Halloysite Nanotubes loaded with Calcium ... - ACS Publications

Subscriber access provided by University of Sussex Library

Applications of Polymer, Composite, and Coating Materials

Halloysite Nanotubes loaded with Calcium Hydroxyde: Alkaline Fillers for the Deacidification of Waterlogged Archeological Woods Giuseppe Cavallaro, Stefana Milioto, Filippo Parisi, and Giuseppe Lazzara ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b09416 • Publication Date (Web): 20 Jul 2018 Downloaded from http://pubs.acs.org on July 22, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Halloysite Nanotubes loaded with Calcium Hydroxyde: Alkaline Fillers for the Deacidification of Waterlogged Archeological Woods Giuseppe Cavallaro*, Stefana Milioto, Filippo Parisi, Giuseppe Lazzara Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, Viale delle Scienze, pad. 17, 90128 Palermo, Italy. E-mail:[email protected]

KEY WORDS. Halloysite, nanotubes, PEG, Waterlogged Archaeological Woods, Deacidification, Long-term protection.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

Abstract A novel green protocol for the decidifying consolidation of waterlogged archaeological woods through aqueous dispersions of polyethylene glycol (PEG) 1500 and halloysite nanotubes containing calcium hydroxide have been designed. Firstly, we prepared the functionalized halloysite filled with Ca(OH)2 in their lumen. The controlled and sustained release of Ca(OH)2 from the halloysite lumen extended its neutralization action over time allowing to develop a longterm deacidfication of the wood samples. A preliminary thermo-mechanical characterization of the clay/polymer nanocomposites allows us to determine the experimental conditions to maximize the consolidation efficiency of the wood samples. The penetration of the halloysite-Ca(OH)2/PEG composite within the wooden pores conferred robustness on the archaeological woods on dependence of the clay/polymer composition of the consolidant mixture. Compared to the archeological wood treated with pure PEG 1500, the addition of the modified nanotubes in the consolidant induced a remarkable improvement of the mechanical performances in terms of flexural strength and rigidity. The pH measurements of the treated woods showed that halloysiteCa(OH)2 are effective alkaline fillers. Accordingly, the modified nanotubes provided a long-term protection for the lignin of the woods exposed to artificial aging under acidic atmosphere. The attained knowledge shows that an easy and green protocol for the long-term preservation of wooden art-works can be achieved by the combination of PEG polymers and alkaline tubular nanostructures obtained through the confinement of Ca(OH)2 within the halloysite cavity

2


Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction

In recent years, innovative technologies have been developed for the conservation of cultural heritages including paintings,1 relics2 and lignocellulosic art-works.3 Within this, inorganic nanoparticles have been proposed as efficient fillers for the consolidation and preservation of paper documents4–6 and archaeological woods.3,7,8 Alkaline nanoparticles were extensively investigated as protective agents of wooden structures and paper, which are mostly deteriorated by the acidic degradation of lignin and lignocellulosic polysaccharides.9–11 Literature reports that nanoparticles of calcium and magnesium hydroxides are suitable deacidifying fillers for waterlogged archaeological woods7 and cellulose-based works.4,6,12 Typically, non-aqueous dispersions of Ca(OH)2 nanoparticles are employed as consolidant systems for ligno-cellulosic materials6,13 As evidenced in our previous work,14 the entrapment of calcium hydroxide within halloysite clay nanotubes (HNTs) generated tubular nanoparticles with an alkaline reservoir that is effective in the long-term protection of paper aged under acidic conditions. Aqueous dispersions of HNTs-Ca(OH)2 hybrid and hydroxypropylcellulose revealed as efficient impregnating systems to preserve the mechanical resistance of paper based documents during the aging.14 It should be noted that the penetration of tubular nanoparticles within the fibrous structure generates significant improvements of both the tensile properties and the thermal stability of paper documents.14 The consolidation of waterlogged archaeological woods is aimed to reduce their high porosity degree, which induces the relevant worsening of their mechanical performance.15 Accordingly, the filling of the wood pores represents the crucial step in the conservation of archaeological wooden structures. Within this, a successful consolidation of archaeological woods was achieved by using sustainable polymers including colophonies,3,16 poly(ethylene) glycols,17–20 beeswax21 and cellulose ethers.22 Recent literature3,21,23 highlighted that the combination of polymers with inorganic nanofiller represents an effective strategy for the consolidation of archaeological woods. It is reported that the polymer adhesion to both the nanoparticles surfaces and the wooden cell walls 3



Page 4 of 34

favours the consolidation.18 As examples, HNTs/esterified colophony8 and HNTs/beeswax21 showed improved consolidation efficiencies with respect to those of pure polymers indicating that a synergetic effect occurs during the impregnation with the composite mixtures. Among the ecocompatible polymers, poly(ethylene) glycols with variable molecular weights represent the most common consolidants for waterlogged archaeological woods from ancient shipwrecks, such as the Vasa (Sweden)7,24,25 and the Batavia (Western Australia).26,27 Notwithstanding, literature7 reports that the impregnation with PEG polymers favours the development of acidity inside the wooden structure enhancing its deterioration. In particular, the degradation of the end groups of poly(ethylene glycol) produces formic acid into the archaeological wood. Additionally, the degradation of ligno-cellulosic polysaccharides is facilitated by the interactions between PEGs and iron species.7 On this basis, deacidifying treatments should be carried out on the archaeological woods consolidated with PEGs in order to preserve their structural and mechanical characteristics. The immersion in soda solution7,28 as well as the application of Ca(OH)2 nanoparticles6,7 are successful in preventing the acidic deterioration of archaeological woods. In particular, the use of Ca(OH)2 is considered strategic as it can form a basic reservoir due to the carbonatation to CaCO3, which ensures the long-term protection as well as non-aggressive basic pH values. Here, we propose an innovative procedure for the deacidification of PEG treated archaeological woods by using HNTs-Ca(OH)2 as additive nanofillers. Due to their morphological and surface characteristics,7,28 halloysite nanotubes are suitable for the filling of the pores of waterlogged archaeological woods. Typically, the length of halloysite is about 1000 nm, while the external and internal diameters range between 20 and 200 and 10–70 nm, respectively.30 It should be noted the both the sizes polydispersity and the specific surface of HNTs depend on their geological deposit.30 Interestingly, the micro-porosity of halloysite can be controlled by acid, neutral, and base treatment.31 According to their geometrical properties, HNTs revealed successful as catalytic supports32–35 and adsorbent nanomaterials for wastewater decontamination.36–39 Several studies highlighted that the halloysite cavity is efficient in the loading and controlled release of chemically 4


Page 5 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and biologically active molecules, such as anticorrosive compounds,40,41 antioxidants,42,43 antiacids14 and biocides.44–46 Functional composite nanomaterials with a sustained activity were obtained by adding modified HNTs within a polymer matrix46–53 In addition, HNTs can be employed as drug delivery systems54–56 and excipients57 for specific biomedical and pharmaceutical applications according to their biocompatibility and low toxicity, which was demonstrated by in vitro and in vivo studies.58,59 In this paper, we employed aqueous dispersions of PEG 1500 and HNTs containing Ca(OH)2 confined into their lumen as consolidants for wooden structures. This formulation is perspective as anti-acid system for waterlogged archaeological woods. The combination of the polymer and the modified clay nanotubes revealed as an efficient and ecocompatible strategy in the long-term preservation of archaeological wood samples. In conclusion, this paper opens a new route for the deacidifying consolidation of wooden structures through green resources.

