Improving the mechanical resistance of waterborne wood coatings by adding cellulose nanofibres

In the present study, microfibrillated cellulose (MFC) and nanocrystalline cellulose (NCC) were applied as additives for a waterborne acrylate/polyurethane-based wood coating in order to improve the mechanical resistance of coated wood surfaces. Coating mixtures containing up to 5 wt% nanocellulose were prepared by high-shear mixing and applied to wood substrates. The optical, mechanical and chemical properties of cured coatings were characterized. Surface roughness, gloss, scratch resistance, abrasion resistance and resistance against chemicals were determined according to the relevant European standards. Additionally, nanoindentation (NI) was used to assess the micromechanical properties of modified and unmodified coatings. Owing to a higher surface roughness, cellulose-filled coatings showed significantly lower levels of gloss than the unmodified coating indicating that nanocellulose acts as a matting agent. NI experiments revealed a slightly positive effect of nanocellulose addition on the hardness and modulus of the coatings. While scratch resistance improved consistently with increasing nanocellulose addition, abrasion resistance was found to improve only sporadically. Tensile tests on free-standing coating films revealed a significantly higher tensile strength and modulus for cellulose-filled coatings. Overall, the results suggest that the addition of cellulose nanofibres primarily improves the internal cohesion of the coating layer whereby MFC was more effective than NCC.     

The Effect of Radiation Dosages and UV/EB Radiation on the Properties of Nanocomposite Coatings

The aim of this study was to compare the effects of ultraviolet (UV) and electron beam (EB) radiation on the properties of cured nanocomposite coatings. Surface hardness increased with increasing radiation dosages (number of passes) for all samples. This was due to the increase in crosslinking with increasing radiation dosages. Pendulum hardness, gel content, and thumb twist results were analyzed to choose the appropriate curing dosage for both curing techniques. The selected dosages were then used to cure coatings for scratch and abrasion resistance tests. It was found that the UV curing produced coatings with better abrasion resistance, whereas EB curing was more suitable for producing scratch-resistant coatings.     

Effect of addition of surface modified nanosilica into silica–zirconia hybrid sol–gel matrix

An organic–inorganic hybrid sol (MZ) comprising a methacrylate functionalized silane matrix (M) and zirconium-n-propoxide (Z) was prepared using sol–gel technique. Two methodologies were adopted to modify the hybrid sol for generating nanocomposite coatings viz., (a) addition of acrylic surface modified silica nanoparticles (N) of diameter ～20 nm to the sol to enhance their compatibility with the hybrid sol–gel matrix and (b) in-situ formation of a three dimensional silica network by addition of tetraethoxy silane (T) to the sol MZ. In the first methodology, the sols were prepared with six different weight ratios of the nanoparticles to the sol, i.e. 0, 0.01, 0.05, 0.1, 0.25 and 1 which were labelled as MZ+Nx where x=0, 1, 2, 3, 4 and 5 respectively. The prepared sols were dip coated on 100 mm×100 mm polycarbonate substrates followed by thermal curing at 130 °C. The coatings were characterized for their mechanical properties like pencil scratch hardness, scratch resistance using scratch tester, nanoindentation hardness, and abrasion resistance as well as visible light transmittance. FT-IR studies were also carried out on heat-treated gels derived from the sols. A maximum pencil scratch hardness of 3H was obtained for the MZ+T coatings and these coatings withstood a critical load of 4.3±0.7 N before failure during scratch test. The maximum nanoindentation hardness of 3.8±0.01 GPa was obtained for the MZ+N5 coatings. The abrasion resistance of MZ+T coatings was higher when compared to MZ+N0 and MZ+N5 coatings. The scratch and nanoindentation hardness were seen to be better for an in-situ formed –Si–O–Si– network in the hybrid sol when compared to those obtained from coatings generated by external addition of acrylic surface modified silica nanoparticles. The difference in properties was attributed to the level of interaction between the nanoparticles and hybrid sol–gel matrix.     

