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GEOPOLYMER AS MATRIX APPLIED IN COMPOSITES WITH

NATURAL FIBERS

E. A. S. Correia1

, M. E. O. Alexandre2

 1Universidade Federal da Paraíba - UFPB, João Pessoa/PB –  Brazil

2Instituto Federal de Educação, Ciência e Tecnologia da Paraíba-IFPE, João Pessoa, Brasil

 ABSTRACT

The development of new technologies has boosted searches for obtaining competitive and

ecologically viable materials cost benefit attractive to the market. The main goal of this work

was to develop and study geopolimérica matrix composites reinforced with fibres of vegetable,

 for application as alternative non-conventional material in several areas. Noted the technical

 feasibility of such materials through the results achieved when subjected to mechanical and

 physic-chemical associated with the modern techniques of microestruturais characterizations.

The bursting and compression module, array and composite material, was compatible with the

minimum established resistance and validated in the market when compared to the similar hues

screeds. When subjected to pressure, low energy composites showed outstanding degree of

 packaging, lower porosity, resistivity and better ductility and excellent stage of deformation.

 Keywords: Geopolymer 1 , Natural Fibers2 , Composites 3.

1. INTRODUCTION

Advances in the development of composite materials have brought significant results as toits applicability (MATTOSO,1996). However it is notable that some reinforcements traditionalexpose their limitations and compromises its mechanical performance. This is because with time,these materials lose their tenacity and endurance due to the alkalinity of the array. The relentlessquest for the most versatile building materials, with greater economic potential and low cost,have targeted searches to work with natural fibres (AZIZ, 1987), which in addition to improvingthe mechanical performance of the array, has good resistance to chemical instability establishinga greater resistance to the matrix, however still exists the need to find satisfactory conditions foroptimizing the interface, as well as enhance operationalization in productive scale.

The technique of applying natural fibres such as strengthening agent in arrays slabs have been used since the mid-1940s when James Hardie and Copy Pty Ltd has replaced asbestos by pulp cellulose as strengthening agent in cement-based laminates. In Brazil, this technique beganto be developed by the research and Development Center in Bahia, applying natural fibers inconcrete matrix (SIVARAJA, 2009). This new line of research brings to light a new variable forcomposite materials, opening up new fields of application, in addition to using renewableresources, which contribute to the reduction of contamination of the environment.

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  Compound as aluminosilicates form a matrix resistant high temperature (BARBOSA,2003;COLEMAN,2005), have high power to accession and satisfactory ability to cure at roomtemperature, the Geopolymer (DAVIDOVITS,2002; DUXTON,2006) like most arrays screeds,has a low mechanical strength, which limits its scope. To obtain a significant gain in strength,especially when subjected to mechanical tests, inserting vegetable fiber composite qualities

raises and extends its scope.2. MATERIALS AND METHODS

2.1. Materials

As a source of silicon and aluminum matrix used the supplied by Caulisa SA kaolin, kaolin processing industry located in the municipality of Juazeirinho, PB; the vegetable fibres were provided by COSIBRA  –   Company Sisal of Brazil. Sodium silicate was provided byPernambuco Chemistry S/A with a silica (SiO2/Na2O ratio, by mass) roughly 2.5 and pH around13.

2.2. Synthesis process

The process of synthesis occurred in two steps. In the first stage was calcinedkaolin(DUXTON2006), in a muffle furnace at 750 ° C for 2 h, so that the entire exercised bykaolinite in metacaulinita(PALOMO,2003; VAN JAARSVELD,2002), then use the sodiumsilicate in appropriate proportion with Activator alkaline, the bubbles have been eliminatedthrough intermittent vibration. In the second step the fibers with approximately 60 mm in lengthwere arranged in two layers of 3 mm and interspersed by matrix in the ratio of 3%, until fillingmold, this process was repeated until all layers were released by filling in a uniform mannerthroughout the mold cavity.

Again, the bubbles have been eliminated by placing the template fully populated on ashaking platform. After the molding process, shapes underwent a process of cure in an oven at 55° C for 48 hours. After this period, the mold rested for over 48 hours under ambient temperature,so that ultimately were subjected to the tests of characterization.