5



Page 6 of 34

2. Experimental 2.1. Materials Polyethylene Glycol (PEG) 1500, and Ca(OH)2 are from Sigma Aldrich. Halloysite nanotubes (HNTs) from Matauri Bay source (New Zealand) are Imerys Ceramics product. The waterlogged archaeological woods are from the ship Chretienne C, (II century, BC), discovered over the coast of Provence and kindly provided by Prof. Patrice Pomey of C.N.R.S., Université de Provence (France). Based on the procedure of the Italian standard (UNI 11205:2007), the archaeological woods were identified as Pinus Pinaster.60

2.2. Encapsulation of Ca(OH)2 within the halloysite cavity The encapsulation of Ca(OH)2 within the halloysite cavity was achieved by using a method reported in our previous work.14 Briefly, a degassed aqueous solution of Ca(OH)2 (1.5 g·dm−3) was mixed with HNTs powder (5 g·dm−3) and sonicated for 15 min. Then, the Ca(OH)2/HNTs dispersion was magnetically stirred overnight and kept under vacuum for 5 min. This procedure was repeated three times to maximize the amount of Ca(OH)2 loaded onto HNTs. Finally, the solid material was separated from the aqueous phase by centrifugation and dried under vacuum at 70 °C overnight.

2.3 Preparation of nanocomposites based on PEG 1500 and Ca(OH)2/HNTs The HNTs-Ca(OH)2/PEG nanocomposites were prepared by means of the aqueous casting method. Firstly, we prepared a 70 wt% PEG solution in water under stirring for 2 hours at 25 °C. Then, appropriate amounts of HNTs-Ca(OH)2 were added to the PEG solution and kept under stirring. The HNTs-Ca(OH)2/PEG dispersions were poured into Petri dishes at 25 °C to evaporate the solvent until the weight was constant. The HNTs-Ca(OH)2/PEG weight ratio (RH/P) was systematically changed within a wide range. The stoichiometric compositions of the nanocomposites are reported in Supporting Information (Table S1). 6


Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.3. Consolidation of waterlogged archaeological wood The HNTs-Ca(OH)2/PEG composites were employed as consolidants of waterlogged archaeological wood using the immersion method in water. To this purpose, the archaeological wood samples were immersed under stirring in HNTs-Ca(OH)2/PEG aqueous mixtures for three days. The composition of the mixtures was systematically changed by adding variable amounts of HNTs-Ca(OH)2 into PEG aqueous solution (70 wt%). The consolidation efficiency of the archaeological woods was estimated by gravimetric measurements. It should be noted that the HNTs-Ca(OH)2/PEG ratios in the aqueous consolidant mixtures correspond to those of the nanocomposites. As showed by the optical photos (Figure 1), the consolidated wood samples exhibited robustness and mechanical resistance from the macroscopic view point.

Figure 1. Optical photos of the wood sample consolidated by HNTs-Ca(OH)2/PEG (RH/P = 0.22). A mass object of 100 g is placed on the top of the archaeological wood in perpendicular (left) and parallel (right) directions to the wooden channels. The scale bar is 500 mm.

2.4. Wood aging under acidic/oxidative conditions

7



Page 8 of 34

Specimens of both untreated and treated woods were placed in a closed desiccator saturated with nitric acid vapors at 25 °C. Specifically, the desiccator contained a Becher with HNO3 solution (15 vol%) that guaranteed the saturation of the vapors. The aging time was fixed at three days. Prior to testing, all aged wood samples were re-equilibrated with ambient air for 30 days.

2.5 Methods 2.5.1 Thermogravimetry Thermogravimetry (TG) measurements were performed by means of a Q5000 IR apparatus (TA Instruments) under the nitrogen flow of 25 cm3 min-1 for the sample and 10 cm3 min-1 for the balance. The weight of each sample was ca. 5 mg. The experiments were carried out by heating the sample from room temperature to 900 °C with a rate of 20 °C min-1. The temperature calibration was carried out by means of the Curie temperatures of standards (nickel, cobalt, and their alloys).61

2.5.2 Differential scanning calorimetry (DSC) The experiments were conducted by using the differential scanning calorimeter TA Instrument DSC (2920 CE). The calorimeter was calibrated using the melting enthalpy of standard indium (28.71 J g−1). Each sample (ca. 3 mg) was heated according to a temperature program of 20 °C min1

in the temperature range comprised between -20 and 120 °C. The measurements were performed

under a nitrogen flow rate of 60 cm3 min−1.

2.5.3 Scanning electron microscopy (SEM) and elemental analysis The surface morphology of the consolidated wood samples was investigated using a microscope ESEM FEI QUANTA 200F coupled with energy dispersive X-ray spectrometry (EDX) that endows to the elemental analysis. Before each experiment, the surface of the sample was coated with gold in argon by means of an Edwards Sputter Coater S150A to avoid charging under electron beam.

8


Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The measurements were carried out in high vacuum mode (< 6 × 10-4 Pa) for simultaneous secondary electron; the energy of the beam was 25 kV and the working distance was 10 mm.

2.5.4 Dynamic mechanical analysis (DMA) Dynamic mechanical measurements were performed by using the DMA Q800 (TA Instruments). The viscoelastic properties of PEG/HNTs-Ca(OH)2 nanocomposites were investigated through DMA tests in the oscillatory regime (frequency of 1.0 Hz). The strain amplitude was set at 0.5 %. These experiments were carried out at variable temperature by heating the sample from 25 °C to 75 °C with a rate of 4 °C min−1. As concerns the consolidated archaeological woods, we performed three-point flexural measurements at 25 °C. The stress ramp was set at 1 MPa min-1. The force was applied perpendicular to the wood fibers. These experiments were performed on wood samples kept in ambient air for 1 month. The archaeological wood treated by the consolidant mixture with RH/P = 0.22 was tested also after its exposure in ambient air for 15 months in order to investigate the effect of aging on its mechanical performances. The analysis of the stress vs strain curves allowed us to determine the mechanical performance of the treated wood samples in terms of stress and the elongation at the breaking point as well as rigidity, which was estimated by the elastic modulus. The latter was calculated by the slope of stress vs strain functions in the linear region.

2.5.5 Fourier transform infrared (FTIR) spectroscopy Fourier transform infrared (FTIR) spectra were determined at room temperature in the range between 500 and 4000 cm−1 using a Frontier FTIR spectrometer (PerkinElmer). The spectral resolution was 2 cm–1. Each sample was prepared with KBr.

