PHENOLIC RESINS AND COMPOSITES PHENOLIC COMPOSITES ...€¦ · pure fuel and as a gasoline enhancer [16,17]. The process in general consists of the hydrolysis of a lignocellulosic

Nicolais weoc167.tex V2 - 02/20/2012 4:48 P.M. P. 2059

PPHENOLIC RESINS AND COMPOSITES

ELISABETE FROLLINI

University of Sao Paulo, SaoCarlos, Brazil

ALAIN CASTELLAN

Universite de Bordeaux,Pessac, France

INTRODUCTION

Since the work by Baekeland [1] to prepare highlycross-linked plastics by transforming monomeric oroligomeric phenols into attractive polymeric materials,phenolic resins have constituted a large commodity resinsystem. Phenolic resins mainly belong to the class ofthermosetting resins, such as epoxies, bismaleimides,polyimines, cyanate esters, and polybenzoxazines [2].

From early times, phenolic resin combined with awood flour filler, because of its heat resistance and elec-trical nonconductivity, has been used in radios, tele-phones, and electrical insulators. The molding of prepregs(preimpregnated fibers and fabrics) rendered the firstfiber-reinforced composites, which, mainly because of theircost, were used initially (1930s) in aircraft and spaceapplications, followed by some automotive applications.They found a niche for great expansion in the electronicsindustry [3].

Despite their brittleness, the prominent advantageousfeatures of phenolic resins are their ubiquitous bindingproperties for a variety of substrates ranging from wood,glass, metals, cellulosic and lignocellulosic fibers, and oth-ers. Their excellent thermal behavior; their high strengthlevel; their long-term thermal and mechanical stability;their excellent fire, smoke, and low toxicity character-istics; their very good electrical and thermal insulatingcapabilities; and their favorable cost/performance char-acteristics surpass those of most other polymeric resinsystems [4].

One of the major contributions of phenolic resins is theiruse as a matrix in fiber-reinforced composites to preparematerials with low fire-smoke toxicity coupled with favor-able economics and excellent properties. These featuresmake them suitable for applications in transportation,namely in aircraft, aerospace, and auto industries, in addi-tion to other applications such as the electric and electronicindustries [2]. New formulations became available in the1980s and were developed mainly to meet the require-ments of the mass-transit fire code, which allowed theapplication of phenolic composites in new areas, such asin mass-transit car interiors and architectural and marinecomponents [3]. These facts, added to their properties, ledto a favorable conjunction for phenolic composites, makingthem widely used when the requirements of both publicand worker safety are of primary importance.

PHENOLIC COMPOSITES

Phenolic Matrices from Phenolic Resins/Formaldehyde

There are basically three types of phenolic resins: thetraditional resoles and novolacs and the more recent poly-benzoxazines [5]. The reaction of formaldehyde (F) inexcess with phenol (P) under alkaline catalysis forms aheat reactive pre-polymer, which can be cross-linked byheat and an accelerator such as resorcinol (10% basedon phenol) to form a resole thermoset (Fig. 1). When thephenol is in excess and under acid catalysis, a novolacpre-polymer is formed. The latter can be cross-linked byheat and a catalyst such as hexamethylene tetramine(Fig. 1). The benzoxazine monomers were prepared fromphenol, formaldehyde, and amine (aliphatic or aromatic).Their curing does not require a strong acid catalyst, andthere is no release of by-products. The resins possess anear-zero volumetric change on curing and display lowwater absorption (Fig. 2).

Phenolic Matrices from Lignophenolic Resins/Formaldehyde

Lignin, a phenolic biopolymer present in wood andnon-wood plants, is a by-product of the pulp and paperindustry. Lignin is mainly burned as fuel to recover thebase, as in the Kraft process [6]. A small amount oflignin sulfonates, which are by-products of the sulfitepulping process, is used as dispersants, oilfield drillingmuds, concrete additives, and adhesive extenders.Environmental concerns led to the increased use ofmaterials obtained from biomass as raw materials forthe production of biofuels, bioenergy, biomolecules, andbio-based products [7–9]. Delignification of lignocellulosicmaterials (wood and non-wood plants) in nonaqueousmedia (organosolv process), mainly in acidic media, leadsto low molecular-weight lignophenolic polymers, whichare used as a partial replacement of phenolic resin inplywood, oriented strand board (OSB), and waferboard[4]. Although the organosolv lignins have been extensivelystudied [10–13], their chemical potential has not stillbeen well explored. Saccharification and fermentation ofnon-wood plants appears to be a very promising processto produce bioethanol [14,15], which is used both as apure fuel and as a gasoline enhancer [16,17]. The processin general consists of the hydrolysis of a lignocellulosicmaterial of the organosolv type [17–20] using ethanoland diluted sulfuric acid [21–23]. It compares well withother known processes, such as the Alcell process [24],and other acidic pretreatments developed recently in thebiorefinery processes [25]. For economical availability,the industrial applications of lignin should be developedthrough higher added value products, where problemsrelated to heterogeneity and color are not decisive [9,26].The presence of biorefineries in many countries, aimingto convert lignocellulosic wastes into fuels and chemicalraw materials, has led to the availability of large-scale

2059


2060 PHENOLIC RESINS AND COMPOSITES

F/P < 1

OH OH

HeatNovolac thermoset

Novolac pre-polymer

H+

HO OH

o–p′ > p–p′ > o–o′

HMTA

NN

N

N

10%

OH

+ CH2O

F/P > 1

OH OH

CH2OH

CH2OH

OH

CH2OH

Heat

OH

OH

10%

Resole thermoset

Base

P

F

Resolepre-polymer resorcinol

Figure 1. Schematic of the formation of resole and novolac resins according to Gardziella et al. [4].

+ RNH22 CH2O NHO OH

ROH

N

O

R

Δ

R′

R′

Polybenzoxazines

OH

N

Rn

R′Benzoxazines

Figure 2. Schematic of the formation of polybenzoxazines according to Gardziella et al. [4] and Ghosh et al. [5].

lignin, which gives it strategic importance as a substituteof phenol in phenolic resins [27].

