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Effect of Layered Hydroxide Salts, Produced by Two Different Methods, on the Mechanical and Thermal Properties of Poly(Methyl Methacrylate).

INTRODUCTION

Polymer/clay nanocomposites have been shown to provide enhancements in physical properties of polymers such as increased tensile strength, tensile modulus, flexural strength, thermal stability, and corrosion protection due to their structural morphology [1]. In addition to cationic exchanger clays from 2:1 groups like montmorillonite, synthetic anionic exchanger clays, such as layered double hydroxides (LDHs) and layered hydroxide salts (LHSs), have also been investigated for the same purpose. The structures of both families of synthetic compounds may be considered as based on the layered structure of brucite, (Mg[(OH).sub.2]) [2]. LHSs are formed when a fraction of the hydroxyl groups in the brucite-like structure is occupied by other oxoanions or water molecules or are directly grafted to the layers. In the first case, counterions are required in the second coordination sphere of the metal to stabilize the electrostatic charge. The general formula of a LHS is [M.sup.2+][(OH).sub.2-x][([A.sup.n.sub.-]).sub.x/n] x m[H.sub.2]O, where [M2.sup.+] is the metallic cation (e.g., [Mg.sup.+], [Ni.sup.2+], [Zn.sup.2+], [Ca.sup.2+], [Cd.sup.2+], [Co.sup.2+], and [Cu.sup.2+]) and A is a counterion with negative charge n- [3]. LHSs are synthesized by the same procedures to prepare LDHs. A number of easy and low-cost synthetic techniques have been successfully used in the preparation of LDHs. The most commonly used is a simple co-precipitation method; the second is based on the classical ion-exchange reactions [4].

Few studies have dealt with the synthesis and characterization of nanocomposites based on LHSs [1, 5-9]. As far as the authors know, there are only two papers [5, 6] in the literature about the synthesis and characterization of LHS/PMMA nanocomposites. Majoni et al. (2010) [5] prepared zinc hydroxide nitrate (ZHN) and then performed the anionic exchange with a boron-containing compound. PMMA nanocomposites were synthesized via melt blending, and three weight fractions of filler (3, 5, and 10 wt%) were evaluated. Thermogravimetric results demonstrated that composites were more thermally stable than PMMA and exhibited enhancements in [T.sub.10] (temperature at 10% mass loss) and [T.sub.50] (temperature at 50% mass loss) up until 44[degrees]C and 31[degrees]C, respectively. Kandare et al. (2006) [1] synthesized PMMA/copper hydroxy methacrylate (CHM) composites via solution blending (3 wt% of filler) and bulk polymerization (4 wt% of filler). Again, TGA results showed that the composite prepared via solution blending exhibited a significant enhancement on thermal stability. This nanocomposite showed [T.sub.l0], [T.sub.50], and [T.sub.90] (temperature at 90% mass loss) 33[degrees]C, 45[degrees]C, and 20[degrees]C, respectively, higher than PMMA. However, none of these studies evaluated the mechanical properties of PMMA/LHS nanocomposites. Besides, in these studies, melt blending or solution casting routes were used to prepare the nanocomposites.

The objective of this article is to prepare LHSs following two different methods and, after that, evaluate the mechanical and thermal properties of PMMA nanocomposites obtained by in situ bulk polymerization.

EXPERIMENTAL

Materials and Methods

Tert-butylperoxy 2-ethylhexyl carbonate (TBEC) (95%) (Sigma-Aldrich), sodium hydroxide (99%) (Exodo), calcium chloride (96%) (Ecibra), ethanol (99.5%) (Synth), copper(II) nitrate hemi(pentahydrate) (98%) (Sigma-Aldrich), zinc nitrate hexahydrate (98%) (Sigma-Aldrich), stearic acid (95%) (Sigma-Aldrich), azelaic acid (85%) (Sigma-Aldrich), myristic acid (99%) (Sigma-Aldrich), polyethylene glycol monolaurate (PEG monolaurate) ([M.sub.n] approximately 400 g/mol) (Sigma-Aldrich), silicone fluid (350 cps) (Dow Corning), and release compound (used in the injection procedure) (Dow coming) were of analytical grade and used as received.