9



Page 10 of 34

2.5.6 pH measurements The pH values of untreated and treated woods were measured by using a HI 1413B/50 portable pH meter with a flat-tip electrode (Hanna Instruments, Milan, Italy). These measurements were performed on archaeological wood samples kept in ambient air for 1, 6 and 12 months.

10


Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3. Results and discussion 3.1 HNTs-Ca(OH)2 as alkaline nanoreservoir The loading of Ca(OH)2 onto the halloysite was aimed to fabricate a tubular nanoreservoir containing an alkaline compound within its lumen. Accordingly, HNTs-Ca(OH)2 might act as deacidiyfing filler for art-works including waterlogged archaeological woods. Moreover, the encapsulation within the HNTs lumen drives to control the Ca(OH)2 release allowing to extend the long-term protection under acidic conditions. Thermogravimetric analyses allowed to estimate that the loading amount of Ca(OH)2 is 4.1 wt%, which is similar to that reported in literature for halloysite provided from a different geological deposit (Dragon Mine).14

3.2 HNTs-Ca(OH)2/PEG nanocomposites: thermal and viscoelastic properties A preliminary characterization of HNTs-Ca(OH)2/PEG nanocomposites was carried out with the aim to evaluate their suitability as consolidants of waterlogged archaeological woods. Figure 2 displays the thermogravimetric curves of pure PEG 1500 and nanocomposites with variable HNTsCa(OH)2 content.

11



Page 12 of 34

Figure 2. TG (a) and DSC (b) curves for PEG 1500 (red solid line), HNTs-Ca(OH)2/PEG at RH/P = 0.11 (blue dotted line) and HNTs-Ca(OH)2/PEG at RH/P = 0.22 (green dashed line). We observed that the presence of nanotubes slightly affects the polymer thermal degradation, which corresponds to the mass loss in the temperature range between 250 and 450 °C (Figure 2a). Above the PEG 1500 degradation, the residual masses of the nanocomposites were shifted to larger values respect to that of pure polymer (Figure 2a) as a consequence of the inorganic filler dispersed into the polymeric matrix. Based on the rule of mixtures,8 we estimated the amount of HNTsCa(OH)2 filled into PEG 1500 by combining the residual masses at 800 °C (MR800) with the mass losses up to 150 °C (ML150), which is due to the physically adsorbed water.8 As a general result, we 12


Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


observed that the experimental concentrations of HNTs-Ca(OH)2 are similar to the stoichiometric ones (see Table S1 in Supporting Information) highlighting that the aqueous casting method was efficient to obtain composite systems with nanotubes homogeneously dispersed into PEG 1500. Similar results were observed for composite systems based on HNTs and esterified colophony.8 As evidenced by DSC thermograms (Figure 2b), the presence of HNTs-Ca(OH)2 affects the PEG 1500 melting process that is represented by the endothermic signal occurring in the temperature range between 30 and 60 °C. Figure 3 shows that the filler addition generated a slight decrease of the melting temperature (determined from the minimum of the DSC peak) as well as a reduction of the enthalpy change, which was calculated through the integration of the DSC endothermic signal.

Figure 3. Temperature (a) and enthalpy change (b) for the PEG 1500 melting as functions of the HNTs-Ca(OH)2/PEG weight ratio.

13



Page 14 of 34

These results highlighted that the interactions between PEG 1500 and HNTs-Ca(OH)2 in the nanocomposite reduce the polymer crystallinity. Namely, the fraction of polymer interacting with HNTs-Ca(OH)2 cannot melt as a consequence of its constraints due to the adsorption onto the nanotubes’ surface. Besides the thermal characterization, the influence of HNTs-Ca(OH)2 on the PEG 1500 melting was investigated through DMA measurements in oscillatory regime, which provided the viscoelastic response of the materials to the temperature. As example, Figure 4a reports the dependence of both storage (G’) and loss (G’’) modulus on the temperature for the nanocomposite with RH/P = 0.024.

14


Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (a) Storage modulus (solid line) and loss modulus (broken line) as functions of temperature for the HNTs-Ca(OH)2/PEG nanocomposite with RH/P= 0.024. (b) Effect of the HNTsCa(OH)2/PEG weight ratio on the inflection temperature of the storage (G’) modulus. We observed that the storage modulus shows a decreasing trend within the temperature interval 3070 °C indicating a reduction of the elastic component induced by the polymer melting. The latter was confirmed by the corresponding increase of tanδ (the ratio between the loss and the storage modulus), which highlighted that the viscous part is predominant during the PEG 1500 melting (see Figure S1 in Supporting Information). Interestingly, the onset temperature for the decrease of the storage modulus was enhanced by the filler addition (Figure 4b). On this basis, we can assert that 15



Page 16 of 34

the PEG 1500 viscoelastic transition (from solid-like material to liquid-like material) was postponed to higher temperatures by the polymer filling with the loaded nanotubes. Namely, the nanocomposites preserved the mechanical properties typical of the solid-like material in a temperature range wider than that of pristine PEG 1500. Accordingly, the HNTs-Ca(OH)2 addition enhanced the capacity of PEG 1500 to store energy during mechanical stress. Similar results were observed for HNTs/beeswax nanocomposites.21 The viscoelasctic behavior of HNTs-Ca(OH)2/PEG composite mixtures is promising for their use as consolidants of waterlogged archaeological woods.

3.3 Treatment of archaeological woods by HNTs-Ca(OH)2/PEG aqueous mixtures Aqueous composite mixtures based on PEG 1500 and HNTs-Ca(OH)2 were investigated as consolidants of waterlogged archaeological woods using the immersion procedure previously described for acetone dispersions of HNTs/beeswax21 and HNTs/esterified colophony.8 Contrary to our previous studies,3,21 the proposed consolidation protocol can be considered totally environmentally safe being that water was used as immersion solvent for the wood impregnation. The combination of PEG 1500 and HNTs loaded with Ca(OH)2 was explored to generate a hybrid consolidant with synergetic functionalities allowing to 1) confer mechanical resistance to the treated wood; 2) control the pH of the wood surface; 3) provide a long-term protection to the wood aged under acidic/oxidative atmosphere.