The lignin structures contain aliphatic and aromaticgroups with several substituted phenylpropane ringslinked by different types of bonds, such as carbon–carbonor ether [28,29]. The main units, guaiacyl (G), syringyl (S),and p-hydroxyphenyl (H), differ in terms of the presence ofortho methoxyl groups in the aromatic rings [30] (Fig. 3).These phenolic aromatic rings can replace phenol toprepare phenolic resins presenting both environmentallyand economically interesting alternatives to PF resins[31]. The synthesis of lignin–formaldehyde resins consists

primarily in a hydroxymethylation step. Lignin extractedfrom non-wood plants has a greater number of activecenters toward formaldehyde in comparison to ligninextracted from wood due to the higher proportion ofp-hydroxyphenyl units in aromatic rings [32]. In theserings, electrophilic attacks can easily occur on free orthopositions (related to the hydroxyl group) [30,33,34], whichincreases the reactivity (Fig. 3). Moreover, the ligninextracted by organosolv processes has superior thermalproperties when compared to lignin obtained throughKraft or sulfite processes [35]. Lignophenolic matrices(lignin–PF) reinforced with fibers from sugarcane bagasse

CHOH

HC

CH2OH

O

R2

OH

R1

R1

R2

Lig

Lignin

R1 = R2 = H; p-Hydroxyphenyl unit

R1 = OCH3; R2 = H; Guaiacyl unit

R1 = OCH3; R2 = OCH3; Syringyl unit

CH2O

CHOH

HC

CH2OH

O

R4

OH

R3

R1

R2

Lig

R3 = R4 = CH2OH

R3 = OCH3; R4 = CH2OH

R3 = OCH3; R4 = OCH3

R1 = R2 = H

R1 = OCH3; R2 = H

R1 = OCH3; R2 = OCH3

Hydroxymethylated Lignin

R3 = R4 = CH2OH

CHOH

CH

CH2OH

OH

OR1

R2

Lig

CH2

CHOH

CH

CH2OH

OH

OR1

R2

Lig

CH2

n

CHOH

CH

CH2OH

OH

OR1

R2

Lig

CH2

Lignin-formaldehyde pre-polymer

NaOH

Figure 3. Main units in non-wood plant lignin and schematic representation of lignin–formaldehyde pre-polymers according to Ramires et al. [30] and Malutan et al. [32].


PHENOLIC RESINS AND COMPOSITES 2061

(a) (b)

CH

OH

CH

HO

O

O

OH

n

HC

OH

O

n

CH

O

OH

Figure 4. Structure of major (a) and minor (b)phenol–furfural oligomers supported by MALDI-TOF massspectrometry according to Oliveira et al. [41].

(biorefinery by-product) have already been described toprepare fiberboards [32]. Currently, researches devoted tomaking composites reinforced with lignocellulosic fibersobtained from renewable sources are in constant devel-opment [36]. These fibers can advantageously replacesynthetic fibers, such as glass, aramid, and carbon. Thestructure and the nature of the fiber–matrix interfaceplay an important role in the mechanical propertiesof composite materials because the load transfer fromthe matrix to the fiber occurs through the interface.The presence of aromatic moieties in both the fiber andmatrix can increase their mutual affinity and improve theadhesion at the fiber–matrix interface.

Phenolic and Lignophenolic Resins with Other Aldehydes

To decrease the dependence of PF resins on formalde-hyde, and hence their formaldehyde emissions, phenolic–furfural (PFu) resins have been developed [37]. Furfuralis a slower reacting aldehyde than formaldehyde, but itis obtained from natural sources by acid hydrolysis ofabundant agricultural and forestry waste residues [38].PFu resins have mainly been used as exterior-grade struc-tural wood adhesives [39] and also for cold-setting bindersfor foundry core sand [40]. PFu pre-polymers have beenused as thermoset matrices reinforced by natural fibers tomake composites [41]. The structures of the resins havebeen studied by NMR spectrometry and matrix-assisted

laser desorption/ionization time-of-flight (MALDI-TOF)mass spectrometry experiments with the help of synthe-sized molecular model compounds. A majority of linearoligomers (Fig. 4a) and a minority of cyclic oligomers(Fig. 4b) constitute the main parts of the resins [41].Composites displaying excellent properties and using ahigh proportion of materials obtained from biomass with-out formaldehyde were prepared using furfural–phenolresins and sisal fibers [41].

Low vapor tension and low toxicity of glyoxal(OHC–CHO) solutions constitute some of the advan-tages of using glyoxal instead of formaldehyde formany applications [42]. Glyoxal has already replacedformaldehyde in wood adhesive applications [43–45].Glyoxal is a dialdehyde that can be obtained from severalnatural sources, such as from the oxidation of lipidsor as a by-product of biological processes [46]. The twoadjacent carbonyl groups make glyoxal highly reactive. Inaddition, glyoxal has been used [36] to prepare phenolicpre-polymers in alkaline conditions to make compositescomposed of glyoxal–phenol thermoset resins reinforcedby sisal fibers (30%, w/w), because of their excellentmechanical properties. Some molecular structures of theresins have been proposed on the basis of NMR analyses(Fig. 5a). Although the curing temperature was limited to150◦C, the composites displayed good adhesion betweenthe resin and the sisal fibers in addition to excellentdynamical-mechanical properties [36].

HO

O

O

OHO

HO

HO HO

H

(a) (b)

OHO

OH

OH

OH

OHO

OH

OH

OH

OH

Figure 5. (a) Structure of phenol–glyoxal oligomers according to Ramires et al. [36]. (b) Representation of condensed tannins [49].



Glyoxal was also used as a substitute for formaldehydein the synthesis of a novolac-type phenolic resin usingoxalic acid as a catalyst, which can also be obtained fromrenewable sources, to prepare composites reinforced withmicrocrystalline cellulose (MCC) (30–70% w/w) [48]. Scan-ning electron microscopy (SEM) images of the fracturedsurfaces showed that the composites presented a goodreinforcement/matrix interface, and dynamic mechanicalthermo-analysis revealed that the composites had highstorage modulus at room temperature. Moreover, the com-posites reinforced with 30% MCC displayed almost thesame water absorption as the phenolic thermoset usedin industrial applications [47]. Glutaraldehyde, anotherdialdehyde, has also been used with success to preparelignophenolic resole type resin [48].

Phenolic and Phenolic Tannin Resins

The macromolecules of condensed tannins (polyflavonoids)(Fig. 5b) can vary in size, for instance, from 2 to 10 or 12condensed monomer units. The phenolic groups presentin tannins enable this macromolecule to participate inthe same reactions as phenol [49]. The condensed tan-nins are suitable to prepare a phenolic-type polymericmatrix because of the presence of phenolic rings witha larger number of free positions (Fig. 5b), where theelectrophilic attack can occur [50]. The high reactivity ofmost polyflavonoids toward the aldehydes, similar to thatof resorcinol, is due to the presence of hydroxyl groupslinked to the rings in meta positions and represents anadvantage of condensed tannins over phenol. Therefore,condensed tannins show a great potential for their use withformaldehyde [51]. Condensed tannins can be obtainedfrom the bark of the mimosa and/or acacia trees [50,52].Barbosa et al. [50] reported the preparation of bio-basedcomposites including tannin/phenol/formaldehyde resinsreinforced by coir fibers, whereas Lei et al. [52] describedtannin/lignin/glyoxal resins as adhesives for wood partic-ulate boards.