Methyl methacrylate (MMA) (99%) (Sigma-Aldrich) was washed three times with a 10 w/v% sodium hydroxide solution and then three times with deionized water and dehydrated over calcium chloride.

Synthesis of Layered Hydroxide Salts

Zinc hydroxide nitrate (ZHN) [Zn.sub.5][(OH).sub.8][(N[O.sub.3]).sub.2]x 2[H.sub.2]O, and copper hydroxide nitrate (CHN), [Cu.sub.2][(OH).sub.3]N[O.sub.3], were prepared according to procedures described in the literature [10] and [1], respectively.

Sodium stearate and sodium myristate were prepared by reacting dispersions of stearic acid and myristic acid with a sodium hydroxide solution (10 w/v%). After reaching pH close to 8, the solution/dispersion was kept under stirring for 48 h. After this time, the mixture was centrifuged at 4000 rpm for 12 min, and the liquid supernatant was removed. The solids were dried in an oven for 7 days at 60[degrees]C.

During the synthesis of the disodium azelate, there was the formation of a soluble salt. This solution was stirred and heated at 90[degrees]C for 3 weeks, for the removal of water excess. After the precipitation of the salt, this solution/dispersion was centrifuged at 4000 rpm for 12 min, and the liquid supernatant was removed.

Although ZHN have nitrate available to be exchanged and in CHN, nitrate anions are grafted to the layers, we supposed that in the anionic exchange reactions of both LHSs, nitrate anions were replaced by the desired anions (stearate, myristate, azelate, or PEG[monolaurate]). In this procedure, ZHN or CHN were added to the organic anions solutions, under stirring, and the pH was adjusted to 8 using a sodium hydroxide solution (10 w/v%). The mixture was vigorously stirred for 3 days, after which the exchanged LHSs dispersions were centrifuged at 4000 rpm for 10 min and washed with deionized water. The centrifugation and washing processes were repeated for five times, and the solids were dried in an oven at 60[degrees]C for 7 days.

The LHSs were also synthesized by co-precipitation reaction (direct method). An intercalating agent solution/dispersion (0.0688 mol/L), in the case of ZHN, or (0.107 mol/L), in the case of CHN, was prepared. To this dispersion, a zinc nitrate hexahydrate solution was added (0.0172 mol/L), in the case of ZHN, or a copper (II) nitrate hemi(pentahydrate) solution (0.0214 mol/L), in the case of CHN. Finally, a sodium hydroxide solution (0.4 mol/L) was slowly and simultaneously added to keep pH close to 7. After the end of the reaction, the dispersion was stirred for 48 h. Later, the dispersion was centrifuged at 4000 rpm for 10 min and washed with deionized water. The centrifugation and washing processes were repeated for five times, and the solids were dried in an oven at 60[degrees]C for 7 days.

Preparation of PMMA Nanocomposites

Desired amounts of MMA (100 mL), TBEC initiator (0.04 mol/L), and LHSs (0.95541 g) were weighed, placed into a beaker, and mixed during 80 min at 70[degrees]C. Later, this beaker was charged in a home-made borosilicate glass reactor, whose temperature was maintained by mean of a Fisatom heating mantle model 67. The reaction was performed at 95[degrees]C for 75 min, under nitrogen atmosphere. The samples were ground using an IKA M20 grinder and passed through a 100 mesh sieve.

Characterizations

The X-ray diffraction (XRD) measurements were performed using a Shimadzu-XRD 7000 diffractometer, using Cu[K.sub.[alpha]] radiation ([lambda] = 1.5406 [Angstrom]), at a rate of 2[degrees]/min, operating at 40 kV and 30 mA, over 2[theta] range of 1.5-70[degrees].

Thermogravimetric analysis (TGA) was performed on a Shimadzu TGA-50M thermogravimetric analyzer, where the samples were heated from 30[degrees]C to 700[degrees]C, with a heating rate of 20[degrees]C/min on oxidant atmosphere (oxygen flow of 100 mL/min).