3.2.1 Consolidation efficacy The total amount of consolidant entrapped within the wooden structure was determined through gravimetric measurements. As shown in Figure 5a, the consolidant/wood weight ratio (RC/W) in the treated wood increased with the nanotubes’ concentration of the HNTs-Ca(OH)2/PEG mixture highlighting an improvement of the consolidation efficiency. Details on the calculation of RC/W are presented in Supporting Information. 16


Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. The consolidant/wood weight ratio (a) and the filling efficiency (b) as fucntions of the HNTs-Ca(OH)2/PEG weight ratio of the composite mixture. In addition, we determined the percent of the filled wood pores (F%) as F% = 100 · (RC/W /R*C/W)

(1)

where R*c/w is the theoretical consolidant/wood weight ratio if the wooden pores are fully filled by the composite consolidant. Based on the maximum water content (MWC) of the pure archeological wood (see details on the calculation in Supporting Information), the R*C/W values were calculated as R*C/W= MWC · δcons

(2)

17



Page 18 of 34

being δcons the consolidant density. The MWC value for the investigated wood is 81.3 wt%. Assuming that the penetration of the consolidant within the wood structure does not alter the composition of the composite, δcons was estimated by the rule of mixtures taking into account the densities of the pure components (PEG1500 and HNTs-Ca(OH)2) as well as the PEG1500/HNTsCa(OH)2 ratio of the mixtures employed in the consolidation of the archaeological wood samples. Supporting Information (Table S2) reports the δcons values for the consolidant mixtures and pure components. Figure 5b shows that F% linearly increased with the HNTs-Ca(OH)2 concentration highlighting that the presence of nanotubes in the consolidant significantly enhances the filling efficiency of the wood pores. A fulfillment of the wooden structure was achieved for composite consolidant with RH/P ≥ 0.11. The consolidation efficiency determined from the gravimetric approach was correlated to the FT-IR data, which allowed us to discriminate the amounts of PEG1500 and HNTs-Ca(OH)2 entrapped within the wooden structure. The characteristic bands of lignin were observed in both untreated and treated archaeological woods. In this regards, Figure 6a shows the peak at 1511 cm-1 that is related to the skeletal vibrations of the aromatic ring of lignin.24,62

Figure 6. FT-IR spectra of untreated and treated wood samples in the wavelength ranges 14901515 cm-1 (a) and 800-900 cm-1 (b). 18


Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Compared to the pristine archaeological wood, the intensity of the peak at 1511 cm-1 (I1511 cm-1) was reduced in the treated samples according to the filling of the wooden structure by the consolidants. The presence of HNTs-Ca(OH)2 in the consolidated woods was proved by the peaks at 3620 and 3700 cm-1 (see Figure S2 in Supporting Information), which are attributed to the OH stretching vibrations of the Al-OH groups of halloysite. On the other hand, the successful entrapment of PEG 1500 into the wood was evidenced by the band at 842 cm-1 (Figure 6b) that is related to the symmetrical C-O-C stretching of polyethylene glycols.24 Accordingly, this signal was not detected in the untreated wood sample (Figure 6b). The intensities of the peaks at 842 cm-1 (I842 cm-1) and 1511 cm-1 (I1511 cm-1) in the consolidated wood samples allowed to determine the amounts of PEG 1500 and HNTs-Ca(OH)2 filled into the wooden structure by using the approach described as follows. Concerning the wood consolidated with pure PEG 1500, the (I842 cm-1)/(I1511 cm-1) ratio can be strictly correlated to the experimental RC/W value determined from the gravimetric method. Being R0C/W the consolidant/wood weight ratio for the sample treated with the neat polymer, a correlation coefficient between the PEG 1500/wood weight ratio (RP/W) and the IR intensity peaks can be determined. On this basis, the RP/W values of the wood samples consolidated with the composite mixtures were determined as

RP/W = [(I842 cm-1)/(I1511 cm-1)]H-P-W · [(R0C/W /((I842 cm-1)/(I1511 cm-1)) P-W]

where the subscripts

P-W

and

H-P-W

(3)

refer to the wood samples treated with pure PEG 1500 and

PEG/HNTs-Ca(OH)2 composite, respectively. For all the treated samples, the HNTs-Ca(OH)2/wood weight ratio (RH/W) can be expressed as

RH/W = RC/W - RP/W

(4)

19



Page 20 of 34

It should be noted that the RH/W values cannot be calculated by considering the characteristic bands of halloysite because the wood consolidation with pure HNTs-Ca(OH)2 was not carried out. As shown in Figure 7, both RP/W and RH/W are affected by the HNTs-Ca(OH)2/PEG ratio in the impregnating aqueous mixture. For RH/P ≤ 0.056 the addition of the loaded nanotubes favored the penetration of PEG 1500 into the wood as evidenced by the increase of RP/W (Figure 7a). On the contrary, a larger HNTs-Ca(OH)2 content induced a RP/W reduction because the wood pores are largely filled by the nanotubes. Accordingly, RH/W shows an increasing trend with RH/P in the all investigated range (Figure 7b). Similar results were observed for archaeological woods consolidated with acetone mixtures of esterified colophony and halloysite.8

20


Page 21 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. The PEG/wood (a) and HNTs-Ca(OH)2/wood (b) weight ratios (determined from IR spectra) as functions of the HNTs-Ca(OH)2/PEG weight ratio of the consolidation mixture.

A better understanding of the consolidation process was achieved by determining the composition of the composite penetrated into the wood, In particular, the weight fractions of PEG 1500 (χP) and HNTs-Ca(OH)2 (χH) were determined as RP/W/RC/W and RH/W/RC/W, respectively. The obtained results were compared with the stoichiometric composition of the HNTs-Ca(OH)2/PEG composite employed in the consolidation procedure (see Table S1 in Supporting Information) highlighting that the penetration into the wood altered the HNTs-Ca(OH)2/PEG ratio of the hybrid consolidant. On this basis, the filling efficiencies expressed by the F% values were re-calculated (see equations 1,2) taking into account the experimental HNTs-Ca(OH)2/PEG composition of the composite penetrated into the wood. As highlighted in Table 1, a reasonable agreement between the F% values from FTIR data and gravimetric measurements was observed.

Table 1. Percent of wood pores filled by the consolidants. HNTs-Ca(OH)2/PEG ratio (in the impregnating solution)

Percent of filled pores (from FT-IR spectra)

0

Percent of filled pores (from gravimetric measurements) 58.5 ± 0.5

0.011

71.7 ± 0.6

70.7 ± 0.7

0.056

93.7 ± 0.8

93.6 ± 0.9

0.11

98.7 ± 0.8

97.7 ± 1.0

0.22

99.1 ± 0.8

98.8 ± 1.0

58.5 ± 0.5

3.2.2 Morphology and mechanical performances of the consolidated woods

Figure 8 displays SEM images of the archaeological wood treated with the HNTs-Ca(OH)2/PEG composite (RH/P = 0.22). The micrographs at low magnification (Figures 8a,b) showed the 21



Page 22 of 34

characteristic channels of the archaeological woods. The empty space of the wood channels was filled by the HNTs-Ca(OH)2/PEG hybrid in agreement with the successful consolidation. As evidenced by SEM images at high magnification (Figures 8c,d), the nanotubes are embedded within the polymer matrix ruling out any separation processes between HNTs-Ca(OH)2 and PEG 1500 during the consolidation procedure. Interestingly, EDX spectrum (Figure 8e) revealed the presence of Ca in the consolidated wood. This result highlighted that the loading of Ca(OH)2 onto the nanotubes was preserved in the composite consolidant, which possesses an alkaline reservoir useful for deacidification and long-term protection of the treated woods. The quantitative analysis of the EDX spectrum is presented in Supporting Information (Table S3). The Al/Si atomic ratio is consistent with the stoichiometric composition of halloyiste, while the presence of carbon can be attributed to both the wood and the polymer. It should be noted that the Au peak in the EDX spectrum is due to the deposition of gold on the sample surface.