(a)  (b)Figure 1: Three-point bending test during and after the break

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 (a)  (b)

Figure 2: Tests simple and diametric compression

2.3. Characterization of materials

The characterization of materials, precursors and of the bodies evidence instrumentaltechniques was carried out as described below:-the determination of the moisture content of thefibres(LADCHUMANANANDASIVAM,2005;  GHAVAMI,1999) of the Agave Sisalana wasconducted according to standard (American Society for Testing and Materials) ASTM 1413-76;the analyses via wet (titration) were held in order to determine the concentration of acidic groupsof samples; The content of water-soluble extractives was determined by standard TAPPI T212om-98. -Images of the surfaces of vegetable fibres were obtained from secondary electrons andSpread in a scanning electron microscope JSM 5800 LV a JEOL brand.

The accelerating voltage of the electron beam generated from a tungsten filament was equalto 10 kV.

Compression test, conducted in the laboratory of Rural Constructions  –   Seals/UFCG, was

used the Universal type compression machine. Test compression was accomplished using thecylindrical body of evidence with the following dimensions: 5 cm in diameter and 10 cm inheight, as in Figure 2. The test of resistance to traction in bending Universal Machine was usedfor the testing of 03 points, as shown in Figure 1, with the following schedule: 03 batches with 5 bodies of evidence each with dimensions 4cmx4cmx16cm, at the age of 30 days, both tests withspeed 2 mm s-1.Chemical analysis was held at the Rapid laboratory Scale of UFPB in Sequentialx-ray Fluorescence Spectrometer XRF-1800 model of Shimadzu.

3. RESULTS AND DISCUSSION

3.1. Geopolymer Formulations of folder

The chemical composition(PALOMO,2003) of metacaulinita activatedalkaline(FERNÁNDEZ-JIMÉNEZ,2005; GLUKHOVSKY, 1980; and GOMES,2007) withsodium silicate PQ-1.65, was analyzed by x-ray Florescence (XRF) in laboratory scale rapidUFPB.

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Table1: Chemical compositions of the Geopolymer folder.

constituents SiO2  Na2O Al2O K2O Cl Fe2O3  CaO TiO2  SO3  P2O5  NiO

% 72.7895 12.9737 12.8665 0.4329 0.3769 0.3008 0.1291 0.0537 0.0409 0.0295 0.0064

3.2. Physico-chemical properties of fibres

As the Lignocellulosic are highly hygroscopic materials is very important to thedetermination of the moisture content of The soluble in cold water include organic salts, sugars,resins and tannins.

Table 2: Physico-chemical properties of vegetable fibres

Parameters Agave Sisalana Ananás ComososMoisture content (%) 10,48 10,11

Acidic groups (mol/l) 0, 00186 0,00146Water-soluble extractives (%) 6,84 7,19

 pH 7,69 6,96Density (g/m3) 1,32-1,45 1,30-1,44

Lignin (%) 6-11 5-12Cellulose(%) 65-73 70-83

Hemicellulose(%) 13,33 18Diameter (μm)  50-300 50-105

Hygroscopicity (%) 10-13 9-11L/D 103 460

Angle expiral(°) 20 15Length (cm) 30-140 20-120

Uma das limitações das fibras vegetais no obtenção de compósitos é a elevadahigroscopicidade e o alto teor de extrativos solúveis presentes na superfície,o que dificulta ainteração física da matriz com o agente de reforço, a baixa densidade da fibra de ananás emrelação a fibra de agave, proporciona elevada razão de aspecto (L/D), favorável a ancoragem dafibra de ananás na matriz geopolimérica, outro aspecto positivo é o elevado teor de lignina nestafibra, que age como agente plastificante, otimizando a estabilidade da interface.

