °C. Well-dispersed polymer/ceramic nanocomposites were obtained by extruding alumina coated HDPE particles. The dispersion of alumina flakes can be controlled by varying the number of ALD coating cycles and substrate polymer particle size. The diffusion coefficient of fabricated nanocomposite membranes can be reduced to half with the inclusion of 7.29 vol.% alumina flakes. However, a corresponding increase in permeability was also observed due to the voids formed at or near the interface of the polymer and alumina flakes during the extrusion process, as evidenced by electron microscopy. The low surface wettability of the alumina outerlayers was believed to be one of the main reasons of void formation. Particle surface wettability was improved using 3-aminopropyltriethoxysilane (APS) to coat the particle ALD surface modified polymer particles prior to extrusion. The diffusion coefficient and permeability of the membrane using surfactant-modified particles decreased by 20%, relative to the non-modified case.     

Reproducing Superhydrophobic Leaves as Coatings by Micromolding Surface‐Initiated Polymerization

Micromolding surface‐initiated polymerization enables the fabrication of polymer coatings that reproduce the microscale surface topography of superhydrophobic leaves onto solid supports. Here, the surfaces of superhydrophobic leaves from Trifolium repens and Aristolochia esperanzae are molded and reproduced as the topography of a partially fluorinated polymer coating through the surface‐initiated ring‐opening metathesis polymerization of 5‐(perfluorooctyl)norbornene (NBF8). The polymer coatings have thicknesses exceeding 100 μm, which can be tailored by the amount of monomer added to the mold. These coatings are robustly bound to the substrate, contain compositions not found in nature, and achieve superhydrophobicity that is comparable to the actual leaf.

     

Alteration of Structure and Properties of Thin Polyimide Films and Coatings by Plasma and Thermal Treatment

The influence of alternating radiofrequency-plasma and heat treatment on the structure and bulk properties of polyimide films and coatings with a thickness of 3.5 m was studied. It was shown that plasma treatment leads to the enhancement of the specific surface energy due to the polar component and to an increase in the diffusion coefficient and in the amount of sorbed water. The subsequent thermal treatment leads to the recovery of the polyimide surface and bulk properties to almost their initial magnitudes. It was assumed that these effects are caused by a change in the structure of thin films and coatings and by the buildup of negatively charged particles at the surface and in mesopores of the polymer upon RF plasma treatment and due to annealing upon thermal treatment.     

IR laser ablative decomposition of poly(vinyl acetate) loaded with Fe and Cu particles

Pulsed IR laser-induced decomposition of poly(vinyl acetate) (PVAC) loaded with nanometer-sized Cu and micrometer-sized Fe particles results in the formation of gaseous products and deposition of polar crosslinked polymer films which contain metal (Cu and Fe) particles. The main volatile products are hydrocarbons, carbon oxides (CO and CO₂), molecular hydrogen and acetic acid. The deposited polymer films were characterized by FTIR, UV and XP spectra and by electron microscopy and thermogravimetry. They contain reactive conjugated CC bonds and ca. 50% of the initially present acetate groups. Residual reactivity of the CC bonds results in polymer crosslinking and decrease in solubility. The deposited, crosslinked PVAC-based films containing metal particles are less thermally stable than similar films not containing these particles. The reported process reveals feasible ablation of metal particles when embedded in a polymer and makes it possible to fabricate films of metal/polymer composites in which metal particles are completely protected by the polymer.     

Surface modification of a liquid‐crystalline polymer for copper metallization

The effects of different surface modifications on the adhesion of copper to a liquid‐crystalline polymer (LCP) were investigated with X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, contact‐angle measurements, and pull tests. High pull‐strength values were achieved when copper was sputter‐deposited onto plasma and reactive‐ion‐etching (RIE)‐pretreated LCP surfaces. The values were comparable to the reference pull strengths obtained with laminated copper on the LCP. The adhesion was relatively insensitive to the employed feed gas in the pretreatments. The surface characterizations revealed that for RIE and plasma treatments, the enhanced adhesion was attributable to the synergistic effects of the increased surface roughness and polar component of the surface free energy of the polymer. However, if the electroless copper deposition was performed on RIE‐ or plasma‐treated surfaces, very poor adhesion was measured. Good adhesion between the LCP substrate and electrolessly deposited copper was achieved only in the case of wet‐chemical surface roughening as a result of the creation of a sufficient number of mechanical interlocking sites, together with a significant loss of oxygen functionalities, on the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 623–636, 2003     

Variation of surface unevenness of anomalous composite polymer particles produced by the stepwise heterocoagulation of small particles onto large particle by heat treatment