Figure 8. SEM images at different magnification (a,b,c,d) and EDX spectrum (e) for wood treated with HNTs-Ca(OH)2/PEG (RH/P = 0.22). The successful consolidation of HNTs-Ca(OH)2/PEG composite induced a significant enhancement of the mechanical performances of the archaeological wood. It should be noted that the untreated 22


Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


wood sample was not tested by flexural experiments because of its high fragility. Some examples of stress vs strain curves for consolidated woods are presented in Figure 9a.

Figure 9. Stress vs strain curves for consolidated wood samples (a). The dependence of the elastic modulus (b) and the stress at breaking point (c) on the HNTs-Ca(OH)2/PEG ratio of the consolidation mixture.

23



Page 24 of 34

We observed that both the elastic modulus and the stress at the breaking point show an increasing trend with the RH/P of the consolidant mixtures (Figure 9b,c). These results can be attributed to the increase of the consolidation efficiency detected in the composite consolidants (Figure 5) as well as to the filling of the wooden channels by the nanotubes. Compared to the treatment with pure polymer, the consolidation by the HNTs-Ca(OH)2/PEG mixtures generated a strong improvement of the wood stiffness as evidenced by the larger elastic modulus. In this regards, the elastic modulus of the wood treated by HNTs-Ca(OH)2/PEG composite showed a reliable increase (up to one order) with respect to the sample consolidated by neat PEG 1500. Similarly, a relevant enhancement of the stress at the breaking point was detected by the addition of HNTs-Ca(OH)2 in the consolidation protocol. As example, the stress at the breaking point for the wood treated with HNTsCa(OH)2/PEG at RH/P = 0.22 is ca. 9 times larger respect to that consolidated with pure PEG 1500. Regarding the elongation at the breaking point of the treated woods (see Table S4 in Supporting Information), the consolidant mixtures with RH/P = 0.22 generated a relevant reduction compared to the sample consolidated with pure PEG 1500. Finally, we observed that the mechanical performances of the consolidated archeological woods were not significantly altered by the aging in ambient air. As evidenced in Supporting Information (Table S5), the exposure in air for a longer time (from 1 to 15 months) did not generate a relevant reduction of both the rigidity and the flexural resistance of the wood sample consolidated with HNTs-Ca(OH)2/PEG at RH/P = 0.22.

3.2.3 Influence of consolidants on the pH of wood surface

The efficacy of HNTs-Ca(OH)2 as alkaline nanoreservoirs for the wood protection was estimated by measuring the surface pH of the consolidated samples (Figure 10). The measurements were conducted over time (after 1, 6 and 12 months from the consolidation) in order to investigate the long-term neutralization effect of Ca(OH)2 entrapped into the HNTs lumen.

24


Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 10. The pH of the surface of consolidated wood samples as function of the HNTsCa(OH)2/PEG ratio of the impregnating mixture at different time from the consolidation. We observed that the surface of the wood treated by pure PEG 1500 possesses a slight acidic pH (Figure 10), which could be attributed to the formation of formic acid due to the degradation of the 25



Page 26 of 34

end groups of poly(ethylene glycol).7 Accordingly, we determined that the surface pH of the untreated sample is neutral ruling out that the decomposition of wooden components induced the acidity in the archeological wood consolidated with neat PEG 1500. The addition of loaded nanotubes in the impregnating solution caused a pH enhancement of the consolidated wood samples highlighting the neutralizing action of Ca(OH)2 entrapped into the HNTs cavity. Namely, the alkaline nanofillers neutralizes the acidic species formed by the PEG degradation. As evidenced in Figure 10, the neutralizing effect increases with the HNTs-Ca(OH)2 content of the composite consolidant. The pH data collected after 6 and 12 months from the consolidation showed that the HNTs-Ca(OH)2 provide a long-term deacidification of the treated woods. Regarding the wood treated with the largest HNTs-Ca(OH)2 amount (RH/P = 0.22), the surface pH was significantly increased over time in the first 6 months (7.3 and 8.3 after 1 and 6 months from the consolidation, respectively). The neutralization effect was very efficient even after 12 months from the consolidation being that the pH surface of the treated wood was 7.6. This result can be attributed to the sustained Ca(OH)2 release from the HNTs cavity as demonstrated in our previous work.14 On this basis, the neutralizing action of the filled nanotubes is guaranteed for several months.

3.2.4 Wood aging under acidic conditions: the protection effect of HNTs-Ca(OH)2/PEG The protection efficiency of the consolidants was tested by monitoring the effect on the lignin produced by the exposure of the wood samples to HNO3 saturated vapors, which simulate the aging under acidic conditions. To this purpose, we determined the variation of the lignin index upon aging for untreated and treated woods. As reported elsewhere,62 the lignin index (L.I.) was calculated from the IR spectra by normalising the peak intensities of the lignin group at 1511 cm−1 (I1511 cm-1) with the C-H deformation and CH3 groups at 1375 cm−1 (I1375 cm-1). As a general result, the L.I. value was reduced upon aging as a consequence of the lignin degradation. Accordingly, the relative reduction of the L.I. value (∆L.I.) after the exposure to HNO3 vapors quantitatively the 26


Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


decomposition of the archaeological wood being that lignin is its main component. As expected, ∆L.I. = 99.0 % was estimated for the untreated wood because of the totally degradation of lignin (Figure 11). The presence of the consolidant in the wood structure preserved the lignin as highlighted by the lower ∆L.I. values (Figure 11).

Figure 11. Relative reduction of the lignin index upon aging for treated wood samples.

Figure 11 shows that the wood consolidation with pure PEG 1500 slightly reduced the L.I. variation (∆L.I. = 94.5 %) indicating that the pure polymer did not provide an efficient protection to the wood structure. On the other hand, the addition of HNTs-Ca(OH)2 improved the protection efficacy of the consolidant as evidenced by the lower ∆L.I. values. This effect is mostly due to the loaded Ca(OH)2 that hinders the acidic degradation of lignin. Accordingly, the increase of HNTsCa(OH)2 in the consolidation mixture enhanced the protection capacity towards the treated wood.

