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Effects Polyamide 6 Incorporation to the Short Glass Fiber Einforced ABS Composites Guralp

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The properties of 30 wt% short glass fiber (SGF) reinforced acrylonitrile-butadiene-styrene (ABS) terpolymer and polyamide 6 (PA6) blends prepared with extrusion were studied using the interfacial adhesion approach. Work of adhesion and interlaminar shear strength values were calculated respectively from experimentally determined interfacial tensions and short beam flexural tests. The adhesion capacities of glass fibers with different surface treatments of organosilanes were evaluated. Among the different silanes tested, g-aminopropyltrimethoxysilane (APS) was found to be the best coupling agent for the glass fibers, possibly, because of its chemical compatibility with PA6. Tensile test results indicated that increasing amount of PA6 in the polymer matrix improved the strength and stiffness of the composites due to a strong acid–base interaction at the interface. Incorporation of PA6 to the SGF reinforced ABS reduced the melt viscosity, broadened the fiber length distributions and increased the toughness of the composites. Fractographic analysis showed that the incorporation of PA6 enhanced the interactions between glass fibers and the polymeric matrix.
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  Effects of polyamide 6 incorporation to the short glass fiber reinforcedABS composites: an interfacial approach Guralp Ozkoc a , Goknur Bayram b, *, Erdal Bayramli c a  Department of Polymer Science and Technology, Middle East Technical University, 06531 Ankara, Turkey b  Department of Chemical Engineering, Middle East Technical University, 06531 Ankara, Turkey c  Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey Received 14 May 2004; received in revised form 4 September 2004; accepted 13 October 2004Available online 28 October 2004 Abstract The properties of 30 wt% short glass fiber (SGF) reinforced acrylonitrile-butadiene-styrene (ABS) terpolymer and polyamide 6 (PA6)blends prepared withextrusion were studiedusing the interfacial adhesion approach. Work ofadhesion and interlaminar shear strength valueswere calculated respectively from experimentally determined interfacial tensions and short beam flexural tests. The adhesion capacities of glass fibers with different surface treatments of organosilanes were evaluated. Among the different silanes tested,  g -aminopropyltrimethoxy-silane (APS) was found to be the best coupling agent for the glass fibers, possibly, because of its chemical compatibility with PA6. Tensiletest results indicated that increasing amount of PA6 in the polymer matrix improved the strength and stiffness of the composites due to astrong acid–base interaction at the interface. Incorporation of PA6 to the SGF reinforced ABS reduced the melt viscosity, broadened the fiberlength distributions and increased the toughness of the composites. Fractographic analysis showed that the incorporation of PA6 enhancedthe interactions between glass fibers and the polymeric matrix. q 2004 Elsevier Ltd. All rights reserved. Keywords:  Interface; ABS; Glass fiber reinforcement 1. Introduction The incorporation of fibrous glass is known to improvethe properties of the thermoplastic materials by applyingtraditional processes such as extrusion and injectionmolding [1–4]. The mechanical performance of glass fiberreinforced composites depends on not only the properties of individual components but also the interfacial interactionsestablished between the reinforcing agent and the matrixmaterial [5–9].An effective interface can be obtained if there existssufficient bonding between constituents. Silane couplingagents, which are generally applied to the surface of inorganic fillers, are well known and most widely used asinterfacial agents to bind glass fibers to polymeric matrices[10]; however, in some cases because of the lack of functional groups of polymers that allow reactions at theinterface, silane coupling agents are incapable of bindingthe fibers to polymers. One of the well-known solutions tothis problem is the introduction of new functional groupsexternally to the polymer. It has been reported by manyresearchers that to introduce polarity or acidity to a non-polar matrix, great variety of acidic additives includingacrylic acid, methacrylic acid, maleic acid and theiranhydrides have been used to enhance the adhesion betweenglass fibers and polymers [11]. The most commonly appliedprocess is the melt blending of reactive species, especiallythrough reactive extrusion [12].Acrylonitrile-butadiene-styrene (ABS) terpolymer gainsindustrial and scientific importance due to its toughness,dimensional stability and good surface appearance. Theprevious studies showed that incorporation of short glassfibers (SGF) to neat ABS to balance the toughness andstiffness results in an improvement in tensile strength and 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.polymer.2004.10.026Polymer 45 (2004) 8957–8966www.elsevier.com/locate/polymer* Corresponding author. Tel.:  C 90 312 210 2632; fax:  C 90 312 2101264. E-mail address:  gbayram@metu.edu.tr (G. Bayram).  