Variation of surface unevenness of anomalous composite polymer particles produced by the stepwise heterocoagulation, which we had suggested in previous articles, of small cationic polymer particles onto large anionic polymer particle (LP) by heat treatment was examined with transmission and scanning electron microscopes. When the anomalous polymer emulsion was kept at higher temperature than the glass transition temperature ofLP, the particle surfaces were continuously changed from uneven to smooth state with the treatment time.Part CXLII of the series of Studies on Suspension and Emulsion     

Analysis of ″stepwise″ heterocoagulation process of small cationic polymer particles onto large anionic polymer particles using dynamic light scattering

In order to clarify in detail the process of the stepwise heterocoagulation of small polymer particles (SP) onto large polymer particles (LP), which we proposed to prepare anomalous polymer particles, the particle-size distribution in each step was estimated using dynamic light scattering.SP andLP have surface charges opposite to each other in emulsion states.SP were produced by emulsion copolymerization of styrene and methacryloyloxyethyltrimethylammonium chloride, andLP by emulsion terpolymerization of styrene, butyl acrylate, and methacrylic acid. Both emulsions in which nonionic emulsifier had been added were blended without coagulation and then the heterocoagulation was carried out by adjusting of the pH and heating.Part CXVII of the series Studies on Suspension and Emulsion.     

Are the Interactions between Recombinant Prion Proteins and Polymeric Surfaces Related to the Hydrophilic/Hydrophobic Balance?

New non‐fouling tubes are developed and their influence on the adhesion of neuroproteins is studied. Recombinant prion proteins are considered as a single component representative of hydrophobic proteins. Samples are stored for 24 h at 4 °C in tubes coated with two different coatings: poly(N‐isopropylacrylamide) as a hydrophilic surface and a plasma‐fluorinated coating as a hydrophobic one. The protein adhesion is monitored by ELISA tests, XPS and confocal microscopy. It appears that the highest recovery of recombinant prion protein in the liquid phase is obtained with the hydrophilic surface while the hydrophobic character of the storage tube induces an important amount of biological loss. However, the recovery is not complete even for tubes coated with poly(N‐isopropylacrylamide).

     

Adsorption behavior of polymers having phosphoric acid group on γ-Fe2O3 and magnetic characteristics in magnetic coatings

Polymers having phosphoric acid groups were prepared as a model binder for magnetic coatings, and the correlation among the adsorption behavior of the polymers onto-Fe₂O₃ particles and the dispersibility, the orientation, and the packing density of-Fe₂O₃ particles in the magnetic coatings was investigated.PMMA homopolymer molecules hardly adsorbed on-Fe₂O₃, and the interfacial tension at a water/polymer solution (toluene) interface ( _W/T) was scarcely changed compared with a water/toluene interface. Increasing with the content of polymeric phosphoric acid group, the adsorbance of polymer increased and the interfacial tension ( _W/T) decreased. When the content of polymeric phosphoric acid groups was over 0.4 mol%, the adsorbance of polymer and interfacial tension ( _W/T ) remained constant. When these polymers were used as a binder for magnetic tapes, the dispersibility of-Fe₂O₃ in the magnetic coatings was improved, increasing with the content of polymeric phosphoric acid group; however, when the content of phosphoric acid group was over 0.2 mol%, its dispersibility decreased abruptly.Studies on Recording Magnetic Materials and Magnetic Composite. XVIII.     

Epoxy Coatings with Low Surface Energy from Powdered Compounds Modified with Finely Dispersed Polytetrafluoroethylene Particles

Highly hydrophobic epoxy coatings with the surface energy as low as 14.5 mJ m^–2 and contact angles with water of 120°–150° were prepared from powdered compounds modified with less than 2 wt % finely dispersed polytetrafluoroethylene particles by dry mixing. As shown by scanning electron microscopy, EDX microanalysis, and atomic-force microscopy, the film formation at 180°С and formation of a polymer network matrix are accompanied by predominant migration of polytetrafluoroethylene particles to the air/coating interface, leading to gradient distribution of fluorine across the film and significant enrichment of the coating surface with fluorine. By varying the polytetrafluoroethylene content, it is possible to obtain hydrophobic coatings with satisfactory physicomechanical properties, smooth or rough surface, including micrometric and nanometric roughness, and different surface energy.     

Mechanochemical synthesis of polymer π complexes on the newly formed surface of lithium fluoride

The possibility of the mechanochemical synthesis of polymer complexes on a newly formed surface of finely divided particles under conditions of combined vibrodispersion of LiF-PVC and LiF-maleic anhydride systems was established. Some optical, electric, and magnetic properties of the resulting polymer organic complexes are discussed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2730–2736, December, 1990.     