Submicrometer characterization of surfaces of epoxy‐based organic–inorganic nanocomposite coatings. A comparison of AFM study with currently used testing techniques

Surface properties (morphology, hardness) of transparent colorless epoxy‐based organic–inorganic nanocomposite coatings were investigated by atomic force microscopy, optical and scanning electron microscopy, nanoindentation, and the Persoz pendulum test. Friction and wear coefficients were obtained from tribological experiments. The influence of mechanical properties and the size, shape, and concentration of additives (colloidal silica particles and montmorillonite sheets) on the measured surface characteristics are discussed. It was found that the highest surface hardness (assigned by nanoindentation, pendulum test or expressed as the scratch resistance) exhibited materials with the glass‐transition temperature close to 20°C. Microcopy techniques revealed that surface morphology is influenced by both types of admixtures: on the nanometer scale by colloidal silica particles and on micrometer scale by montmorillonite platelets. Already 1 wt % of montmorillonite increased friction coefficients and wear resistance without distinctive changes of tensile properties. However, the addition of ? 20 wt. % of silica nanoparticles was necessary for the increase of wear and scratch resistances. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5763–5774, 2006     

Subsurface mechanical properties of polyurethane/organoclay nanocomposite thin films studied by nanoindentation

A series of the exfoliated or intercalated PU/organoclay nanocomposite thin films were prepared by in situ polymerization of polyol/organoclay mixture, chain extender and diisocyanate. The surface mechanical properties of the PU/organoclay nanocomposite films were investigated by means of nanoindentation. The results show that the hardness, elastic modulus and scratch resistant of the nanocomposites dramatically improved with the incorporation of organoclay. This improvement was dependent on the clay content as well as the formation structure of clay in the PU matrix. At 3% clay content, the hardness and elastic modulus of intercalated nanocomposites increased by approximately 16% and 44%, respectively, compare to pure PU. For exfoliated nanocomposite, the improvements in these properties were about 3.5 and 1.6 times higher than the intercalated ones. The exfoliated PU nanocomposites also had greater hardness and showed better scratch resistance compared to the intercalated ones.     

Mechanical properties and adhesion of TiN monolayer and TiN/TiAlN nanolayer coatings

In this work, TiN monolayer and TiN/TiAlN nanolayer coatings were deposited on 100C6 (AISI 52100) steel substrate by Physical vapor deposited (PVD) magnetron sputtering system. The morphological characterization was evaluated using an atomic force microscopy. The mechanical properties were determined by nanoindentation test. The adhesion was investigated by both microindentation and scratch test. The results show that the TiN/TiAlN nanolayer coating have the more rough surface and the better mechanical properties and adhesion compared to TiN monolayer coating. The effect of microstructural and mechanical proprieties on the adhesion behavior was further discussed. It was found that the improvement in adhesion of nanolayer system is in part due to the increase in plastic deformation resistance and the enhancement of mechanical properties (hardness and elastic modulus) and to the structure with a small grain size and a high number of interfaces.     

Microstructure and properties of polyester-based polyurethane/titania hybrid films prepared by sol-gel process

Polyester polyol/titania hybrid resins and their corresponding polyurethane/titania hybrid films were prepared by in situ method via sol-gel process of titanium n-butoxide under acidic condition. The effects of the contents and types of titania sol on the microstructure and some mechanical and optical properties of the hybrids were investigated. It was found that introducing titania into the resin could increase some physical properties such as the viscosity of the resin, modulus, T_g, mechanical strength, abrasion resistance, hardness and UV absorbance, but different titania sols obtained from various molar ratios of water to titanium n-butoxide had an obvious influence on the microstructure and properties of the hybrid films.     

Investigations on the mechanical properties of hybrid nanocomposite hard coatings on polycarbonate

Hybrid nanocomposite coatings derived from titanium tetraisopropoxide and epoxy or acrylic modified silanes were deposited on polycarbonate (PC) by dip coating employing various withdrawal speeds followed by ultraviolet and thermal curing. The effect of different organic functional groups in the precursors and ageing effect of these sols were systematically studied with respect to thickness, abrasion resistance, pencil scratch test, nanoindentation hardness and transmittance. The gels derived from the freshly prepared and aged sols were structurally characterized by FT-IR and TEM analysis. The viscosities of the sols were monitored with time. The change in viscosity is rapid for sol from epoxy modified silane. The thickness of the coatings increases with increase in viscosity in case of both the silane precursors. The scratch as well as abrasion resistance increases as a function of coating thickness. The pencil scratch hardness improves from 2B for the bare PC to a maximum of 3H for the coating obtained from an aged sol derived from epoxy modified silane. Also, the abrasion resistance of the coatings from same sol was maximum as evidenced by a <6% change in haze after 500 cycles, vis-a-vis 40% for the bare PC. The coatings from a freshly prepared sol of acrylic modified silane and titania showed the maximum nanoindentation hardness of 0.52 GPa, when compared to 0.23 GPa for the bare PC.     