27



Page 28 of 34

4. Conclusions Tubular nanoparticles with an alkaline reservoir were obtained by confining Ca(OH)2 within the cavity of halloysite nanotubes (HNTs). The Ca(OH)2-HNTs hybrids were dispersed into polyethylene glycol (PEG) 1500 with the aim to develop a composite deacidifying consolidant for waterlogged archeological woods. A preliminarily investigation of the Ca(OH)2-HNTs/PEG nanocomposites evidenced that the thermal properties (degradation and melting temperatures) of the polymer are slightly affected by the filler addition. On the other hand, viscoelastic measurements highlighted that the presence of Ca(OH)2-HNTs increases the capacity of PEG 1500 to store energy during mechanical stress. This latter result is promising for the consolidation of waterlogged archaeological woods, which were treated through the immersion method by using aqueous Ca(OH)2-HNTs/PEG mixtures. We observed that the clay/polymer ratio affects the consolidation efficiency and, consequently, the improvement of the mechanical performances of the treated woods. The presence of the modified HNTs in the consolidant significantly improved both the flexural strength and rigidity of the treated archeological woods with respect to those detected for the sample consoliated with pure PEG 1500. SEM images of the consolidated samples showed that the wooden channels were successfully filled by the composite consolidant, while the presence of Ca(OH)2 in the wood was evidenced by the corresponding EDX spectrum. The deacidifying action of Ca(OH)2-HNTs was evidenced by the surface pH measurements of the treated wood. Interestingly, this functionality was detected even 1 year after the wood consolidation. According to these results, the impregnation by Ca(OH)2-HNTs/PEG mixtures revealed efficient in the long-term protection of the wooden structures aged under acidic conditions. In particular, the analysis of FT-IR spectra showed that Ca(OH)2-HNTs exhibits a protective role on the lignin of the archaeological woods. In conclusion, this study is encouraging for designing a green protocol for the durable preservation of archaeological woods by means of biocompatible materials including polyethylene glycol and halloysite clay nanotubes containing calcium hydroxide. 28


Page 29 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Acknowledgment The work was financially supported by the University of Palermo, (PON03PE_00214_1). The authors have no conflicts of interest to declare.

PON-TECLA

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Details on the calculation of the consolidant/wood weight ratio (Rc/w) in the treated wood; Details on the determination of the maximum water content (MWC) of the archeological wood; Composition of HNTs-Ca(OH)2/PEG composites; Densities of the consolidant mixtures and the pure components; Quantitative analysis of the EDX spectrum for the wood treated with HNTsCa(OH)2/PEG (RH/P = 0.22); Elongation at breaking point for the treated woods; Effect of aging on the mechanical performances of archaeological wood consolidated by the HNTs-Ca(OH)2/PEG mixture with RH/P = 0.22; Dependence on temperature of tanδ for the HNTs-Ca(OH)2/PEG nanocomposite with RH/P= 0.024; FT-IR spectrum (in the wavelength range 3600-3720 cm-1) of the wood sample treated by HNTs-Ca(OH)2/PEG mixture with RH/P= 0.22.

References (1)

(2)

(3)

(4)

(5)

(6)

(7)

(8) (9)

Banti, D.; La Nasa, J.; Tenorio, A. L.; Modugno, F.; Jan van den Berg, K.; Lee, J.; Ormsby, B.; Burnstock, A.; Bonaduce, I. A Molecular Study of Modern Oil Paintings: Investigating the Role of Dicarboxylic Acids in the Water Sensitivity of Modern Oil Paints. RSC Adv 2018, 8 (11), 6001–6012. Zheng, L. Z.; Liang, X. T.; Li, S. R.; Li, Y. H.; Hu, D. D. Fading and Showing Mechanisms of Ancient Color Relics Based on Light Scattering Induced by Particles. RSC Adv 2018, 8 (2), 1124–1131. Cavallaro, G.; Lazzara, G.; Milioto, S.; Parisi, F.; Ruisi, F. Nanocomposites Based on Esterified Colophony and Halloysite Clay Nanotubes as Consolidants for Waterlogged Archaeological Woods. Cellulose 2017, 24 (8), 3367–3376. Giorgi, R.; Dei, L.; Ceccato, M.; Schettino, C.; Baglioni, P. Nanotechnologies for Conservation of Cultural Heritage: Paper and Canvas Deacidification. Langmuir 2002, 18 (21), 8198–8203. Barhoum, A.; Rahier, H.; Abou-Zaied, R. E.; Rehan, M.; Dufour, T.; Hill, G.; Dufresne, A. Effect of Cationic and Anionic Surfactants on the Application of Calcium Carbonate Nanoparticles in Paper Coating. ACS Appl. Mater. Interfaces 2014, 6 (4), 2734–2744. Poggi, G.; Giorgi, R.; Toccafondi, N.; Katzur, V.; Baglioni, P. Hydroxide Nanoparticles for Deacidification and Concomitant Inhibition of Iron-Gall Ink Corrosion of Paper. Langmuir 2010, 26 (24), 19084–19090. Giorgi, R.; Chelazzi, D.; Baglioni, P. Nanoparticles of Calcium Hydroxide for Wood Conservation. The Deacidification of the Vasa Warship. Langmuir 2005, 21 (23), 10743– 10748. Schofield, E. J.; Sarangi, R.; Mehta, A.; Jones, A. M.; Mosselmans, F. J. W.; Chadwick, A. V. Nanoparticle De-Acidification of the Mary Rose. Mater. Today 2011, 14 (7), 354–358. Rasmussen, H.; Tanner, D.; Sorensen, H. R.; Meyer, A. S. New Degradation Compounds from Lignocellulosic Biomass Pretreatment: Routes for Formation of Potent Oligophenolic Enzyme Inhibitors. Green Chem 2017, 19 (2), 464–473. 29