Surface properties of biospecific coatings based on polyelectrolyte complexes of maleic acid copolymers

The surface properties of PE with bilayer and multilayer coatings based on polyelectrolyte complexes of the biospecific modified N-vinylpyrrolidone-maleic acid copolymer with chitosan, amphiphilic chitosan, or albumin have been investigated by atomic force microscopy, multiple attenuated total reflection spectroscopy, X-ray photoelectron spectroscopy, and goniometry. The copolymer of N-vinylpyrrolidone and maleic acid contains affine ligands to plasminogen—fragments of α-amino-bonded lysine—and imparts thromboresistant properties to the surface being modified. The surface morphology and the size of particles of deposited intermediate layers of chitosan or albumin differ from those of the bilayer (multilayer) coatings containing an additional external layer of the biospecific copolymer. The deposition of the multilayer polymeric coatings promotes a more thorough coverage of the protected surface. Characteristic absorption bands that demonstrate the presence of the modifying polymers on the PE surface have been revealed; this fact is also confirmed by the X-ray photoelectron spectroscopy data on the atomic composition of the analyzed surface. A significant increase in the hydrophilicity of the modified surface is established by the contact angle technique.     

Sol-gel zirconia coatings aimed at dust suppression in aluminosilicate high temperature insulating blankets

The feasibility of reducing the amount of loftable fibres in aluminosilicate blankets by coating with sol-gel zirconia was studied. A zirconium alkoxide based solution was employed to coat small samples of blanket using a dip-coating technique. The zirconia coatings and two grades of blanket were analysed using DTA, XRD, SEM and optical microscopy techniques to characterize any reactions and phase changes occurring in the system over a range of temperatures. It was found that dip-coated samples fired at temperatures of 700–800°C displayed reasonably coherent coatings providing an anchoring effect at the surface of the material by bonding loose surface fibres in a network of zirconia.     

Iron oxide film growth under ultrathin polysiloxane networks

This study focuses on the preparation and characterization of magnetic switchable thin iron oxide–polymer films. In a series of experiments, the formation and growth of iron oxide under ultrathin polysiloxane layers was controlled by changing the concentration of iron ions in the aqueous subphase or by varying the residence time of ammonia in the gas phase above the liquid sample. The growth of the combined film structures is studied in situ by interfacial rheology, optical microscopy, and x-ray scattering experiments and ex situ by scanning electron microscopy. Different stages of iron oxide aggregation, from a very thin layer of amorphous iron oxide with thickness of a few nanometers up to micrometer thick coatings of crystalline maghemite (γ-Fe₂O₃) were investigated. The specific interactions between the inorganic iron oxide and the polymer membranes cause the creation of new composite materials which are sensitive to magnetic forces.

Improving mechanical and biological properties of macroporous HA scaffolds through composite coatings

Interconnected porous hydroxyapatite (HA) scaffolds are widely used for bone repair and replacement, owing to their ability to support the adhesion, transfer, proliferation and differentiation of cells. In the present study, the polymer impregnation approach was adopted to produce porous HA scaffolds with three-dimensional (3D) porous structures. These scaffolds have an advantage of highly interconnected porosity (≈85%) but a drawback of poor mechanical strength. Therefore, the as-prepared HA scaffolds were lined with composite polymer coatings in order to improve the mechanical properties and retain its good bioactivity and biocompatibility at the same time. The composite coatings were based on poly(d,l-lactide) (PDLLA) polymer solutions, and contained single component or combination of HA, calcium sulfate (CS) and chondroitin sulfate (ChS) powders. The effects of composite coatings on scaffold porosity, microstructure, mechanical property, in vitro mineralizing behavior, and cell attachment of the resultant scaffolds were investigated. The results showed that the scaffolds with composite coatings resulted in significant improvement in both mechanical and biological properties while retaining the 3D interconnected porous structure. The in vitro mineralizing behaviors were mainly related to the compositions of CS and ChS powders in the composite coatings. Excellent cell attachments were observed on the pure HA scaffold as well as the three types of composite scaffolds. These composite scaffolds with improved mechanical properties and bioactivities are promising bone substitutes in tissue engineering fields.     

Photoelasticity and structure of PMMA networks

The optical anisotropy (=polarizability) of uniaxial deformed swollen and unswollen PMMA networks depends on the temperature. This is not in agreement with the Kuhn-Grün-theory. The temperature dependence and the negative values even above the glass transition temperatureT _g can be explained by the existence of associations which cause a hindrance of the ester side group mobility. The swelling of the network in the optical isotropic solvent carbon tetrachloride does not degrade the associations and therefore not change the network structure; onlyT _g decreases. The situation is more complicated if optical anisotropic solvents are used. Polar aliphatic and aromatic solvents degrade the associations to some extend and the birefringence is shifted to more positive values. An additional change is caused by specific polymer solvent interactions. Aromatic solvents form complexes with the ester side group and the aliphatic solvent chloroform completely degrades the associations, which can be explained by the formation of hydrogen bonds. Sign and magnitude of the optical anisotropy allow statements on the orientation of the solvent molecules with respect to the polymer chain or the ester side group.Vorgetragen von H. J. Kock auf der Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Fachausschuß Polymerphysik, Ulm 1983.