3.3. Mechanical strength properties

3.3.1. Three point bending tests

Been tested 45 bodies of evidence, 15 in 3 batches of five and 30 in 6 batches of fivefollowing batches for array, matrix, with agave sisalana and matrix with pineapple comosos at aratio of 3% by volume for randomly distributed reinforcing agent with approximately 25 mm inlength. Bending tests were conducted at three points on a machine SHIMADZU AG-X , withload cell of 50 kN, where the body of evidence was positioned with the load applied at the center

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of even with going to encyclopedia of 120 mm and with a speed of 2 mm/min, defined by NBR13279 (2005) and temperature about 25 °C. Figure 1 (a) shows the outline of the test. The resultsobtained are represented in the form of graph (Stress x Strain), figures 3 and 4.

Figure 3: Array behavior in three-point bending tests.

(a) Strain (% ) (b) Strain (%)

Figure 4: Behavior of composites with agave sisalana (a) and with pineapple comosos (b) for the three points bending tests.

Média

Média

Média

Stress(MPa)

Tensão(MPa)

Stress(MPa)

Strain (%)

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  Compression tests were conducted on a machine SHIMADZU AG-X 100, with load cell of100 kN, where the bodies of evidence were positioned as Figure 2 (a) (b) and with a speed of 2mm/min, defined by NBR 7215 (1991), and temperature about 25 ° c. The results obtained arerepresented in chart form (Stress x Strain), figures 5, 6,7 and 8.

3.3.2. Axial compressão tests

Strain(%)

Figure 5: Average curve for simple compression test with the array.

(a) Strain(%) (b)Strain(%)

Figure 6: Average curves for simple compression tests with composites of agave sisalana pineapple (a) andananás comosos (b)

Média

Média Média

Stress(MPa)

Stress(MPa)

Stress(MPa)

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3.3.3 Diametral compression test

Strain(%)

Figure 7: Average curve to diametral compression test with the array.

(a) Strain (%) (b) Strain (%)Figure 8: Average curves for compression tests with diametral composites agave sisalana pineapple (a) and

ananás comosos (b) 

Média Média

Média

Stress(MPa)

TStress(MPa)

TStress(MPa)

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  Analisando o comportamento da Figura 3, verifica-se que o valor médio obtido para tensãode flexão foi 1,4Mpa para matriz, valor razoável para os padrões encontrados na literatura paramateriais cerâmicos, na figura 4, podemos perceber valores entre 2 e 3 Mpa para matrizesreforçadas com fibras vegetais, os valores alcançados para módulos de ruptura também sãoexpressivos e ocorrem com uma taxa de deformação superior aos da matriz sem agente de

reforço.3.4. Micro-structural studies

Figure 5: Microstructure of the surface of the Figure 6: Microscopy in composite withfibres of sisal in natura. leaf of sisal fiber in Geopolymer.

Figure 7: Microstructure of the surface of the Figure 8: Microscopy in composite withfibres of ananás in natura. leaf of ananás fiber in Geopolymer

As alterações morfológicas observadas nas fibras vegetais inseridas na matriz foramobservadas através de MEV, nesse trabalho utilizamos fibra in natura pois a matriz já possuielevada alcalinidade (pH=13), logo evitamos a fragilização do agente de reforço por tratamentoquímico excessivo; na figura 6, observamos espaços vazios na interface fibra-matriz, todaviaestes espaços estão minimizados na figura 8, onde foi utilizados fibra de ananás como reforço,isto ocorre em função do baixo teor de extrativos solúveis presentes nessa fibra do abacaxizeiroque é menor em torno de 11% aproximadamente.

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 3.5. Termogravimétricas Analyses

0 100 200 300 400 500 600 700 800 900

0

2

4

6

8

10

12

14

 DTG-FLS

 DTG-FLSM

 TGA - FLS

 TGA - FLSM

Weight(%mg)

Temperature (°C)

-0,2

-0,1

0,0

0,1

0,2

0,3

Deriv.Weight(%mg/min)

 

Figure 9:  TG and DTG curves for fibers of agave sisalana in natura and mercerizadas

0 100 200 300 400 500 600 700 800 900

-20

-10

0

10

20

30

40

50

60

Weight(%

mg)

Temperature (°C)

 FLS

 FLSM

 

Figure 10: DTA curves for agave sisalana in natura and mercerizadas

A figura 9, mostra ascurvas de TG/DTG parafibras de sisal in natura etratadas com NaOH(2%)

durante 48h e expostas aoar por 15dias, podemos perceber dois estágios dedecomposição de 10-12%de água, 50-65% de polissacarídeos eaproximadamente 30% deresíduos. Observamosatravés dos resultados que aamostra sem tratamentoapresentou maior taxa de

decomposição no entornode 300-400°C.