INTERFACES

The adhesion at the matrix–reinforcement interface isa very important property of composites. Strong adhe-sion leads to good mechanical properties because the loadis transferred from the matrix to the fiber through theinterface. Ballistic fiberglass–phenolic composites can behighlighted as an exception because the failure at theinterface allows a better dissipation of energy, treatingthe glass plies as discrete entities [53]. In general, at themolecular level, phenolics have good interactions mainlywith surfaces on which groups can establish hydrogenbonds with the phenolic hydroxyl groups. In addition, thepresence of aromatic rings in the chemical structure ofthe reinforcement also can improve the adhesion. Thesefeatures (the possibility of establishing hydrogen bondsor other structural characteristics, such as the presenceof aromatic rings) are not always present in the rein-forcement, which leads to the necessity for modifications,normally of the fiber surface. The type of modification that

is appropriate is mainly defined by the structural char-acteristics of the reinforcement of the phenolic matrix. Inthis way, the adhesion can be improved, making it possi-ble to harness the potential of mechanical strength of thefiber.

REINFORCEMENT

The properties required for a particular application, alongwith other questions such as cost, define the fiber to be usedas reinforcement. The prerequisites for a given applicationdefine the fiber length, diameter, and the need for surfacemodifications of the fiber, among other characteristics.

Glass fibers are extensively used as reinforcement forphenolic-type matrices. These fibers are available in vari-ous forms such as E-glass, which is characterized by lowalkali content and good electrical, mechanical, and chem-ical properties; C-glass, which is chemical resistant; orS-glass, which has enhanced mechanical properties thatmeet the specifications for aerospace applications. Glassfibers can be produced as continuous strands or filamentswith different diameters, and this parameter, along withspecific density, is very important for health and safety,Respirability dictates whether the fibers pose an apprecia-ble hazard, which is mainly determined by diameter anddensity. A fiber with a certain diameter and a high specificdensity is associated with low respirability, and whetherit is hazardous is also related to the biopersistence of thefibers, according to the World Health Organization (WHO).

Carbon fibers (CFs) can be prepared by the controlledpyrolysis of organic precursors such as cellulose, pitch,polyacrylonitrile, and some phenolic fibers. The develop-ment of CFs was driven by the aerospace industry becauseof its properties, which are very suitable for the needsof this segment. CFs have low weight, high strength andhigh modulus, fatigue resistance and vibration damping,corrosion resistance, good friction and wear qualities, lowthermal expansion, and good thermal and electrical con-ductivity [54]. The adhesion between CFs and the phenolicmatrix can be improved through the modification of thefiber surface, for instance, by chemical or electrochemi-cal oxidation. Several groups may be introduced throughoxidation, depending on the solution used, but hydroxylgroups are generated for most solutions. Once hydroxylgroups are introduced on the surface of CFs, this func-tionalized surface may react with coupling agents, forinstance, glutaraldehyde, which is also reactive towardphenolic resin, increasing the adhesion at the fiber–matrixinterface [54].

Aramid corresponds to organic fibers produced fromaromatic polyamides, such as Kevlar. The adhesionbetween this fiber and resins, such as phenolics, is poormainly because of its high crystallinity. The interfacialadhesion between Kevlar fabric and the phenolic resincan be improved by treating the surface, for instance,with cold plasma, which has the advantage of modifyingthe surface without affecting the bulk properties of thematerial [55].

Compared to glass, carbon and aramid fiber-reinforcedmaterials have lower specific gravity, which favors them in



Table 1. Properties of Sugarcane Bagasse, Curaua, Coir, Jute, and Sisal Fibers

Fibers Sugarcane Bagassea Curauab Coirc Juted Sisale

Diameter (μm) 300–500 97 100–460 18–30 50–200Density (Kg/m3) 450–492 920 1390–1520 1450 1260–1330Microfibrillar angle (◦) 10–22 18.8 30–49 8.1 10–22Cellulose content (%) 55 73.6 43 58–63 65Crystallinity 47 67; 75.6 44 50 57; 72.2Hemicellulose content (%) 17 9.9 4 21–24 20Lignin content (%) f 25 7.5 48 12–15.9 12Tensile strength (MPa) 220 495 120 465 183Elongation (%) 1,1 1.3 8 0.7 1.0

aRefs 59,60,71–73.bRefs 57,60–62,71.cRefs 50,71,74.dRefs 57,64,71,74,75.eRefs 31,57,65,70,71,74.f Klason lignin.

automotive and aerospace applications due to the weightreduction when metal is replaced by these materials[56]. Depending on the properties required, fibers canbe mixed—such as glass, carbon, and aramid—renderinghybrid fabrics.

Agro-based fibers are of interest, considering thegrowing attention that these materials have aroused.Lignocellulosic fibers are particularly interesting asplastic reinforcements because of their low cost, lowdensity, process flexibility, and modest equipmentrequirement. These fibers are renewable, widely grown,moldable, anisotropic, nonabrasive, porous, viscoelastic,biodegradable, compostable, and reactive [57]. Lignocel-lulosic fibers have many hydroxyl groups on the surface,mainly from cellulose and lignin, which may interacteasily with the phenolic or lignophenolic polar matrices.

The large worldwide availability of vegetal fibers, theirlow cost, and their intrinsic properties have led to thesearch for alternative applications for these fibers besidesthe traditional uses such as textiles, paper production,and fuel [57]. The present urgent need to develop andcommercialize composite materials based on constituentsderived from renewable sources has had a great impacton the drive to reduce the dependence on nonrenewablematerials derived from fossil sources, both from environ-mental and economic viewpoints. Several enterprises havestarted to use composites reinforced with vegetal fibers,such as the automotive industry. Natural fibers are veryefficient in sound damping, are biodegradable, and can beobtained using 80% less energy [58].

One important aspect that must be considered for com-posites reinforced with vegetal fibers concerns fiber supplyregularity. In many countries, wood is the main source forfiber supply. Annual plants have the disadvantage of sea-sonal cropping over wood as fiber suppliers, which raisesthe need for subsequent cleaning, drying, storage, andother processes. In contrast, whereas a tree takes years togrow, annual plants have a full cycle in 12 months. The useof fibers to manufacture materials with high specifications,such as in composites, requires systematization of the pro-cesses from the plantation to the storage before being sold.The highly demanding market of the automotive industry

has already met these requirements [57]. With themarket growth, vegetal fibers for specific applications willprobably grow in distinct areas, which in turn can decreaseor eliminate the disadvantage of fiber supply irregularity.