To carry out the mechanical tests, the samples were injection molded using a Haake Minijet injection molding system from Thermo Fisher Scientific. A release compound was used with the aim of facilitating the removal of the samples. The injection molding conditions adopted were: cylinder temperature of 280[degrees]C, injection pressure of 400 bar, injection time of 30 s, mold temperature of 60[degrees]C, holding pressure of 250 bar, and a holding time of 20 s. The specimens had 64 mm in length, 12.7 mm in width, and 3.2 mm in thickness. The cooling time was not considered during the injection procedure. After the end of each injection, the mold was withdrawn from the injection molding system. After the opening of the mold, all the samples were easily and quickly removed, still keeping their shapes. The measurements of the samples were confirmed before the mechanical tests were performed.

Dynamic mechanical analysis (DMA) were performed in a Netzsch, type DMA 242 equipment, using the holder for three-point free bending mode. The tests were done at a frequency of 1 Hz, 1 N force, and at oscillation amplitude of 15 micra. The analyses were carried out at a heating rate of 5[degrees]C/min and in the temperature range of 25[degrees]C to 200[degrees]C.

The flexural properties were measured using a MTS testing machine model 810, considering a three-point loading system. The testing speed was 5 mm/min, and span length was 50 mm.

RESULTS AND DISCUSSIONS

Layered Hydroxide Salts

The X-ray results for all species studied are shown in Figs. 1-4. The basal spacings of the fillers were calculated by Bragg's equation, using the position of the first order of the basal reflections.

CHN and ZHN exhibited basal spacings of 6.9 [Angstrom] and 9.65 [Angstrom], respectively. These values are in agreement with data previously reported in literature [10, 11], CHN(stearate) indirect and CHS (copper hydroxide stearate) direct revealed two series of basal reflections, with basal spacing of 34.5 [Angstrom] and 41.6 [Angstrom] (indirect) and 38.7 [Angstrom] and 46.5 [Angstrom] (direct) (Fig. 1). The existence of two crystalline phases may indicate that the organic anions are arranged in two different packing modes in the interlayer spacing. Basal spacing of 46.5 [Angstrom] is consistent with the formation of a bilayer packing [12]. The presence of two diffraction peaks at 12.8[degrees] and 25.78[degrees] (2 theta) (6.9 [Angstrom]), related to CHN, in the sample CHS direct indicated that CHN is the majority phase in the sample.

ZHN(stearate) indirect and ZHS (zinc hydroxide stearate) direct displayed basal spacings of 39.4 [Angstrom] and 42 [Angstrom], respectively. ZHN(stearate) indirect exhibited two diffraction peaks at 21.6[degrees] and 24.1[degrees] (2 theta), related to stearic acid (neutral), not totally removed after the washing process and present as a contaminant (Fig. 1).

CHN(myristate) indirect and CHM (copper hydroxide myristate) direct showed basal spacing of 36.8 [Angstrom] and 36.2 [Angstrom], respectively. Diffractions peaks at 12.76[degrees] (related to CHN) and 21.6[degrees] (related to myristic acid) were found in the XRD pattern of CHN(myristate) indirect. The presence of these diffractions peaks can indicate that nitrate anions were not completely replaced by the anions myristate and myristic acid is present in this sample, as a contaminant (Fig. 2).

ZHN(myristate) indirect revealed two series of basal reflections (fact that can be related with different hydration state of the LHS produced), with basal spacing of 30.9 [Angstrom] and 28.9 [Angstrom]. ZHM (zinc hydroxide myristate) direct exhibited a basal spacing of 30.2 [Angstrom] (Fig. 2).