TiO2/MPMS-SSO光学保护膜的制备与性能研究

以正硅酸乙酯、钛酸丁酯、甲基丙烯酰氧基倍半硅氧烷(MPMS-SSO)、γ-环氧丙氧丙基三甲氧基硅烷为原料,通过溶胶-凝胶法制备了Si-Ti杂化涂料、甲基丙烯酰氧基倍半硅氧烷(MPMS-SSO)涂料、甲基丙烯酰氧基倍半硅氧烷与钛酸丁酯杂化的MPMS-SSO-Ti涂料,并在PMMA上成膜。用FT-IR、UV-VIS、动态摩擦减重测试和TG/DSC等对薄膜的结构、透光率、机械性能和热性能进行表征,并分析了Si-Ti、MPMS-SSO和MPMS-SSO-Ti 3种涂料对PMMA膜的影响。结果表明:Si-Ti、MPMS-SSO、MPMS-SSO-Ti光学保护膜在保持PMMA基片透光率基本不变的同时,有效地提高了耐磨性;MPMS-SSO薄膜的耐磨效果最好,MPMS-SSO膜次之,Si-Ti膜最次。从表面应力、预滑动摩擦力和动摩擦力3个方面分析有机无机杂化膜耐磨性能,能够有效解释涂覆Si-Ti、MPMS-SSO、MPMS-SSO-Ti涂料耐磨性依次提高的事实。Si-Ti、MPMS-SSO、MPMS-SSO-Ti薄膜热稳定性良好,其中MPMS-SSO-Ti薄膜耐热性最好。分析表明,微观上具有规整网络结构的倍半硅氧烷与TiO2杂化对提高薄膜的耐磨性能和热稳定性起着重要作用。     

“Effect of nano-ZnO particles on the corrosion behavior of alkyd-based waterborne coatings”

A nano-composite was formed by incorporating nano-ZnO in a specially developed alkyd-based waterborne coating to different loading levels. The nano-ZnO based composite coatings were applied on mild steel substrate by dipping. The coated panels were subjected to various test environments like salt-spray, humidity, UV and mechanical tests like scratch and abrasion. The improvement in electrochemical performance and mechanical properties of the composite coatings were evaluated using various analytical techniques. FTIR technique was used to investigate the interaction between nano-ZnO particles and the polymer functionalities. Differential scanning calorimetry (DSC) was done to study the curing behavior of nano-composite coatings. SEM and AFM were used to investigate dispersion of nano-ZnO particles and the changes in the surface behavior of the coatings before and after exposure to the test environment. The result showed that, with increase in the concentration of nano-ZnO there was an improvement in the corrosion resistance, UV resistance and mechanical properties of the coatings indicating the positive effect of addition of nano-ZnO particles in the coatings.     

紫外光固化涂料中活性单体的选择

紫外光(UV)固化涂料是以采用辐射固化技术为特征的环保节能型涂料。固化材料的各组分中,预聚物是光固化树脂的主体,它的性能基本决定了固化后材料的主要性能。重点讨论各类不同丙烯酸酯官能度化合物在紫外光固化涂料中的选用及配合,讨论了它们对涂料表面附着力、硬度、耐磨、耐腐等性能的影响。     

TiO_2/MPMS-SSO光学保护膜的制备与性能研究

以正硅酸乙酯、钛酸丁酯、甲基丙烯酰氧基倍半硅氧烷（MPMS-SSO）、γ-环氧丙氧丙基三甲氧基硅烷为原料,通过溶胶-凝胶法制备了Si-Ti杂化涂料、甲基丙烯酰氧基倍半硅氧烷（MPMS-SSO）涂料、甲基丙烯酰氧基倍半硅氧烷与钛酸丁酯杂化的MPMS-SSO-Ti涂料,并在PMMA上成膜。用FT-IR、UV-VIS、动态摩擦减重测试和TG/DSC等对薄膜的结构、透光率、机械性能和热性能进行表征,并分析了Si-Ti、MPMS-SSO和MPMS-SSO-Ti 3种涂料对PMMA膜的影响。结果表明：Si-Ti、MPMS-SSO、MPMS-SSO-Ti光学保护膜在保持PMMA基片透光率基本不变的同时,有效地提高了耐磨性;MPMS-SSO薄膜的耐磨效果最好,MPMS-SSO膜次之,Si-Ti膜最次。从表面应力、预滑动摩擦力和动摩擦力3个方面分析有机无机杂化膜耐磨性能,能够有效解释涂覆Si-Ti、MPMS-SSO、MPMS-SSO-Ti涂料耐磨性依次提高的事实。Si-Ti、MPMS-SSO、MPMS-SSO-Ti薄膜热稳定性良好,其中MPMS-SSO-Ti薄膜耐热性最好。分析表明,微观上具有规整网络结构的倍半硅氧烷与TiO2杂化对提高薄膜的耐磨性能和热稳定性起着重要作用。     