Among vegetal fibers, sugarcane bagasse [59,60],curaua [60–62], coir [50,63], jute [57,64], and sisal[30,31,36,41,57,65–70] have been considered as rein-forcements for composites. Some of their properties areindicated in Table 1.

Curaua and jute fibers present the best mechanicalcharacteristics with low lignin and high cellulose contents,whereas coir fibers display low tensile strength with highelongation at break in relation to their high lignin content.The lignocellulosic fibers of non-wood plants appear to bevery well suited for composite material development in thereplacement of synthetic fibers, such as glass fibers.

Agro-Fibers and Composites

The mechanical performance of a fiber-reinforced matrixcomposite mainly depends on the strength and modu-lus of the fiber, the strength and chemical stability ofthe resin, and the effectiveness of the bond between theresin and fiber in transferring stress through the inter-face. An improvement of the interfacial properties shouldimprove the performance of the reinforced composites.Several disadvantages of natural fibers, such as mechani-cal and thermal degradation during processing, can makethem undesirable for certain applications. The thermaldegradation of the fibers occurs above 200◦C, resulting ingaseous products, which can cause high porosity and lowermechanical properties of the composites. This problemis considerably diminished for phenolic or lignopheno-lic resins because, in contrast to various thermoplasticmatrices such as polypropylene, the processing of phenolicthermosetting resins takes place at temperatures below200◦C. Moreover, the incompatibility between hydrophiliclignocellulosic fibers and hydrophobic thermoplastic poly-meric matrices, which is one of their main disadvantagesdue to a lack of adhesion between the fibers and the resinat the interface, is minimized when phenolic matrices areused because of the polar hydroxyl groups in their struc-ture. To produce composites with good properties, it is



necessary to promote improvements in the interface area.The use of coupling agents and chemical treatments of thefiber and/or matrix have been suggested in the literature[31,32,36,41,47,59–62,65,66,68,70,74,76,77].

A new method of chemically modifying the surfaceof lignocellulosic fibers has been recently developed[31,32,59,60,62,65,70]. This involves a selective modifi-cation of the lignin polymer that partly preserves thecellulose. The oxidation of the fibers involves a selectiveoxidation by sodium periodate and/or chlorine dioxide ofguaiacyl and syringyl units of lignin, generating ortho-and para-quinones and muconic derivatives able toreact with furfuryl alcohol (FA). This latter substancecan be easily obtained by reduction of furfural, whichis isolated from renewable sources. This method wasapplied to sugarcane, curaua, and sisal fibers. The resultsshowed that the FA-modified fibers had a thin coatingof poly(furfuryl alcohol) (PFA), indicating that the FApolymerization reaction had occurred. The PFA coatingformed after the treatments favored fiber/phenolic matrixinteractions at the interface, which increased the adhesionbetween the fibers and matrix polymer in compositesmaterials. Although ClO2 was reported to be safe forcellulosic fibers [78], the chemical treatments causedsome fiber degradation that affected the mechanicalproperties and decreased the impact strength of thecorresponding composites. It is likely that the chlorousacid (HClO2) formed by the action of ClO2 on lignin waspartly responsible for the fiber degradation [79].

Another way to increase the compatibility of the fiberwith the phenolic matrix is to treat the fibers using anaqueous alkali solution, which corresponds to a merceriza-tion of cellulose and a removal of hemicellulose and ligninbiopolymers [57,64]. The tensile strength of sisal andjute fibers increased by 58% and 27%, respectively, usingmercerization treatment in sodium hydroxide, whereastheir elongation at break increased by 40% and 129%,respectively [57,64]. SEM images of composites made withphenolic resins demonstrated that the alkali treatmentof fibers increased the fiber surface roughness and sepa-rated the fiber bundles, which facilitated the diffusion ofthe pre-polymer into the fiber network leading to a moreintense fiber–matrix interaction during the final cure step[57]. The alkali treatment should not be too strong so as toavoid deterioration of the fiber chains: for example, whenjute fibers were treated at 0◦C with 5% aqueous sodiumhydroxide for 0.5, 1, and 2 h, the composite displayed animpact strength of 40, 85, and 50 J/m, respectively [57].

The wettability of the fibers by the resins, depending onthe aggregation of fiber bundles, can be partially relatedto electrostatic interactions between fiber surfaces, whichin turn can be a consequence of the electronic migra-tion caused by the friction between the surfaces. In theinner part of an insulating material, such as lignocellulosicfibers, electron movement is limited, and this type of mate-rial may retain charges distributed on the surface. In theaqueous alkali treatment, these charges are neutralized.Another method to neutralize the electric charges is to sub-ject the material to ionized air [57,61,64]. In this case, thewettability of fibers will be improved using a dry method,which represents a substantial advantage in relation to the

treatment with an alkali aqueous solution (mercerization)that involves the laborious drying step of the hygroscopiclignocellulosic fibers. After ionized air treatment, the ten-sile strength of sisal and jute fibers increased by 23% and17%, respectively, whereas that of curaua fibers decreasedby 3%. The elongation at break increased for sisal, jute,and curaua fibers by 40, 86, and 7.7%, respectively [57].As for the alkali-treated fibers, the treatment should notbe too long so as to avoid deterioration of the fiber chains:for example, when curaua fibers were treated by ionizedair for 7 h, the composite impact strength increased from85 to 145 J/m (70.6% increase) and then decreased to110 J/m for 12 h of exposure [61]. SEM images of the frac-tured composites, after impact tests, showed many voidsin the matrix region. The impact strength of phenolicmatrices is affected by the formation of voids, which ismainly due to the vaporization of the water generatedduring the condensation reactions that occur during thecuring process. These microvoids can lead to microcrack-ing or stresses in the final molded composite. The numberof voids was minimized for composites reinforced withcuraua fibers, which were treated for 7 h with ionized air.This result was in part ascribed to a good penetration ofthe wet resin into the well-separated fiber bundles [61].

Sisal fibers appeared to be an important vegetal fiberto reinforce phenolic composites because of its abundantavailability and its excellent mechanical properties dueto a high cellulose content and crystallinity index. Recentstudies to increase the impact strength of the composite bychemically modifying the fibers with hydroxymethylatedlignin [66], benzophenonetetracarboxylic dianhydride [68],and hydroxy-terminated polybutadiene rubber [69] did notshow the expected effect, although fiber–resin interactionsat the interface were increased. Nonetheless, a decreaseof the composites’ hygroscopy was observed, which is animportant parameter for the development of such materi-als. Another important parameter to consider is the curecycle. It was shown for thermoset phenolic matrices rein-forced by sisal fibers [67] that the higher the values ofthe final pressure used at the point of the matrix cureconsolidation, the lower the amount of voids present in thecomposites. This characteristic was due both to a betterfiber–matrix interaction and to the filling of the fibers bythe matrix in the composite, as shown by SEM images.Good curing conditions can lead to a 10% increase in thevalue of impact strength and to an approximately 20%decrease in the amount of absorbed water when comparedto non-optimized curing conditions [67].