Two series of basal reflections are showed in the XRD patterns for CHN(azelate) indirect (basal spacing of 14.6 [Angstrom] and 13 [Angstrom]) and ZHA (zinc hydroxide azelate) direct (basal spacing of 16.7 [Angstrom] and 11.9 [Angstrom]). CHA (copper hydroxide azelate) direct and ZHN(azelate) indirect displayed basal spacing of 14.8 [Angstrom] and 15.3 [Angstrom], respectively (Fig. 3). These basal spacings values are in agreement with those previously reported in literature for LDH(azelate) (11.8 [Angstrom], 13.5 [Angstrom], and 16.6 [Angstrom]) [3, 13]. The largest calculated distance that the ion azelate can occupy is 12.3 [Angstrom]. Considering the basal spacing of 16.7 [Angstrom], an interlayer spacing of 11.9 [Angstrom] is obtained which is consistent with the presence of azelate ions between the inorganic layers, oriented almost perpendicularly with respect to the layers' planes. Because azelate di-anion is formed by long carbon chain, different bending possibilities can fit in the interlayer space, thus leading to further orientation of the guest molecules [13].

CHP (copper hydroxide PEG monolaurate) direct and ZHP (zinc hydroxide PEG monolaurate) direct showed basal spacing of 11 [Angstrom] and 38.7 [Angstrom], respectively.

Figures 5 and 6 show thermogravimetric curves (TGA) for the oxidative thermal decomposition of the produced layered compounds ZHN and CHN, respectively.

For ZHN indirect, the samples containing stearate, myristate and azelate showed decomposition temperatures close to 517[degrees]C (char residue of 18.8%), 493[degrees]C (char residue of 39.4%), and 456[degrees]C (char residue of 46.4%), respectively.

For the zinc phases, obtained by the direct method, both the samples containing stearate and azelate exhibited thermal decomposition until 552[degrees]C, with char residue of 43.8% and 41.3%, respectively. ZHM suffered thermal decomposition until 553[degrees]C, with a char residue 61%; however, at 453[degrees]C, this sample had only 62% of its weight. ZHP suffered thermal decomposition until 593[degrees]C (char residue of 32.7%); however, at 476[degrees]C, this sample had only 33% of its weight.

For CHN indirect, the materials containing stearate and myristate showed decomposition temperatures of 511[degrees]C (char residue of 19.2%) and 288[degrees]C (char residue of 42%), respectively. CHN(azelate) indirect displayed thermal decomposition of 350[degrees]C (char residue of 49.7%). However, at 254[degrees]C, this sample had already lost 51.3% of its weight.

For the copper phases, obtained by the direct method, the samples with stearate, myristate, azelate, and PEG monolaurate revealed decomposition temperatures of 402[degrees]C (char residue of 37%), 463[degrees]C (char residue of 23.7%), 391[degrees]C (char residue of 35.4%), and 480[degrees]C (char residue of 20.9%), respectively.

These results can demonstrate that higher thermal stabilities can be observed when the layered compounds were synthesized by direct method, considering most of the LHSs evaluated in this study.

Polymer Composites

Figures 7 and 8 display the XRD patterns for PMMA/CHN and PMMA/ZHN composites, respectively. PMMA exhibits two characteristic broad diffraction peaks in the region of 15[degrees] and 30[degrees] (2 theta), attributed to semi-crystalline state of this polymer. These two contributions are observed in the case of the as-made composites, showing that, independently of the filler content, a similar crystallinity is reached [14]. Figure 7 shows that composites containing CHS and CHN(myristate) indirect exhibited diffraction bands at 12.82[degrees] (2 theta), related to CHN. No significant change in the basal spacing of the CHN was observed, indicating the formation of a composite with a partially immiscible phase.

The XRD of the cited LHSs demonstrated that no complete anion intercalation was performed and that there was a formation of polyphasic fillers. XRD patterns of the composites show that the broad diffraction peaks related to the LHSs phases, whose intercalation by the studied anions stearate (basal spacing of 46.5 [Angstrom] and 38.7 [Angstrom]) and myristate (basal spacing of 36.8 [Angstrom]) occurred, were not observed. This fact can be explained in two ways; either there was a delamination/exfoliation of the LHSs in the polymeric matrix, or their content is too small to be detected.