modulus, on the other hand, a decrease in toughness isobserved. In addition to that, microscopic studies showedlack of adhesion between ABS and glass fibers [1,13,14].The current study focuses on the effects of incorporationof acidic groups by blending of ABS with polyamide 6(PA6) for functionalization of the polymeric matrix to bereinforced with SGFs; so that an improved interfacialadhesion between fiber and polymer can be established. Thestudy also includes a comparison of neat-ABS and PA6incorporated-ABS, which are reinforced with SGFs. At thebeginning, the adhesion capacities of the different couplingagents at the fiber/matrix interface were experimentallyexamined. The coupling agent, which exhibited the bestadhesion performance, was used for compounding SGFswith the polymeric matrices in the study that follows. 2. Background The bonding of glass fibers to polymer matrices has beenrecognized since glass fibers were first used in composites[10]. Organosilicone compounds (or silane coupling agents)are generally used for this purpose since the silicone endsare chemically similar to the structure of glass, and theorganic groups on the silicone are potentially capable of interacting with polymer [15].The reactions of silane coupling agent promoting theinterfacial adhesion are represented in Fig. 1 in whichtrialkoxysilane hydrolyzes in aqueous media to form asilanol compound, then, silanol reacts with the hydroxylgroup of the glass surface. The coupling reaction occursduring processing between glass fibers functionalized byorgano-functional silane and polymer, if it is chemicallyfavorable. ‘R’ is the organic functional group to interactwith the functionality of polymer ‘*R’.For a better understanding of fiber/matrix interphasemechanics, it is necessary to determine the interfacialstrength and possible interactions between polymer andfiber. This is usually carried out by means of contact anglemeasurements [9,16,17] to determine the thermodynamicalenergy of adhesion and specific mechanical tests on real ormodel composites to determine the strength of interphaseformed between fiber and polymer [18].The method of estimating the thermodynamical adhesionat fiber matrix interphase, which is generally called work of adhesion, from the surface properties of both materials, is atheoretical approach. This thermodynamical model of adhesion is certainly the most widely used approach inadhesion science. It considers that the adhesive will adhereto the substrate because of interatomic and intermolecularforces established at the interphase, provided that anintimate contact between both materials is achieved [19].The total surface energy,  g TOT i  , of a given non-metallicmaterial ( i ) can be considered as being composed of twoparts: the Liftshitz-van der Waals (LW),  g LW i  , and the acid–base (AB) component,  g AB i  [9,21]. This is written as the sumof the two components, g TOT i  Z g LW i  C g AB i  (1)where the acid–base term is a property based on the mutualinteraction of two unlike species, an acid and a base.  g AB i  iscomposed of two surface parameters:  g C i  , the Lewis acidcomponent and  g K i  is the Lewis base component of thesurface free energy. These, together, yield the acid–basecomponent of surface free energy,  g AB i  . g AB i  Z 2 ð g C i  g K i  Þ 1  =  2 (2)The most characteristic feature of these Lewis acid andbase components is their non-additivity. That is to say, if  Fig. 1. Reactions of organosilanes (R and *R are the functionalities of silane coupling agent and polymer, respectively). G. Ozkoc et al. / Polymer 45 (2004) 8957–8966  8958  phase ( i ) possesses only  g C i  or  g K i  , this component does notparticipate in the total surface free energy of the phase ( i ).However, it will interact with the complementary com-ponent (  j ) of the contacting phase.The values of   g AB i  ,  g C i  and  g K i  can be determined byusing the contact angle,  q  and ‘Complete Young Equation’[9,20], ð 1 C cos  q Þ g TOT i Z 2 ½ð g LW i  g LW  j  Þ 1  =  2 C ð g C i  g K  