Composites based on phenolic-type matrices can bemanufactured by techniques such as hand laminating,spray depositing, resin injection, vacuum-assisted resintransfer, and press molding. The selection of a fabricationprocess for a certain phenolic-type composite depends on anumber of factors, such as the characteristics of reinforce-ment and fillers as well as the cost and/or performancerequired for the end use. In some applications, such as inaerospace, aircraft, and military structures, performanceis the main criterion, and normally the related compositesare manufactured using a prepreg (preimpregnated fibersand fabrics) molding process [56].



PHENOLIC NANOCOMPOSITES

In the area of polymeric composites, in the past decadesmuch attention has been directed to composites filled withnanofibers and/or nanoparticles. The research in this areawas considerably favored by the availability of scanningtunneling microscopy and scanning probe microscopy sincethe 1980s. The large-scale production of polymer nanocom-posites has benefited form the fact that, in many cases,similar processes can be used for both conventional andnano composites [80].

The boom observed in nanotechnology in recentdecades has reached the phenolic composites as well and,although a reasonable level of development has alreadybeen achieved, it can be expected that major advances willstill occur in the near future in the area of nanocompositesbased on phenolic-type matrices.

The use of nanofibers or nanoparticles as reinforcementcan improve several properties of the related composite,such as thermal, flame, chemical, and moisture resistance,as well as decreased permeability [27], among others asmentioned below.

In general, intercalated and exfoliated compositescan be found in polymer-layered silicate nanocomposites(PLSNs). Intercalated composites are obtained whenmacromolecules are inserted into the galleries (i.e., in thenanometric-scale space that exists between the layers),and exfoliated composites are obtained when there is adisruption of layers due to a delamination process andthe galleries are expanded, allowing the dispersion ofsilicate nanolayers in the polymeric matrices. Nanoclayscan be used to reinforce phenolic matrices without anymodification because phenolics have polar groups thatfavor the interactions with this kind of nanoparticle.In addition, the medium in which the polymerizationis conducted (aqueous solution) favors the exfoliation ofnanoclay particles by in situ polymerization, which inturn increases the matrix–reinforcement interactionswhen compared to intercalated composites [81].

The performance of polybenzoxazine was improvedwhen clay nanocomposites were prepared. Montmoril-lonite (MMT) which was organically modified (OMMT)was used to prepare polybenzoxazine/clay nanocompositesby both melt and solvent methods. A complete exfolia-tion of clay nanolayers into the polybenzoxazine matrixwas attained when the melt method was used and whenN-methyl-2-pyrrolidone (NMP) was used as the solvent.The inclusion of clay improved the thermal stability ofpolybenzoxazine [82].

Owing to the ability of phenolic resins to form charduring endothermic pyrolysis, composites based on thismaterial, normally reinforced with rayon-based carbonfabric, are applied as ablative material for rocket nozzles[83]. To reduce the overall weight of aerospace systems,carbon nanofibers (CNFs) can be used as additives in phe-nolic resins. Resole phenolic matrix with a high contentof CNF showed excellent high temperature erosion resis-tance in plasma torch tests at 1650◦C, which can be con-sidered as materials highly appropriate for rocket nozzleapplications. In addition, these composites (CNF/phenolicresin) are also considered as precursors for carbon–carbon

composites (CCC) [84], which are normally prepared forhigh temperature applications [2].

The CNF can form aggregates owing to attractive forces,which can considerably decrease the mechanical proper-ties of the composites because the dispersion of CNFs inresin is affected. Therefore, disaggregating these agglom-erates, when in contact with the resin, is one of the keypoints while preparing CNF-reinforced phenolic compos-ites with excellent properties. Besides other factors, suchas the curvature of fibers, the disaggregation is highlydependent on the relative surface energy of both CNFsand the resin. To improve the compatibility between CNFsand phenolic resins, the surface of the fibers can be mod-ified. The oxidation of CNF by nitric acid can introducesurface functionality (ester, anhydride, quinoid, and phe-nolic hydroxyl functions), which in turn increases theCNF–phenolic resin compatibility, thus favoring the dis-aggregation and dispersion of fibers in resin [84].

Nanoparticles can be combined with other reinforce-ments to reinforce phenolic matrices, leading to hybridcomposites. The friction and wear behavior of carbonfabric-reinforced polymer (CFRP) composites can beimproved by SiO2 sol deposition on the fabric surface.Zhanga et al. [85] found that the nanostructured SiO2thin film obtained from this process strengthened theadhesion between the fiber and phenolic matrix, thusimproving the friction-reduction and antiwear propertiesof CFRP composites [85].

RECYCLING

Recycling at the end of the life cycle of thermoset compos-ite materials, such as those prepared from phenolic-typeresins, is not an easy matter but requires increased atten-tion because of environmental issues, which can slow thedevelopment or even prevent the use of these materialsin some markets. The incineration of wasted compositesnot always is a good option because the process can be asource of pollution [86,87].

The crosslinking of thermosetting polymers, such asphenolics, prevents their melting and remolding, as occurswith thermoplastics. When these thermosetting polymerscorrespond to matrices of composites, the recyclinginvolves the additional issue concerning the presence offibers and, in some cases, fillers [86].

In general, two technologies are used for recyclingthermoset composites: mechanical recycling (materials areground to reduce the size of the scrap, producing powderedor fibrous products) or thermal processes (materials andenergy are produced from the scrap) [86,87]. Particulatematerial obtained from phenolic composites containingglass or CF can be used as fillers and extenders in moldingcompounds, generating materials with properties similarto the composites in which virgin materials are used [87].

Indeed, the most appropriate method of recyclingshould be sought for each particular case of phenolic-typematrix composite, and one should also consider the natureof the fibers and reinforcements present. In this context,Nagamatsu and Funaoka [88] have used lignophenols(LPs) to prepare lignin-based recyclable composites, and



they showed that, under alkaline conditions and using theswitching functionality of LPs, the LP fractions and othercomponents of the composites can be reseparated [88].

REFERENCES

1. Baekeland LH, Ind J. Eng Chem 1909;1:149; Production ofbakelite. US 942,699. 1909.

2. Pilato LA, Koo JH, Wissler GE, et al. A review—phenolic andrelated resins and their nanomodification into phenolic resinfiber reinforced plastic systems. J Adv Mater 2008;40:5–16.References therein.

3. Lewark BA. Composites: past, present future: phe-nolics revisited. Compos Technol 2007; http://www.compositesworld.com/articles/ct. Accessed 2010 Nov 11.