Development of Scratch- and Abrasion-Resistant Coating Materials Based on Nanoparticles,Cured by Radiation

The aim of this study was to compare the effect of monomers, prepolymers, and nanosilica on the scratch and abrasion resistance of nanocomposite coatings. Ultraviolet (UV) and electron beam (EB) curing were used to cure the nanocomposite coatings. The effect of monomers, prepolymers and nanosilica particles on the viscosity, pendulum hardness, gel content, scratch and abrasion resistance were studied. It was found that the optimum formulation for scratch and abrasion resistance contained 15% Ebecryl 600 epoxy acrylate resin with 30% monomer PETIA and 30% of Aerosil OX-50 nanosilica.     

Preparation of Scratch and Abrasion Resistant Polymeric Nanocomposites by Monomer Grafting onto Nanoparticles, 3. Effect of Filler Particles and Grafting Agents

After modification with different trialkoxysilanes, nano‐sized silica and alumina particles were used as fillers in transparent UV/EB curable acrylates for polymer reinforcement, particularly to attain scratch and abrasion resistant coatings. The acid catalyzed condensation of the organosilanes forms a polysiloxane shell which covers the nanoparticle like a nanocapsule. CP MAS NMR spectroscopy and MALDI‐TOF mass spectrometry proved to be useful for the characterization of the polysiloxane structures. Grafted oligomers with more than 20 monomeric units were observed. Nanoparticles modified by methacroyloxy(propyl)trimethoxysilane and vinyltrimethoxysilane can copolymerize with acrylates. Compared with the pure polymers, these crosslinked polyacrylate nanocomposites, containing up to 35 wt.‐% silica, exhibit markedly improved surface mechanical properties. Promising scratch and abrasion resistance of radiation‐cured nanocomposite materials were also obtained by propyltrimethoxysilane grafting which results in an organophilation of pyrogenic silica. Both colloidal and pyrogenic nano‐sized silica nanopowders were used as fillers in polyacrylate films. The concentration of colloidal SiO₂ in commercial acrylate formulations amounts up to 50 wt.‐%, whereas pyrogenic silica, notwithstanding their surface modification by silanes, results in a thickening effect which limits its content to about 35 wt.‐%. Nevertheless, a comparison showed a distinct improvement in the surface mechanical properties such as haze and diamond microscratch hardness for surface‐modified pyrogenic silica.     

Scratch resistant tough nanocomposite epoxy coatings based on hyperbranched polyesters

Advanced multifunctional coatings were prepared by UV curing of epoxy based formulations containing hyperbranched polymers (HBP) and an epoxy functionalized alkoxysilane additive. The addition of HBP to the UV curable epoxy resin induced an important flexibilization of the glassy epoxy network with an increase in toughness of the cured polymeric coatings. Adding the functionalized alkoxysilane into the UV curable formulations, as inorganic precursor of silica phase, an improvement on surface hardness was obtained without strongly affecting the flexibilization and the toughness achieved by the addition of the HBP additive. The increase on surface hardness was accompanied with an increase in scratch resistance and modulus. Advanced scratch resistant and tough nanocomposite epoxy coatings were obtained by properly selecting the components of the formulation.     

Methods for studying the mechanical and tribological properties of hard and soft coatings with a nano-indenter

This study illustrates the capabilities of a nanoindentation/nanoscratch tester to assess mechanical and tribological properties of coating films. Properties such as hardness, elastic modulus, mar and scratch resistance, and critical force for cracking can be accurately measured. Operation of the Nano-Indenter is described in detail. A scanning probe microscope (SPM) is shown to be a valuable supplement to the Nano-Indenter. Well-characterized thermoset acrylic clearcoats and thermoplastic latex films were studied. For the first time, operating parameters are described for measurement of relatively soft coatings, such as films cast from a latex with a glass transition temperature (T_g) of 8°C. Thus, the method is made available for study of most types of coatings. The method can easily discriminate between coatings with different T_gs and crosslink densities. Once operating parameters are established, it takes about 10 minutes for an indentation test and 10 minutes for a scratch test with the Nano-Indenter, and with further automation this time could be reduced. Each indentation test accurately measures hardness and elastic modulus as a function of depth within the coating, and each scratch test provides additional insight into the material’s behavior. The method is sensitive to small changes in polymer composition and formulation, and results are highly reproducible. Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia, PA.     