j  Þ 1  =  2 C ð g K i  g C  j  Þ 1  =  2   (3)The LW component of a solid surface ( i ) can also befound from the contact angle of a non-polar liquid (  j ), where g TOT  j  Z g LW  j  , on the solid surface. In this case, Eq. (3)reduces to, ð 1 C cos  q Þ g TOT  j  Z 2 ð g LW  j  g LW i  Þ 1  =  2 (4)As a result, the LW component of a solid surface can becalculated by determining the contact angle of a non-polarliquid on the solid surface in Eq. (4).For a bipolar liquid (L) contacting with the solid (S), withsurface tension  g L , acidic and basic surface parameters  g C L and  g K L , respectively, and non-polar surface component, g LWL  , the corresponding complete equation is as follows, ð 1 C cos  q L Þ g TOTL Z 2 ½ð g LWL  g LWS  Þ 1  =  2 C ð g C L  g K S  Þ 1  =  2 C ð g K L  g C S  Þ 1  =  2   (5)This is also written for a second bipolar liquid. A set of twosimultaneous equations are formed in terms of theparameters of the solid,  g K S ,  g C S  and two advancing contactangles  q 1  and  q 2 , which are measured on the solid surface.These two equations are then simultaneously solved for  g K S and  g C S  provided that the  g LW i  ,  g C i  and  g K i  for the probeliquids are known [21].Providing the known surface components of the contact-ing phases (i.e. polymer and fiber), the work of adhesion( W  a ) between phase 1 and phase 2 can be calculated fromthe summation of dispersive and acid/base components byusing [20], W  TOTa  Z W  LWa  C W  ABa Z 2 ½ð g LW1  g LW2  Þ 1  =  2 C ð g C 1  g K 2  Þ 1  =  2 C ð g K 1  g C 2  Þ 1  =  2   (6)The strength of interphase formed can be determined byapplying some specific mechanical tests on model or realcomposites systems. ‘Short Beam Flexural Test’ is astandard testing method to evaluate the interlaminar shearstrength (ILSS) of fiber reinforced composites [22]. Themeasurement is performed applying a three point bendingtest on a short beam with the span-to-depth ratio chosen toproduce interlaminar shear failure. For a rectangular cross-section, the apparent interlaminar shear strength,  t ILSS , isgiven by t ILSS Z 0 : 75  F bd   (7)where  F   is the rupture force under bending force,  b  is thewidth and  d   is the thickness of the specimen. 3. Experimental 3.1. Materials Information on materials used in this study aresummarized in Table 1. ABS, PA6 and glass fibers wereobtained from Emas Plastik, Tekno Polimer, and Cam Elyaf Glass Fiber companies, respectively. Silane coupling agentsused during surface modification of glass fibers were  g -aminopropyltrimethoxysilane (‘APS’ hereafter, AldrichChemical Co.),  g -(trimethoxysilyl)propylmethacrylate(‘MPS’ hereafter, Aldrich Chemical Co.), and a blend of styrylsilane and methacrylosilane, which had already beenapplied to the glass fibers by Cam Elyaf company, themanufacturer, (‘As received’ hereafter). 3.2. Experimental procedure Before new coupling agents were applied onto glass fibersurfaces, initial film formers and couplings had to beremoved. The removal was carried out in a furnace byburning off them at approximately 600  8 C for 30 min, thenby using a soxhlet apparatus glass fibers were washed withacetone for 1 h to remove organic degradation deposits.At first, solutions including 1 wt% coupling agent wereprepared with distilled water for hydrolysis. The pH of thesolution was adjusted to 4.5 with acetic acid to catalyze theMPS reaction. For APS, to avoid the possible reactionbetween amino group and acid, no catalyst was used. Sincethe MPS is not water soluble, it was dissolved in a solutionof 10 wt% water in ethanol. After hydrolysis, continuousglass fiber bundles were dipped into the solution and keptfor 1 h to allow formation of silanol bonds with continuousstirring, then, the solution was removed and glass fiberswere washed with water and then with ethanol to remove thephysisorbed coupling agents. The fibers were then dried inan oven for 10 min at 110  8 C. To check the amount of coupling agent bonded to the fiber surface, a small sample of fiber was analyzed by using TGA (thermo gravimetricanalyzer). This measurement indicated that the weightfraction of coupling agent on the surface was around 0.5%.Contact angles were measured tensiometrically using anelectronic microbalance (Sartorious Microbalance, M25D)equipped with a motor-driven stage that has verticaldisplacement capability of 10 mm. The digital signalsfrom the microbalance were recorded. In the case of glassfibers, a single fiber specimen was prepared first, by tapping1 cm of a 2 cm length of fiber between two pieces of adhesive tape, with about 1 cm of the fiber exposed. The G. Ozkoc et al. / Polymer 