4. Gardziella A, Pilato LA, Knop A. Phenolic resins, chemistry,applications, standardization, safety, and ecology. 2nd ed.Berlin: Springer; 2000. ISBN: 3540655174.

5. Ghosh NN, Kiskan B, Yagci Y. Polybenzoxazines. New highperformance thermosetting resins: synthesis and properties.Prog Polym Sci 2007;32:1344–1391.

6. Mimms A, Kocurek MJ, Pyatte JA, et al. Kraft pulping.Atlanta: Tappi Press; 1997. ISBN: 0898523222.

7. Donohoe BS, Decker SR, Tucker MP, et al. Visualizinglignin coalescence and migration through maize cell wallsfollowing thermochemical pretreatment. Biotechnol Bioeng2008;101:913–925.

8. Keshwani DR, Cheng JJ. Modeling changes in biomasscomposition during microwave-based alkali pretreatment ofswitchgrass. Biotechnol Bioeng 2010;105:88–97.

9. Lee SH, Doherty TV, Linhardt RJ, et al. Ionic liquid-mediatedselective extraction of lignin from wood leading toenhanced enzymatic cellulose hydrolysis. Biotechnol Bioeng2009;102:1368–1376.

10. Sellers T, Lora JH, Okuma M. Organosolv-lignin-modifiedphenolics as strandboard binder. 1. organosolv ligninand modified phenolic resin. Mokuzai Gakkaishi1994;40:1073–1078.

11. Lawther JM, Sun RC, Banks WB. Characterization of dis-solved lignins in two-stage organosolv delignification of wheatstraw. J Wood Chem Technol 1996;16:439–457.

12. Lora JH, Glasser WG. Recent industrial applications of lignin:a sustainable alternative to nonrenewable materials. J PolymEnviron 2002;10:39–48.

13. Wang MC, Leitch M, Xu CB. Synthesis of phenol-formaldehyde resole resins using organosolv pine lignins.Eur Polym J 2009;45:3380–3388.

14. Hernandez-Salas JM, Villa-Ramırez MS, Veloz-Rendon JS,et al. Comparative hydrolysis and fermentation of sugarcaneand agave bagasse. Bioresour Technol 2009;100:1238–1245.

15. Zhang B, Keitz MV, Valentas K. Maximizing the liq-uid fuel yield in a biorefining process. Biotechnol Bioeng2008;101:903–912.

16. Ewanick SM, Bura R, Saddler JN. Acid-catalyzed steampretreatment of lodgepole pine and subsequent enzymatichydrolysis and fermentation to ethanol. Biotechnol Bioeng2007;98:737–746.

17. Sanchez OJ, Cardona CA. Trends in biotechnological pro-duction of fuel ethanol from different feedstocks. BioresourTechnol 2008;99:5270–5295.

18. Sixta H, Harms H, Dapia S, et al. Evaluation of neworganosolv dissolving pulps. Part I: preparation, analytical

characterization and viscose processability. Cellulose 2004;11:73–83.

19. Fink HP, Weigel P, Ganster J, et al. Evaluation of neworganosolv dissolving pulps. Part II: structure and NMMOprocessability of the pulps. Cellulose 2004;11:85–98.

20. Pan X, Xie D, Yu RW, et al. The bioconversion of mountainpine beetle-killed lodgepole pine to fuel ethanol using theorganosolv process. Biotechnol Bioeng 2008;101:39–48.

21. Pan X, Arato C, Gilkes N, et al. Biorefining of softwoodsusing ethanol organosolv pulping: preliminary evaluation ofprocess streams for manufacture of fuel-grade ethanol andco-products. Biotechnol Bioeng 2005;90:473–481.

22. Pan X, Gilkes N, Kadla J, et al. Bioconversion of hybrid poplarto ethanol and co-products using an organosolv fractionationprocess: optimization of process yields. Biotechnol Bioeng2006;94:851–861.

23. Brosse N, Sannigrahi P, Ragauskas A. Pretreatment of Mis-canthus x giganteus using the ethanol organosolv process forethanol production. Ind Eng Chem Res 2009;48:8328–8334.

24. Pye EK, Lora JH. The Alcell process, a proven alternative tokraft pulping. Tappi J 1991;74:113–118.

25. Frederick WJ, Lien SJ, Courchene CE, et al. Co-productionof ethanol and cellulose fiber from southern pine: atechnical and economic assessment. Biomass Bioenergy2008;32:1293–1302.

26. Mansouri NE, Salvado J. Analytical methods for determiningfunctional groups in various technical lignins. Ind Crops Prod2007;26:116–124.

27. Pilato L. Phenolic resins: a century of progress. Berlin,Heildelberg: Springer-Verlag; 2010. ISBN: 9783642047138.

28. Fengel D, Wegener G. Wood: chemistry, ultrastructure, reac-tions. New York: Walter de Gruyter; 1989. ISBN: 3110120593

29. Rowell RM, Han SJ. Characterization and factors affect-ing fiber properties. In: Frollini E, Leao AL, Mattoso LHC,editors. Natural polymers and agrofibers based composites.Sao Paulo: USP/UNESP/EMBRAPA; 2000. pp 25–48. ISBN:858646306X.

30. Ramires EC, Megiatto JD, Gardrat C, et al. Valorization of anindustrial organosolv-sugarcane bagasse lignin: characteri-zation and use as a matrix in biobased composites reinforcedwith sisal fibers. Biotechnol Bioeng 2010;107:612–619.

31. Paiva JMF, Frollini E. Unmodified and modified surface sisalfibers as reinforcement of phenolic and lignophenolic matri-ces composites: thermal analyses of fibers and composites.Macromol Mater Eng 2006;291:405–417.

32. Hoareau W, Oliveira FB, Grelier S, et al. Fiberboards basedon sugarcane bagasse lignin and fibers. Macromol Mater Eng2006;291:829–839.

33. Malutan T, Nicu R, Popa VI. Contribution to the study ofhydroxymethylation reaction of alkali lignin. BioResources2008;3:13–20.

34. Campana Filho SPC, Frollini E, Curvelo AAS. Organosolvdelignification of lignocellulosic materials: preparation andcharacterization of lignin and cellulose derivatives. In: LeaoAL, Carvalho FX, Frollini E, editors. Lignocellulosic-plasticcomposites. Brazil: USP and UNESP; 1997. p 163–178.

35. Doherty W, Halley P, Edye L, et al. Studies on polymers andcomposites from lignin and fiber derived from sugar cane.Polym Adv Technol 2007;18:673–678.