Constatamos através dacurva DTA (figura 10) parafibra de sisal, um eventoendotérmico entre 65-75°C e

outro no intervalo de 400-420°C, dois picosexotérmicos na temperaturamáxima de 360°C e 460°C,na região de transição, adegradação térmicaacentuada ocorreu entre 300-400°C e coincide com aanálise TG/DTG.

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0 100 200 300 400 500 600 700 800 900

2

4

6

8

10

12

14 TGA - FLA

 TGA - FLAM

Weight(%)

Temperature (°C)

Deriv.Weight(%/min)

 DTG - FLA

 DTG - FLAM

-0,20

-0,15

-0,10

-0,05

0,00

0,05

0,10

 

Figure 11:  TG and DTG curves for fibers of ananás comosos in natura and mercerizadas.

0 300 600 900

-40

-20

0

20

Temperature (°C)

Temperaturedifferenc

e(°C/mg)

 DTA - FLA

 DTA - FLAM

 

Figure 12: DTA curves for ananás comosos in natura and mercerizadas

A figura 11 mostra ascurvas de TG/DTG para fibra deananás comosos, nas mesmascondições relatadasanteriormente, onde podemosobservar dois estágios dedecomposição, o primeiro a

60°C, referente à perda de águae o segundo a365°C, referente adecomposição principal. Foinotado um resíduo de 1, 5 a 2,5% a 800°C. A curva DTGapresentou dois estágios dedecomposição, o primeiro a60°C, correspondente ao calorde vaporização e o segundo a355°C, onde a decomposição foimáxima

A análise de curva DTA,apresentou pequenos eventostérmicos positivos e escassos pontos caloríficos significativosconforme a figura 12, a fibra in

natura apresentou resultadosexotérmicos discretos enegativos, todavia para fibrasmercerizadas observamos um pico máximo em torno de 415°C.

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4. CONCLUSIONS

A presença de fibras vegetais na matriz confere tendência de crescimento na resistência àflexão, até um teor ótimo, com posterior redução desta propriedade, a capacidade de absorverenergia (tenacidade) foi a propriedade mais sensível influenciada pelo acréscimo das fibras. Os

compósitos com fibras de ananás comosos apresentaram valores elevados para energia específica(tenacidade) e resistência à flexão em relação aos corpos de prova com fibras de agave sisalana, para todos os esforços utilizados. Isto se deve, provavelmente, ao maior número de fibras porunidade volumétrica da matriz, pois as fibras de ananás comosos apresentam maior relação deaspecto (L/D) devido ao menor diâmetro, e a maior concentração de fibras na região de interface,o maior teor de lignina destas fibras também proporciona maior rigidez e elasticidade.

A curvas termoanaliticas mostraram que as fibras apresentam estabilidade em torno de300ºC, podendo ser aplicadas em materiais refratários, isolantes térmicos e acústicos. As fibrasda folha do abacaxizeiro têm grande potencial na aplicação na engenharia mecânica em materiaiscompósitos para a fabricação de carcaça de automóveis, pára-choques, painéis de carros, em barcos, caixas de água, cabine telefônica, caixas de correio, depósito de lixo, etc., ainda

despertam particular interesse da construção civil para compósitos de matriz geopoliméricadesenvolvidos para design de interiores ecologicamente corretos.

5. ACKNOWLEDGMENTS

We acknowledge all the partners and friends who collaborated to the development that job, providing us every necessary material to confection our specimens between them, the COSIBRAS.A., Caulisa S.A. and Chemistry S.A. Acknowledge too, all the laboratories who collaborated toanalyzes and characterizations our specimens made in the LABEME and LSR in the FederalUniversity of Paraíba. The characterization was made in the LACOM on UFPB, and a

mechanical test was executed in mechanical laboratory of the IFPB and Rural Constructionslaboratory –  LaCRA/UFCG..

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