Mechanical properties of UV-waterborne varnishes reinforced by cellulose nanocrystals

There are many instances in the literature of nanocellulose-thermoplastic composites, but there are few studies on coatings reinforced by cellulose nanocrystals (CNCs). The overall objective of this research was to develop organic nanoparticles-reinforced UV-water-based coatings for wood applications and to study the effect, mainly on wear properties, of the final composite coatings. CNC was mixed in the varnishes to improve the mechanical properties of the coatings. One of the key aspects in the technology of nanocomposites remains the dispersion of the nanoparticles within the matrix as well as its affinity with the matrix. To quantify the dispersion, efficient methods of characterization are needed in order to reveal the nanosized particles. In this article, a novel characterization method based on atomic force microscopy was employed to characterize such nanocomposite coatings, by measuring surface nanoroughness, which is clearly correlated with quality of dispersion and mechanical properties. CNC was modified by either alkyl quaternary ammonium bromides or acryloyl chloride. The mechanical properties (abrasion and scratch resistances, hardness and adhesion) were analyzed and compared to the reference varnish without nanoparticles. The modified CNC addition in UV-water-based coatings results in an approximately 30–40% increase in wear resistance (abrasion and scratch), without any loss of appearance.     

Effect of nano-Al2O3 particles on the corrosion behavior of alkyd based waterborne coatings

A modification in the alkyd based waterborne coatings was studied with the addition of 0.05%, 0.1%, 0.2%, and 0.3% nano-Al₂O₃. Corrosion performance of the nano-composite coatings were evaluated by applying these nanocomposites on mild steel substrate and exposing them to salt spray, humidity, and accelerated weathering. Mechanical properties were studied by subjecting the coating to scratch and abrasion test. The results showed that, with an increase in the concentration of nano-Al₂O₃ there was an improvement in the corrosion resistance, UV resistance, and mechanical properties of the coatings indicating the positive effect of addition of nano-Al₂O₃ particles in the coatings. Further, the transparency of the coating was not altered, maintaining the optical clarity of the coating.     

Study the effect of nano-alumina particles on physical–mechanical properties of UV cured epoxy acrylate via nano-indentation

In this research, an epoxy acrylate resin was synthesized, and then the resin was used along with different multifunctional acrylate monomers and cured under UV radiation. To investigate the effect of nano-particles on some of the physical and mechanical properties, i.e. scratch, hardness and gloss, of the UV cured resins, a suspension of nano-alumina in tripropyleneglycoldiacrylate (TPGDA) was included in the formulations. The scratch resistance was determined by pencil hardness test and nano-scratch tester (NST). The hardness of prepared films was evaluated by using konig hardness tester and nano-indenter.     

Nanoindentation as an alternative to mechanical abrasion for assessing wear of polymeric automotive coatings

Mechanical abrasion followed by transmission delta-haze measurement is a standard means to assess wear in polymeric silicone automotive hard coatings. However, the drawbacks of this abrasion–transmission (A–T) technique (drift, variability, sample size, and test time) make an alternative measurement method desirable. Literature reports have shown that the ratio of hardness to modulus can successfully predict wear performance in ceramic and metallic nanocomposite coatings. This work studied measures from both nanoindentation and nanoscratch testing to determine which could be a viable alternative to the historical A–T test for a specific polymeric coating system. Both nanoindentation measures of hardness (H) and the ratio of hardness to modulus (H/E _r) showed high repeatability compared with the other measures evaluated in this study and compared with the historical test. Of these two measures, the ratio H/E _r with an exponential fit showed the strongest correlation with A–T delta-haze measurements. Key formulation and process factors affecting abrasion resistance in automotive coatings were analyzed in a designed experiment with historical A–T delta-haze and nanoindentation H/E _r as responses. Analysis showed significant benefits to the use of the H/E _r measure of abrasion resistance in modeling coating performance.