36. Ramires EC, Megiatto JD, Gardrat C, et al. Biobased compos-ites from glyoxal-phenolic resins and sisal fibers. BioresourTechnol 2010;101:1998–2006.



37. Pizzi A, Orovan E, Cameron FA. The development of weatherand boil-proof phenol-resorcinol-furfural cold-setting adhe-sives. Holz als Roh und Werkstoff 1984;42:467–472.

38. Gandini A, Belgacem NM. Furan in polymer chemistry. ProgPolym Sci 1997;22:1203–1379.

39. Pizzi A, Pasch H, Simon C, et al. Structure of resorcinol,phenol, and furan resins by Maldi-Tof mass spectrometryand 13C NMR. J Appl Polym Sci 2004;92:2665–2674.

40. Pizzi A. Advanced wood adhesives technology, New York:Marcel Dekker; 1994. ISBN: 0824792661.

41. Oliveira FB, Gardrat C, Enjalbal C, et al. Phenol—furfuralresins to elaborate composites reinforced with sisalfibers—molecular analysis of resin and properties of com-posites. J Appl Polym Sci 2008;109:2291–2303.

42. Mattioda G, Metivier B, Guette JP. Le glyoxal, une moleculetres fonctionnelle. II. Utilisations industrielles. L’ActualiteChimique. juin-juillet; 1982. pp 33–40.

43. Ballerini A, Despres A, Pizzi A. Non-toxic, zero emissiontannin—glyoxal adhesives for wood panels. Holz als Roh undWerkstoff 2005;63:477–478.

44. El Mansouri NE, Pizzi A, Salvado J. Lignin-based wood paneladhesives without formaldehyde. Holz als Roh und Werkstoff2007;65:65–70.

45. El Mansouri NE, Pizzi A, Salvado J. Lignin-based poly-condensation resins for wood adhesives. J Appl Polym Sci2007;103:1690–1699.

46. Hirayama T, Yamada N, Nohara M, et al. The high perfor-mance liquid chromatographic determination of total malon-dialdehyde in vegetable oil with dansyl hydrazine. J Sci FoodAgric 1984;35:338–344.

47. Ramires EC, Megiatto JD, Gardrat C, et al. Biobased compos-ites from glyoxal-phenol matrices reinforced with microcrys-talline cellulose. Polimeros 2010;20:126–133.

48. Wrzesniewska-Tosik K, Tomaszewski W, Strusczyk H. Man-ufacturing and thermal properties of lignin based resins. FibText East Eur 2001;33:50–53.

49. Tondi G, Pizzi A. Tannin-based rigid foams: characterizationand modification. Ind Crops Prod 2009;29:356–363.

50. Barbosa V, Ramires EC, Razera IA, et al. Biobased compositesfrom tannin-phenolic polymers reinforced with coir fibers. IndCrops Prod 2010;32:305–312.

51. Vazquez G, Gonzalez-Alvarez J, Antorrena G. Curing of aphenol—formaldehyde tannin adhesive in the presence ofwood. J Therm Anal Calorim 2006;84:651–654.

52. Lei H, Pizzi A, Du G. Environmentally friendly mixed tan-nin/lignin wood resins. J Appl Polym Sci 2008;107:203–209.

53. Taylor JG. Composites. In: Pilato L, editor. Phenolic resins:a century of progress. Berlin, Heildelberg: Springer-Verlag;2010, Chapter 12. p. 263. ISBN: 9783642047138.

54. Choi MH, Jeon BH, Chung IJ. The effect of coupling agent onelectrical and mechanical properties of carbon fiber/phenolicresin composites. Polymer 2000;41:3243–3252. referencestherein.

55. Guo F, Zhang Z, Liu W, et al. Effect of plasma treatmentof Kevlar fabric on the tribological behavior of Kevlar fab-ric/phenolic composites. Tribol Int 2009;42:243–249.

56. Koizumi K, Charles T, De Keyser H. Phenolic moldingcompounds. In: Pilato L. Phenolic resins: a century ofprogress. Berlin, Heildelberg: Springer-Verlag; 2010, Chapter16. ISBN: 9783642047138.

57. Frollini E, Paiva JMF, Trindade WG, et al. Plastics andcomposites from lignophenols In: Wallenberger FT, WestonN, editors. Natural fibers, polymer and composites—recent

advances. Norwell, MA: Kluwer Academic Publishers; 2004;Chapter 12. pp 194–225, ISBN 1 4020 7643.

58. Mohanty AK, Wibowo A, Misra M, et al. Effect of processengineering on the performance of natural fiber reinforcedcellulose acetate biocomposites. Compos A Appl Sci Manuf2004;35:363–370.

59. Trindade WG, Hoareau W, Razera IAT, et al. Phenolic ther-moset matrix reinforced with sugarcane bagasse fibers:attempt to develop a new fiber surface chemical modificationinvolving formation of quinones followed by reaction withfurfuryl alcohol. Macromol Mater Eng 2004;289:728–736.

60. Trindade WG, Hoareau W, Megiatto JD, et al. Thermoset phe-nolic matrices reinforced with unmodified and surface-graftedfurfuryl alcohol sugarcane bagasse and curaua fibers:properties of fibers and composites. Biomacromolecules2005;6:2485–2496.

61. Trindade WG, De Paiva JMF, Leao AL, et al. Ionized-air-treated curaua fibers as reinforcement for phenolic matri-ces. Macromol Mater Eng 2008;293:521–528.

62. Hoareau W, Trindade WG, Siegmund B, et al. Sugarcanebagasse and curaua lignins oxidized by chlorine dioxide andreacted with furfuryl alcohol: characterization and stability.Polym Degrad Stab 2004;86:567–576.

63. Monteiro SN, Terrones LAH, D’Almeida JRM. Mechanicalperformance of coir fiber/polyester composites. Polym Test2008;27:591–595.

64. Razera IAT, Frollini E. Composites based on jute fibers andphenolic matrices: properties of fibers and composites. J ApplPolym Sci 2004;91:1077–1085.

65. Megiatto JD, Oliveira FB, Rosa DS, et al. Renewableresources as reinforcement of polymeric matrices: compos-ites based on phenolic thermosets and chemically modifiedsisal fibers. Macromol Biosci 2007;7:1121–1131.

66. Megiatto JD, Silva CG, Rosa DS, et al. Sisal chemically modi-fied with lignins: correlation between fibers and phenolic com-posites properties. Polym Degrad Stab 2008;93:1109–1121.

67. Megiatto JD, Silva CG, Ramires EC, et al. Thermosetmatrix reinforced with sisal fibers: effect of the cure cycleon the properties of the biobased composite. Polym Test2009;28:793–800.