Page 30 of 34

(10) Dedic, D.; Iversen, T.; Ek, M. Cellulose Degradation in the Vasa: The Role of Acids and Rust. Stud. Conserv. 2013, 58 (4), 308–313. (11) Bugg, T. D.; Ahmad, M.; Hardiman, E. M.; Singh, R. The Emerging Role for Bacteria in Lignin Degradation and Bio-Product Formation. Energy Biotechnol. – Environ. Biotechnol. 2011, 22 (3), 394–400. (12) Dong, C.; Cairney, J.; Sun, Q.; Maddan, O. L.; He, G.; Deng, Y. Investigation of Mg(OH)2 Nanoparticles as an Antibacterial Agent. J. Nanoparticle Res. 2010, 12 (6), 2101–2109. (13) Poggi, G.; Toccafondi, N.; Melita, L. N.; Knowles, J. C.; Bozec, L.; Giorgi, R.; Baglioni, P. Calcium Hydroxide Nanoparticles for the Conservation of Cultural Heritage: New Formulations for the Deacidification of Cellulose-Based Artifacts. Appl. Phys. A 2014, 114 (3), 685–693. (14) Cavallaro, G.; Danilushkina, A. A.; Evtugyn, V. G.; Lazzara, G.; Milioto, S.; Parisi, F.; Rozhina, E. V.; Fakhrullin, R. F. Halloysite Nanotubes: Controlled Access and Release by Smart Gates. Nanomaterials 2017, 7 (8), 199–210. (15) Riggio, M.; Sandak, J.; Sandak, A.; Pauliny, D.; Babiński, L. Analysis and Prediction of Selected Mechanical/Dynamic Properties of Wood after Short and Long-Term Waterlogging. Constr. Build. Mater. 2014, 68, 444–454. (16) Giachi, G.; Capretti, C.; Donato, I. D.; Macchioni, N.; Pizzo, B. New Trials in the Consolidation of Waterlogged Archaeological Wood with Different Acetone-Carried Products. J. Archaeol. Sci. 2011, 38 (11), 2957–2967. (17) Cavallaro, G.; Donato, D. I.; Lazzara, G.; Milioto, S. Determining the Selective Impregnation of Waterlogged Archaeological Woods with Poly(Ethylene) Glycols Mixtures by Differential Scanning Calorimetry. J. Therm. Anal. Calorim. 2013, 111 (2), 1449–1455. (18) Christensen, M.; Kutzke, H.; Hansen, F. K. New Materials Used for the Consolidation of Archaeological Wood–Past Attempts, Present Struggles, and Future Requirements. Wood Sci. Conserv. 2012, 13, S183–S190. (19) Cipriani, G.; Salvini, A.; Fioravanti, M.; Di Giulio, G.; Malavolti, M. Synthesis of Hydroxylated Oligoamides for Their Use in Wood Conservation. J. Appl. Polym. Sci. 2013, 127 (1), 420–431. (20) Meints, T.; Hansmann, C.; Gindl-Altmutter, W. Suitability of Different Variants of Polyethylene Glycol Impregnation for the Dimensional Stabilization of Oak Wood. Polymers 2018, 10 (1), 81–92. (21) Cavallaro, G.; Lazzara, G.; Milioto, S.; Parisi, F.; Sparacino, V. Thermal and Dynamic Mechanical Properties of Beeswax-Halloysite Nanocomposites for Consolidating Waterlogged Archaeological Woods. Polym. Degrad. Stab. 2015, 120, 220–225. (22) Walsh, Z.; Janeček, E.-R.; Jones, M.; Scherman, O. A. Natural Polymers as Alternative Consolidants for the Preservation of Waterlogged Archaeological Wood. Stud. Conserv. 2017, 62 (3), 173–183. (23) Cataldi, A.; Deflorian, F.; Pegoretti, A. Microcrystalline Cellulose Filled Composites for Wooden Artwork Consolidation: Application and Physic-Mechanical Characterization. Mater. Des. 2015, 83, 611–619. (24) Glastrup J.; Shashoua Y.; Egsgaard H.; Mortensen M. Degradation of PEG in the Warship Vasa. Macromol. Symp. 2006, 238 (1), 22–29. (25) Wagner, L.; Almkvist, G.; Bader, T. K.; Bjurhager, I.; Rautkari, L.; Gamstedt, E. K. The Influence of Chemical Degradation and Polyethylene Glycol on Moisture-Dependent Cell Wall Properties of Archeological Wooden Objects: A Case Study of the Vasa Shipwreck. Wood Sci. Technol. 2016, 50 (6), 1103–1123. (26) Hoffmann, P.; Singh, A.; Kim, Y. S.; Wi, S. G.; Kim, I. J.; Schmitt, U. The Bremen Cog of 1380 – An Electron Microscopic Study of Its Degraded Wood before and after Stabilization with PEG. Holzforschung 2004, 58 (3), 211–218. 30


Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(27) Hoffmann, P. On the Long-Term Visco-Elastic Behaviour of Polyethylene Glycol (PEG) Impregnated Archaeological Oak Wood. Holzforschung 2010, 64 (6), 725–728. (28) Sandström, M.; Jalilehvand, F.; Persson, I.; Gelius, U.; Frank, P.; Hall-Roth, I. Deterioration of the Seventeenth-Century Warship Vasa by Internal Formation of Sulphuric Acid. Nature 2002, 415, 893. (29) Lvov, Y.; Wang, W.; Zhang, L.; Fakhrullin, R. Halloysite Clay Nanotubes for Loading and Sustained Release of Functional Compounds. Adv. Mater. 2016, 28 (6), 1227–1250. (30) Pasbakhsh, P.; Churchman, G. J.; Keeling, J. L. Characterisation of Properties of Various Halloysites Relevant to Their Use as Nanotubes and Microfibre Fillers. Appl. Clay Sci. 2013, 74, 47–57. (31) Joo, Y.; Sim, J. H.; Jeon, Y.; Lee, S. U.; Sohn, D. Opening and Blocking the Inner-Pores of Halloysite. Chem. Commun. 2013, 49 (40), 4519–4521. (32) Liu, Y.; Guan, H.; Zhang, J.; Zhao, Y.; Yang, J.-H.; Zhang, B. Polydopamine-Coated Halloysite Nanotubes Supported AgPd Nanoalloy: An Efficient Catalyst for Hydrolysis of Ammonia Borane. Int. J. Hydrog. Energy 2018, 43 (5), 2754–2762. (33) Wang, Q.; Wang, Y.; Zhao, Y.; Zhang, B.; Niu, Y.; Xiang, X.; Chen, R. Fabricating Roughened Surfaces on Halloysite Nanotubes via Alkali Etching for Deposition of HighEfficiency Pt Nanocatalysts. CrystEngComm 2015, 17 (16), 3110–3116. (34) Sadjadi, S.; Hosseinnejad, T.; Malmir, M.; Heravi, M. M. Cu@furfural Imine-Decorated Halloysite as an Efficient Heterogeneous Catalyst for Promoting Ultrasonic-Assisted A3 and KA2 Coupling Reactions: A Combination of Experimental and Computational Study. New J Chem 2017, 41 (22), 13935–13951. (35) Vinokurov, V.; Glotov, A.; Chudakov, Y.; Stavitskaya, A.; Ivanov, E.; Gushchin, P.; Zolotukhina, A.; Maximov, A.; Karakhanov, E.; Lvov, Y. Core/Shell Ruthenium–Halloysite Nanocatalysts for Hydrogenation of Phenol. Ind. Eng. Chem. Res. 2017, 56 (47), 14043– 14052. (36) Zhao, Y.; Abdullayev, E.; Vasiliev, A.; Lvov, Y. Halloysite Nanotubule Clay for Efficient Water Purification. J. Colloid Interface Sci. 2013, 406 (0), 121–129. (37) Cavallaro, G.; Grillo, I.; Gradzielski, M.; Lazzara, G. Structure of Hybrid Materials Based on Halloysite Nanotubes Filled with Anionic Surfactants. J. Phys. Chem. C 2016, 120 (25), 13492–13502. (38) Owoseni, O.; Nyankson, E.; Zhang, Y.; Adams, S. J.; He, J.; McPherson, G. L.; Bose, A.; Gupta, R. B.; John, V. T. Release of Surfactant Cargo from Interfacially-Active Halloysite Clay Nanotubes for Oil Spill Remediation. Langmuir 2014, 30 (45), 13533–13541. (39) Panchal, A.; Swientoniewski, L. T.; Omarova, M.; Yu, T.; Zhang, D.; Blake, D. A.; John, V.; Lvov, Y. M. Bacterial Proliferation on Clay Nanotube Pickering Emulsions for Oil Spill Bioremediation. Colloids Surf. B Biointerfaces 2018, 164, 27–33. (40) Joshi, A.; Abdullayev, E.; Vasiliev, A.; Volkova, O.; Lvov, Y. Interfacial Modification of Clay Nanotubes for the Sustained Release of Corrosion Inhibitors. Langmuir 2013, 29 (24), 7439–7448. (41) Fakhrullin, R. F.; Tursunbayeva, A.; Portnov, V. S.; L’vov, Y. M. Ceramic Nanotubes for Polymer Composites with Stable Anticorrosion Properties. Crystallogr. Rep. 2014, 59 (7), 1107–1113. (42) Zhong, B.; Lin, J.; Liu, M.; Jia, Z.; Luo, Y.; Jia, D.; Liu, F. Preparation of Halloysite Nanotubes Loaded Antioxidant and Its Antioxidative Behaviour in Natural Rubber. Polym. Degrad. Stab. 2017, 141, 19–25. (43) Lvov, Y.; Aerov, A.; Fakhrullin, R. Clay Nanotube Encapsulation for Functional Biocomposites. Adv Colloid Interface Sci 2014, 207 (0), 189–198. (44) Jana, S.; Kondakova, A. V.; Shevchenko, S. N.; Sheval, E. V.; Gonchar, K. A.; Timoshenko, V. Y.; Vasiliev, A. N. Halloysite Nanotubes with Immobilized Silver Nanoparticles for AntiBacterial Application. Colloids Surf. B Biointerfaces 2017, 151, 249–254. 31