These facts can demonstrate that these systems should be described as mixed delaminated/exfoliated composites and phase separated composites (microcomposites). Composite containing CHA displayed a diffraction band at 5.66[degrees] (2 theta), which corresponds to a basal spacing of 15.6 [Angstrom], whereas this filler exhibited a basal spacing of 14.8 [Angstrom]. This small increase in the basal spacing can be attributed to the position of the sample in the sample holder, because minimum deviations can cause these changes in the basal spacing. Sample containing ZHA showed a diffraction band at 7.44[degrees] (2 theta) that can be related to filler phase with basal spacing of 11.9 [Angstrom]. The basal spacing did not change for this phase of ZHA in the composite which can reveal that a phase-separated composite was obtained. The characteristic XRD band at 5.3[degrees] (2 theta), with a basal spacing of 16.7 [Angstrom] attributed to ZHA phase, is absent. It is difficult to observe diffraction peaks related to the fillers at small concentration (1 wt%).

Figures 9 and 10 exhibit thermogravimetric curves and the derivatives of these curves (DTGA) for the oxidative thermal decomposition processes of PMMA and PMMA composites containing copper and zinc LHSs, respectively. Table 1 display a summary of thermogravimetric data.

TGA curves revealed that all the composites exhibited little faster degradation rates than PMMA, between 200[degrees]C and 250[degrees]C. This weight loss can be attributed to dehydration and dehydroxylation of the LHSs structures.

When 10% weight loss ([T.sub.10]) was selected as a point of comparison, the composites containing ZHA and ZHP exhibited the highest thermal stability. PMMA and both these composites displayed [T.sub.10] at 273[degrees]C and 320[degrees]C, respectively. At 50% weight loss ([T.sub.50]), the composite containing ZHN(stearate) indirect showed the major enhancement in thermal stability. [T.sub.50] increased from 314[degrees]C (PMMA) to 385[degrees]C (PMMA/ZHN(stearate) indirect).

When [T.sub.90] (temperature at which 90% weight loss occurs) was selected as a point of comparison, the composites containing ZHN(stearate) indirect and ZHN(myristate) indirect revealed the highest thermal stability. Compared to PMMA, both these composites displayed an enhancement of 71[degrees]C in [T.sub.90].

Composites with ZHA were much more thermally stable than the ones containing ZHN(azelate) indirect. For these composites, differences in [T.sub.10] and [T.sub.50] of 40[degrees]C and 32[degrees]C, respectively, have been found.

Considering the composites containing the copper LHSs, it was observed that the major enhancements in thermal stability were found for the composites containing CHN(myristate) indirect. This composite showed increases in [T.sub.10], [T.sub.50], and [T.sub.90] of 41[degrees]C, 63[degrees]C, and 52[degrees]C, respectively, compared to PMMA.

The mixing of the polymer with the additive may result in the increase of thermal capacity which, together with the barrier to heat transfer due to char formation, leads to degradation of the composites occurring at higher temperatures than the pristine PMMA [5].

Figures 11 and 12 show the storage modulus and tan delta as a function of temperature for PMMA and PMMA composites, containing copper and zinc LHSs, respectively. Composites based on CHM, ZHS, and ZHP displayed higher elastic modulus than PMMA throughout the studied temperature range. Composite PMMA/ZHP exhibited the highest values of elastic modulus until 78[degrees]C. This composite revealed at 60[degrees]C the same value of elastic modulus found for PMMA at 40[degrees]C (3,198 MPa). This result can demonstrate that composites containing only 1 wt% of certain layered compounds could be used at a temperature 20[degrees]C higher, keeping the same elastic modulus. Conceptually, polymer composites containing inorganic layered fillers are often expected to become stiff and more brittle [15]. The enhancement of this property depends on the distribution of the filler on the polymeric matrix. When the layered particles of the fillers are well-dispersed in the PMMA matrix, an improvement in physical and chemical interactions between these two compounds can occur, leading to an enhancement in the dynamic mechanical properties.

Figures 11 and 12 show that almost all the composites exhibited a higher glass transition temperature ([T.sub.g]) than PMMA. The only exception was found for the sample containing CHS that exhibited the same value of [T.sub.g] found for PMMA (108[degrees]C). This result can be related to physical interactions and chemical bonding between the LHSs and PMMA, which can restrict the mobility of the PMMA chains.