68. Botaro VR, Siqueira G, Megiatto JD, et al. Sisal fibers treatedwith NaOH and benzophenonetetracarboxylic dianhydrideas reinforcement of phenolic matrix. J Appl Polym Sci2010;115:269–276.

69. Megiatto JD, Ramires EC, Frollini E Jr. Phenolic matricesand sisal fibers modified with hydroxy terminated polybuta-diene rubber: impact strength, water absorption, and mor-phological aspects of thermosets and composites. Ind CropProd 2010;31:178–184.

70. Megiatto JD, Hoareau W, Gardrat C, et al. Sisal fibers: surfacechemical modification using reagent obtained from a renew-able source; characterization of hemicellulose and lignin asmodel study. J Agric Food Chem 2007;55:8576–8584.

71. Satyanarayana KG, Guimaraes JL, Wypych F. Studies onlignocellulosic fibers of Brazil. Part I: source, production,morphology, properties and applications. Compos A Appl SciManuf 2007;38:1694–1709.

72. Ghazali MJ, Azhari CH, Abdullah S, et al. Characterizationof natural fibers (sugarcane bagasse) in cement composites.Proc World Cong Eng Lond 2008;2:1307–1309.

73. Saw SK, Datta C. Jute/bagasse composites. BioResources2009;4:1455–1476.

74. Geethamma VG, Mathew KT, Lakshminarayanan R, et al.Composite of short coir fibres and natural rubber: effect


2068 PHTHALOCYANINE MATRIX RESINS AND COMPOSITES

of chemical modification, loading and orientation of fibre.Polymer 1998;39:1483–1481.

75. Ahmed Z, Haque MS, Akhter F, et al. Study of the chemicalcomposition of different pipeline varieties of jute fibers. PakJ Biol Sci 2003;6:1463–1467.

76. Li B, Thielemans W, Dufresne A, et al. Surface functionaliza-tion of cellulose fibres and their incorporation in renewablepolymeric matrix. Compos Sci Technol 2008;68:3193–3201.

77. Li Y, Pickering KL, Farrell RL. Analysis of green hemp fiberreinforced composites using bag retting and white rot fungaltreatments. Ind Crops Prod 2009;29:420–426.

78. Lemeune S, Jameel H, Chang HM, et al. Effect of ozone andchlorine dioxide on the chemical properties of cellulose fibers.J Appl Polym Sci 2004;93:1219–1223.

79. Hubbell CA, Ragauskas AJ. Effect of acid-chlorite delignifica-tion on cellulose degree of polymerization. Bioresour Technol2010;101:7410–7415.

80. Hussain F, Hojjati M. Review article: polymer-matrixnanocomposites, processing, manufacturing, and application:an overview. J Compos Mater 2006;40:1511–1575.

81. Zhou G, Movva S, Lee LJ. Nanoclay and long-fiber-reinforcedcomposites based on epoxy and phenolic resins. J Appl PolymSci 2008;108:3720–3726.

82. Takeichi T, Agag T. High performance polybenzoxazines asnovel thermosets. High Perform Polym 2006;18:777–797.

83. Srikanth I, Daniel A, Kumar S, et al. Nano silica modifiedcarbon–phenolic composites for enhanced ablation resistance.Scr Mater 2010;63:200–203.

84. Yoonessi M, Toghiani H, Wheeler R, et al. Neutron scat-tering, electron microscopy and dynamic mechanical stud-ies of carbon nanofiber/phenolic resin composites. Carbon2008;46:577–588. references therein

85. Zhanga X, Pei X, Zhang J, et al. Effects of carbon fiber surfacetreatment on the friction and wear behavior of 2D woven car-bon fabric/phenolic composites. Colloids Surf A PhysicochemEng Asp 2009;339:7–12.

86. Pickering SJ. Recycling technologies for thermoset compos-ite materials—current status. Compos A Appl Sci Manuf2006;37:1206–1215. references therein

87. Mazumdar SK. Recycling of composites. Composites manu-facturing: materials, product and process engineering. CRCPress; 2002, Chapter 12, and references therein. ISBN:9783642047138.

88. Nagamatsu Y, Funaoka M. Design of recyclable matrices fromlignin-based polymers. Green Chem 2003;5:595–601.

PHTHALOCYANINE MATRIX RESINSAND COMPOSITES

ROBERT Y. TINGNaval Research Laboratory,

Orlando, FL

Fiber-reinforced composite materials are being consideredfor many advanced structural applications in order toachieve a substantial weight saving in the structures.

Adapted from Phthalocyanine Matrix Resins and Composites,First Edition.

Many of these applications involve a high temperaturerequirement that cannot be met by conventional matrixresin systems such as epoxy. For instance, in the design ofadvanced vertical and short takeoff and landing (V/STOL)aircraft, many of the metallic structural components mustbe replaced with organic composites for weight-savingpurposes in order to compensate for the large and heavypropulsive systems required for vertical lift. By incorporat-ing the superior properties of fiber-reinforced composites,such as high strength-to-weight ratio and fatigue resis-tance, the designer may successfully develop a V/STOLaircraft with extended range and/or increased payload.The proposed design calls for a matrix resin that can meetoperational temperatures in excess of 200◦C. In addition,the resin needs to have a very low moisture sensitivity.Unfortunately, conventional epoxy resins can only offer amaximum use temperature of about 135◦C, and the mois-ture absorption in these resins is normally quite high. Theroom temperature storage stability of the epoxies is alsovery poor.

In order to meet the requirement for a wide rangeof high temperature applications, such as adhesives,sealants, coatings, and matrix resins, research efforts ofGriffith and coworkers [1,2] at the Chemistry Division,Naval Research Laboratory in the 1970s have led tothe development of a new class of resins called phthalo-cyanines. These materials have been demonstrated tobe promising candidates for advanced composite appli-cations. In this article, the structure and properties ofphthalocyanine resins are discussed. The developmentof a selected phthalocyanine resin for fiber-reinforcedcomposites is also described. Test results on the mechan-ical properties of composite samples are presented andcompared with those of other popular composite systems.

MATERIAL

The chemistry of phthalocyanine resin synthesis and poly-merization was first reported by Griffith et al. [1]. Briefly,the reaction of 4-aminophthalonitrile with aliphatic diacidchlorides forms resin monomers that have a diamidestructure:

Abbreviated names are used to identify these com-pounds. For example, if n = 8, the compound is calledC-10 diamide because it was made from a diacid chloridecontaining 10 carbon atoms. Polymerization occurs onthermal reaction of the diamide monomers at tempera-tures above their melting temperatures. The B stage and

Documents

PHENOLIC RESINS AND COMPOSITES PHENOLIC COMPOSITES ...€¦ · pure fuel and as a gasoline enhancer [16,17]. The process in general consists of the hydrolysis of a lignocellulosic