45 (2004) 8957–8966   8959  specimen was then placed to the hook of the microbalance.In all experiments a stage velocity of 1  m m/s was used tobring the fiber into contact with the liquid. The force ( F  )measured by the microbalance was then recorded tocalculate the advancing contact angle ( q ) by Eq. (8), F  Z ð P Þð g Þð cos  q Þ  (8)where  P  is the perimeter of the sample and  g  is the surfacetension of the probe liquid. Each contact angle measurementwas repeated at least three times. The contact angle wascalculated from the averages of the measurements. Aftereach measurement to specify the perimeter of sample,0.5 cm of the fiber tip was cut; the remainder was thenbrought into contact with  n -decane, a completely wettingliquid.It is assumed that  n -decane makes zero angle with thesample. Properties of these probe liquids are given in Table2 [21]. Diiodomethane (DIM) was used as the probe liquidfor Liftshitz-van der Waals interactions. Ethyleneglycol(EG) and formamide (FA) were used to identify the acid–base interactions between sample and the probe liquid.For the polymeric samples, the same procedure wasrepeated with a tiny, very thin strip-shaped sample withdimensions of 2 ! 20 ! 0.2 mm. The samples were preparedwith a hot-press at 230  8 C and 100 bars.ILSS was determined according to ASTM D 2344 [22]using the short beam flexural test. Bundles of glass fiberstreated with different silane coupling agents were embeddedinto the polymer matrix using a hot-press, which isillustrated in Fig. 2. The short beams including uni-directional parallel glass fibers at the central position werethen cut from the sheets obtained and tested by using aLloyd 30 K Universal Testing Machine. The support span todepth ratio used was 5:1 with a corresponding specimenlength to depth of 7:1, and crosshead speed was 2.0 mm/ min. The force versus displacement curve for each samplewas recorded.Before blending, ABS and PA6 pellets were dried in avacuum oven at 80  8 C for 4 and 12 h, respectively. The 10,20 and 30 wt% PA6 containing ABS/PA6 batches wereprocessed in a co-rotating twin-screw extruder (Thermo-prism TSE 16 TC,  L   /   D Z 24) at a screw speed of 200 rpmand barrel temperature profile of 195–230–230–235–240  8 C. The extrudate was water cooled and chopped intosmall pellets. The produced ABS/PA6 pellets were againvacuum dried again at 80  8 C for 12 h. The 30 wt% glassfiber reinforced ABS/PA6 composites were prepared byextrusion at the same operating conditions applied pre-viously in the ABS/PA6 blending. The extrudate was againwater cooled and chopped into small pellets. The specimensfor mechanical characterization experiments were moldedby using a laboratory scale plunger type injection-moldingmachine (Microinjector, Daca Instruments) at a barreltemperature of 230  8 C and mold temperature of 80  8 C.All mechanical tests were carried out at room tempera-ture. At least five samples were tested and average resultswith standard deviations were reported for each type of composite. Tensile tests were performed on dog-bonespecimens according to ASTM D638 by using a Lloyd30 K Universal Testing Machine. Charpy impact tests wereperformed by using a Pendulum Impact Tester of CoesfeldMaterial Test, according to the ASTM D256 on rectangularspecimens (6 ! 60 ! 2 mm).Melt flow index values were measured by using anextrusion plastometer (Omega Lab. Ins. Lmt.) according toASTM D 1238 with 5 kg load and at 230  8 C.A low voltage SEM (JEOL JSM-6400) was used toanalyze the tensile fractured surfaces of the composites. Thespecimens were coated with gold to eliminate arcing of thebeam. To obtain the fiber length distributions afterprocessing, approximately 5 g of random samples fromextruded pellets were placed in an oven at 600  8 C for 30 minto remove the polymeric matrix. The remaining glass fibers Table 1Information on materials used in this studyMaterial Trade name Manufacturer DescriptionABS Tairilac w Formosa, Taiwan Extrusion grade Sp. gravity: 1.04PA6 Domamid 27 w Domo, Germany Textile yarn extrusion grade amino-end groups: 44 G 5 meq/kg, Sp. gravity: 1.14Continuous glass fibers WR 3-1200 w Cam Elyaf, Turkey Diameter: 16.0  m m, coupling agent: blend of styrylsilaneand methacrylosilaneShort glass fibers PA-1 w Cam Elyaf, Turkey Diameter: 13.0  m m, coupling agent: aminosilaneTable 2Surface tension components of probe liquids, (mN/m)Surface tension (mN/m) DIM EG FA  n -Decane g TOTL  50.8 58 48 23.83 g LWL  50.8 39 29 23.83 g ABL  – 19 19 – g K L  – 29 39.6 – g C L  – 2.3 2.3 – G. Ozkoc et al. / Polymer 45 (2004) 8957–8966  8960
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