Figures 13 and 14 exhibit stress versus strain curves for PMMA and PMMA composites containing the copper and zinc LHSs, respectively. Table 2 displays a summary of the main parameters (modulus of elasticity, maximum flexural stress values, and elongation at break point) obtained from flexural test. The results revealed that higher elasticity modulus values were found for all the composites. Composites containing copper LHS obtained by the indirect method displayed higher elasticity modulus values than the ones obtained by the direct method. In contrast, higher values of this parameter were found for the composites of zinc obtained by the direct method. Compared to PMMA, the composite PMMA/ZHA exhibited an increase of 30% in this parameter.

Most of the composites revealed higher maximum flexural stress values than PMMA. The highest value of this parameter was found for the composite with ZHA, which displayed an increase of 17% in this property, compared to matrix. The enhancements of these properties are governed largely by the strong interfacial interactions between the filler layers and the polymer [16].

PMMA samples did not fracture during the tests. For other hand, all the nanocomposites exhibited a break point. The sample containing ZHN(azelate) indirect showed the lowest elongation at break value. This result is probably attributed to high resistance provided by the LHS layers against the deformation of PMMA [16].

CONCLUSIONS

An experimental study about intercalative in situ bulk polymerization of MMA in the presence of LHSs (CHN and ZHN) was carried out. All the studied fillers were synthesized following two different methods (direct co-precipitation (direct method) and by exchange reaction (indirect method). The filler percentage (wt %) in the PMMA was fixed at 1%.

Composites containing ZHA, ZHP, and CHM exhibited the most interesting results. Compared to PMMA, these samples revealed higher thermal stabilities, storage modulus, and maximum flexural stress values.

The results found in this investigation can indicate that the method of synthesis of the studied LHSs can influence in the mechanical and thermal properties of PMMA composites. The high potential application of these LHSs as anti-flame agents is under investigation.

ACKNOWLEDGMENTS

This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (CAPES)--Finance Code 001. We also thanks CNPq for the financial support (proc.: 303846/2014-3 and 400117/2016-9).

REFERENCES

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[3.] G.G.C. Arizaga, A.S. Mangrich, J.E.F.C. Gardolinski, and F. Wypych, J. Colloid Interface Sci., 320, 168 (2008).

[4.] G.G.C. Arizaga, C. Jimenez, A. Viruete, and J. Arratia-Quijada, "Functionalization of surfaces in layered double hydroxides and hydroxide salt nanoparticles," in Functionalized Nanomaterials, M. Farrukh, Ed., InTech, Croatia (2016).

[5.] S. Majoni, S. Su, and J. Hossenlopp, Polym. Degrad. Stab., 95, 1593 (2010).

[6.] E. Kandare, H. Deng, D. Wang, and J. Hossenlopp, Polym. Adv. 1 Technol., 17, 312 (2006).

[7.] W. Yang, L. Ma, L. Song, and Y. Hu, Mater. Chem. Phys., 141, 582 (2013).

[8.] R. Marangoni, L.P. Ramos, and F. Wypych, J. Colloid Interface Sci., 330, 303 (2009).

[9.] M. Silva, R. Marangoni, A.C.T. Cursino, W.H. Schreiner, and F. Wypych, Mater. Chem. Phys., 134, 392 (2012).

[10.] A.C.T. Cursino, J.E.F.C. Gardolinski, and F. Wypych, J. Colloid Interface Sci., 347, 49 (2010).

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[12.] B. Magagula, N. Nhlapo, and W. Focke, Polym. Degrad. Stab., 94, 947 (2009).

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Telma Nogueira (iD), (1) Fernando Wypych (iD), (2) Lucia Mei, (1) Liliane Lona (1)

(1) School of Chemical Engineering, University of Campinas, Campinas, Sao Paulo, Brazil

(2) Chemistry Department, Federal University of Parana, Curitiba, Parana, Brazil

Correspondence to: Telma Nogueira; e-mail; telma.nogueira@gmail.com

Contract grant sponsor: CNPq; contract grant numbers: 400117/2016-9; 303846/2014-3. contract grant sponsor: Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (CAPES) - Finance Code 001.