Page 32 of 34

(45) Abdullayev, E.; Sakakibara, K.; Okamoto, K.; Wei, W.; Ariga, K.; Lvov, Y. Natural Tubule Clay Template Synthesis of Silver Nanorods for Antibacterial Composite Coating. ACS Appl Mater Interfaces 2011, 3 (10), 4040–4046. (46) Makaremi, M.; Pasbakhsh, P.; Cavallaro, G.; Lazzara, G.; Aw, Y. K.; Lee, S. M.; Milioto, S. Effect of Morphology and Size of Halloysite Nanotubes on Functional Pectin Bionanocomposites for Food Packaging Applications. ACS Appl. Mater. Interfaces 2017, 9 (20), 17476–17488. (47) Gorrasi, G. Dispersion of Halloysite Loaded with Natural Antimicrobials into Pectins: Characterization and Controlled Release Analysis. Carbohydr. Polym. 2015, 127, 47–53. (48) Du, M.; Guo, B.; Jia, D. Newly Emerging Applications of Halloysite Nanotubes: A Review. Polym. Int. 2010, 59 (5), 574–582. (49) Du, M.; Guo, B.; Lei, Y.; Liu, M.; Jia, D. Carboxylated Butadiene–Styrene Rubber/Halloysite Nanotube Nanocomposites: Interfacial Interaction and Performance. Polymer 2008, 49 (22), 4871–4876. (50) Liu, M.; Chang, Y.; Yang, J.; You, Y.; He, R.; Chen, T.; Zhou, C. Functionalized Halloysite Nanotube by Chitosan Grafting for Drug Delivery of Curcumin to Achieve Enhanced Anticancer Efficacy. J Mater Chem B 2016, 4 (13), 2253–2263. (51) Liu, M.; Wu, C.; Jiao, Y.; Xiong, S.; Zhou, C. Chitosan-Halloysite Nanotubes Nanocomposite Scaffolds for Tissue Engineering. J. Mater. Chem. B 2013, 1 (15), 2078– 2089. (52) Tao, D.; Higaki, Y.; Ma, W.; Wu, H.; Shinohara, T.; Yano, T.; Takahara, A. Chain Orientation in Poly(Glycolic Acid)/Halloysite Nanotube Hybrid Electrospun Fibers. Polymer 2015, 60, 284–291. (53) Wei, M.; Yuji, H.; Atsushi, T. Superamphiphobic Coatings from Combination of a Biomimetic Catechol‐Bearing Fluoropolymer and Halloysite Nanotubes. Adv. Mater. Interfaces 4 (23), 1700907. (54) Lvov, Y. M.; DeVilliers, M. M.; Fakhrullin, R. F. The Application of Halloysite Tubule Nanoclay in Drug Delivery. Expert Opin. Drug Deliv. 2016, 13 (7), 977–986. (55) Liu, F.; Bai, L.; Zhang, H.; Song, H.; Hu, L.; Wu, Y.; Ba, X. Smart H2O2-Responsive Drug Delivery System Made by Halloysite Nanotubes and Carbohydrate Polymers. ACS Appl. Mater. Interfaces 2017, 9 (37), 31626–31633. (56) Cavallaro, G.; Lazzara, G.; Milioto, S.; Parisi, F.; Evtugyn, V.; Rozhina, E.; Fakhrullin, R. Nanohydrogel Formation within the Halloysite Lumen for Triggered and Sustained Release. ACS Appl. Mater. Interfaces 2018, 10 (9), 8265–8273. (57) Yendluri, R.; Otto, D. P.; De Villiers, M. M.; Vinokurov, V.; Lvov, Y. M. Application of Halloysite Clay Nanotubes as a Pharmaceutical Excipient. Int. J. Pharm. 2017, 521 (1), 267– 273. (58) Fakhrullina, G. I.; Akhatova, F. S.; Lvov, Y. M.; Fakhrullin, R. F. Toxicity of Halloysite Clay Nanotubes in Vivo: A Caenorhabditis Elegans Study. Environ. Sci. Nano 2015, 2 (1), 54–59. (59) Wang, X.; Gong, J.; Rong, R.; Gui, Z.; Hu, T.; Xu, X. Halloysite Nanotubes-Induced Al Accumulation and Fibrotic Response in Lung of Mice after 30-Day Repeated Oral Administration. J. Agric. Food Chem. 2018, 66 (11), 2925–2933. (60) Cavallaro, G.; Donato, D. I.; Lazzara, G.; Milioto, S. A Comparative Thermogravimetric Study of Waterlogged Archaeological and Sound Woods. J. Therm. Anal. Calorim. 2011, 104 (2), 451–457. (61) Blanco, I.; Abate, L.; Bottino, F. A.; Bottino, P. Thermal Behaviour of a Series of Novel Aliphatic Bridged Polyhedral Oligomeric Silsesquioxanes (POSSs)/Polystyrene (PS) Nanocomposites: The Influence of the Bridge Length on the Resistance to Thermal Degradation. Polym. Degrad. Stab. 2014, 102 (0), 132–137. 32


Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(62) Gupta, B. S.; Jelle, B. P.; Gao, T. Wood Facade Materials Ageing Analysis by FTIR Spectroscopy. Constr. Mater. 2015, 168 (5), 219–231.

33



Page 34 of 34

TOC

34


Halloysite Nanotubes loaded with Calcium ... - ACS Publications

Recommend Documents