DOI 10.1002/pen.25081

Published online in Wiley Online Library (wileyonlinelibrary.com).

Caption: FIG. 1. X-ray diffraction patterns: (a) sodium stearate, (b) copper hydroxide nitrate (CHN), (c) copper hydroxide nitrate intercalated by the anion stearate, produced by indirect method (CHN[stearate] indirect), (d) copper hydroxide stearate, produced by direct method (CHS), (e) zinc hydroxide nitrate (ZHN), (f) zinc hydroxide nitrate intercalated by the anion stearate, produced by indirect method (ZHN[stearate] indirect), zinc hydroxide stearate, produced by direct method (ZHS).

Caption: FIG. 2. X-ray diffraction patterns: (a) sodium myristate, (b) copper hydroxide nitrate (CHN), (c) copper hydroxide nitrate intercalated by the anion myristate, produced by indirect method (CHN[myristate] indirect), (d) copper hydroxide myristate, produced by direct method (CHM), (e) zinc hydroxide nitrate (ZHN), (f) zinc hydroxide nitrate intercalated by the anion myristate, produced by indirect method (ZHN[myristate] indirect), zinc hydroxide myristate, produced by direct method (ZHM).

Caption: FIG. 3. X-ray diffraction patterns: (a) sodium azelate, (b) copper hydroxide nitrate (CHN), (c) copper hydroxide nitrate intercalated by the anion azelate, produced by indirect method (CHN[azelate] indirect), (d) copper hydroxide azelate, produced by direct method (CHA), (e) zinc hydroxide nitrate (ZHN), (f) zinc hydroxide nitrate intercalated by the anion azelate, produced by indirect method (ZHN[azelate] indirect), zinc hydroxide azelate, produced by direct method (ZHA).

Caption: FIG. 4. X-ray diffraction patterns: (a) polyethylene glycol monolaurate (PEG monolaurate), (b) copper hydroxide nitrate (CHN), (c) copper hydroxide PEG monolaurate, produced by direct method (CHP), (d) zinc hydroxide nitrate (ZHN), (e) zinc hydroxide PEG monolaurate, produced by direct method (ZHP).

Caption: FIG. 5. Thermogravimetric curves (TGA) for the oxidative thermal decomposition of the layered compounds containing ZHN.

Caption: FIG. 6. Thermogravimetric curves (TGA) for the oxidative thermal decomposition of the layered compounds containing CHN.

Caption: FIG. 7. X-ray diffraction of PMMA (a) and PMMA nanocomposites (b-h). (b) CHS, (c) CHN(stearate) indirect, (d) CHM, (e) CHN(myristate) indirect, (f) CHA, (g) CHN(azelate) indirect, (h) CHP.

Caption: FIG. 8. X-ray diffraction of PMMA (a) and PMMA nanocomposites (b-h). (b) ZHS, (c) ZHN(stearate) indirect, (d) ZHM, (e) ZHN(myristate) indirect, (f) ZHA, (g) ZHN(azelate) indirect, (h) ZHP.

Caption: FIG. 9. TGA and DTGA curves to PMMA and PMMA nanocomposites containing CHN.

Caption: FIG. 10. TGA and DTGA curves to PMMA and PMMA nanocomposites containing ZHN.

Caption: FIG. 11. Storage modulus and tan delta as a function of temperature for PMMA and PMMA nanocomposites containing CHN.

Caption: FIG. 12. Storage modulus and tan delta as a function of temperature for PMMA and PMMA nanocomposites containing ZHN.

Caption: FIG. 13. Stress versus strain curves derived from flexure tests to PMMA and PMMA nanocomposites containing CHN.

Caption: FIG. 14. Stress versus strain curves derived from flexure tests to PMMA and PMMA nanocomposites containing ZHN.
TABLE 1. Temperatures for the thermal
degradation of PMMA and PMMA composites.

Sample                          [T.sub.10]     [T.sub.50]
                               ([degrees]C)   ([degrees]C)

PMMA                               273            314
PMMA/CHS                           312            372
PMMA/CHN(stearate) indirect        312            365
PMMA/CHM                           312            372
PMMA/CHN(myristate) indirect       314            377
PMMA/CHA                           304            372
PMMA/CHN(azelate) indirect         305            370
PMMA/CHP                           310            373
PMMA/ZHS                           318            376
PMMA/ZHN(stearate) indirect        296            385
PMMA/ZHM                           312            374
PMMA/ZHN(myristate) indirect       296            378
PMMA/ZHA                           320            374
PMMA/ZHN(azelate) indirect         280            342
PMMA/ZHP                           320            374

Sample                          [T.sub.90]
                               ([degrees]C)

PMMA                               352
PMMA/CHS                           399
PMMA/CHN(stearate) indirect        408
PMMA/CHM                           400
PMMA/CHN(myristate) indirect       403
PMMA/CHA                           398
PMMA/CHN(azelate) indirect         394
PMMA/CHP                           402
PMMA/ZHS                           417
PMMA/ZHN(stearate) indirect        423
PMMA/ZHM                           417
PMMA/ZHN(myristate) indirect       423
PMMA/ZHA                           416
PMMA/ZHN(azelate) indirect         417
PMMA/ZHP                           416

TABLE 2. Summary of the some parameters obtained from flexure test.

                               Modulus of
                            elasticity (MPa)

PMMA                      2,674 [+ or -] 103.5
PMMA/CHS                  2,710 [+ or -] 54
PMMA/CHN                  2,902 [+ or -] 58.4
  (stearate) indirect
PMMA/CHM                  2,929 [+ or -] 176.8
PMMA/CHN                  2,963 [+ or -] 47.8
  (myristate) indirect
PMMA/CHA                  2,967 [+ or -] 386.5
PMMA/CHN                  3,016 [+ or -] 42.9
  (azelate) indirect
PMMA/CHP                  3,025 [+ or -] 116
PMMA/ZHS                  2,847 [+ or -] 113.7
PMMA/ZHN                  2,723 [+ or -] 35.4
  (stearate) indirect
PMMA/ZHM                  3,109 [+ or -] 58.7
PMMA/ZHN                  2,944 [+ or -] 88.3
  (myristate) indirect
PMMA/ZHA                  3,467 [+ or -] 331
PMMA/ZHN                  2,955 [+ or -] 86.6
  (azelate) indirect
PMMA/ZHP                  3,004 [+ or -] 78.6

                            Maximum flexural        Elongation
                          stress values (MPa)      at break (%)

PMMA                       104 [+ or -] 1.9            --
PMMA/CHS                   102 [+ or -] 2.3      6.5 [+ or -] 1.6
PMMA/CHN                    98 [+ or -] 2.8      4.4 [+ or -] 0.06
  (stearate) indirect
PMMA/CHM                   109 [+ or -] 5.1      7.45 [+ or -] 2.2
PMMA/CHN                   111 [+ or -] 6.9      5.4 [+ or -] 0.62
  (myristate) indirect
PMMA/CHA                   110 [+ or -] 5.9      5.1 [+ or -] 1
PMMA/CHN                   114 [+ or -] 6.9      5.5 [+ or -] 0.66
  (azelate) indirect
PMMA/CHP                   114 [+ or -] 4          6 [+ or -] 0.4
PMMA/ZHS                   101 [+ or -] 30.2       5 [+ or -] 1.7
PMMA/ZHN                    99 [+ or -] 6.6      5.2 [+ or -] 0.8
  (stearate) indirect
PMMA/ZHM                   110 [+ or -] 10.9     4.6 [+ or -] 0.9
PMMA/ZHN                   105 [+ or -] 0.96     4.9 [+ or -] 0.4
  (myristate) indirect
PMMA/ZHA                   122 [+ or -] 8.8      4.5 [+ or -] 0.8
PMMA/ZHN                    94 [+ or -] 5.4      3.6 [+ or -] 0.35
  (azelate) indirect
PMMA/ZHP                   113 [+ or -] 12.5       5 [+ or -] 0.75
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Author:Nogueira, Telma; Wypych, Fernando; Mei, Lucia; Lona, Liliane
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:3BRAZ
Date:May 1, 2019
Words:4995
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