Additives as Impurities

8/4/2019 Additives as Impurities

1/12

Iranian Pulym r Jow,,al Volume 5 Number 1 (1996) 1017- 6020196

The Influence of Impurity Particles on the Mechanical Propertiesof Unreinforced and Short Fibre Reinforced

Thermoplastic MouldingsAli Zadhoush' and Michael J . Bevis

Wolfson Center for M aterials Proc essing, Brunel U niversity, Uxbridge, M iddlesex, U .K .Received : Z 9 Augiat 1995; accepted 24 December 1 9 9 5

A B S T R A C TWhatever may be the reason for the presence of impurity particles, they arelikely to have som e influence on the mecha nical properties and it Is not safeto assume that the data obtained on samples of the particle-free materialcan be used for design purposes The type and amount of added particles,the shape an d size of particles are also important in determining the failurebehaviour . Based on the mechanical testing results and fractographicevidence presented in this work, several observations and conclusionsabout the influence of impurity particles on short and long term mechanicalproperties in short fibre reinforced thermoplastics may be noted.

Unreinforced materials are more prone to failure due to impurity parti-cles than short fibre reinforced plastics (due to the mechanism of thereinforcement of fibres)

Key Words : impu rity particles, injection m oulding, mech anica l properties, short fibre reinforced plastic mou ldings

INTRODUCTIONInjection mou lded parts may contain impurity par-ticles arising from the follow ing sources:polymer feedstock as gel particles and poly-merization additives. co mpo und add itives as oversize particles andagg lom erates, pigm ents, stabilizers, fillers, etc. material handling as paper fibres, metal frag-ments from materials handling equipment.processing m achinery as d etached metal partsfrom wo rn machinery, d egraded polymer from pro-

cessing d ead spots.Impurity particles arising from the last two

sources are likely to arise in feedstock preparedfrom reground plastics.

The results of several literature searchesduring the course of work has failed to provideinformation covering the cau ses and types of impu -rity particles, and their influence on mechanicalproperties for sho rt fibre reinforced thermoplasticsmoulding . How ever, few researchers have carriedou t some wo rk on unreinforced materials . Studiescarried out by Sandilands et al. [1], have been

' Prrscnt Address : Textile Department, Isfahan tlnivet'sity of Technology, Isfahan, LR-Iran

4


2/12

The Influence o[ Impurity Particles on the Mechanical Properties

involved with the stress rupture lifetime of poly-ethylene pipes, which have been seen to fail in abrittle manner with fracture initiating from someinhomogeneity within the pipe wall, such as ametal particle . Such failure is associated w ith slowcrack growth . It was concluded that the stressruptu re lifetimes of po lyeth ylene pipes failing in abrittle manner, depended upon the size of theadventitious flaw which initiated fracture . Thework carried out by the author [2] has shown thatcontamination reduced the ductility of the plasticwith the contaminated specimens tending to bemo re brittle than the virgin specimens.M atushige et aL[3] have carried o ut w ork onthe origin of parabolic markings on PM M A fract-ure surface . They have concluded that as staticfactors there exist several kinds of defec ts such asforeign materials and inhomo geneities inside o f thepolym er upon the c rack propagation, strong stresswaves are emitted in advance to a primary fractu refront as dynamic factor, and cau se loc ally a highlystress- concentrated region selectively at thesedefec ts, activating finally the seco ndary f racture.

In Haskell et al.14] work on effects of flowon orientation of carbon short fibre reinforcedpolyc arbonate, an interesting f inding o f the reportwas the appearance o f a co ntaminant in the speci-men. A g lass fibre is believed to be the po int wherefailure began . They co nclud ed that contaminationof the poly mer may have harmful effects and careshould be taken to prevent it.

Po wd ers may he added to f ibrous compo sitesas cost-reducing fillers, as pigments or as nuclea-ting agents for rapid processing . They may beintended to alter the mechanical properties, toreduce the thermal expansion or to improve the

165

13

57

Figure 1 . Specimen dimensions of D638 type bar in mm .

processability and surface finish . Some particlesmay be present in the received materials, in theform of contaminant particles for agglomerationsof an insolu ble add itive.The type and amo unt of ad ded particles , theshape and size of the particles, are also importantin determining the failure behaviour [1].

EXPERIMENTALIn order to investigate the effects of added parti-cles on m echanical properties, aluminium particleswere deliberately ad ded to the m ou lding materials,using a small quantity o f oil as adhesive agent andmixing was carried out by hand before transfer tothe injection mo uld er hopper . The follow ing parti-cle size ranges were used to observe their influenceon the m echanical properties:

116150180250,u250300 fe300425 u425850 ,u

Particle size range of 106150 ,u was usedfor carbon and glass fibre reinforced polyether-etherketone (PEEK) and the others were used forunreinforced and glass reinforced polypropylene.To show the effects of amount of added particleson the mechanical properties, four differentformulations of polymer and aluminium particleswere chosen with the following com positions: virgin material

0.05 w/w aluminium particles 0.1 w/w n-- 0.2 w/w

Standard tensile test bars and 6 X 6 mmdu mb-bell shaped bars were mou lded, The d imen-sions of the specimen cavities are shown in Figu res1 and 2.

The Figures 3 and 4 are photographs prod-uced from radiographs of selected samples, andillustrate the presence of aluminium particles inthe mouldings.

A series of mouldings were produced foreach formulation, and before the production of

1 9

3

5 Iranian Polymer Journal Volwne 5 Number I (1996)


3/12

2adhoush A rt al.

6

Figure 2 . Specim en dimensions of the b ar used for tensileand flexural fatigue testing in m m.mou ldings at each stage, the fol lowing procedu reswere carried out to avoid contamination from theprevious f ormu lation:

I- Removal of all arising polymer from thehopper and then empty the barrel.2- U ncontaminated virgin polym er is introd uc ed

to purge and abou t 10 mou ldings produced.3- Stage (1) is repeated and then polymer withnew formulation is introduced and mouldingcontinued.The first ten mou ldings in each run were dis-carded to ensure machine-equilihrium conditionshad been attained . The sprue and runners on eachspecimen were removed and the specimensnumbered_MaterialsNatural and GFR PPNatural polypropylene (GXM43) .20% g lass fibrereinforced (HW60 GR20) and 30% glass fibrereinforced (HW60 GR30) polypropylene weresupplied by Imperial Chemical Industries (ICI) ingranular form.

Polypropylene (PP ) belongs to the polyo lefinclass of polymers and is polymerizing propylene((CH 2 -CH(CH 3 )1), its density is among thelowest of all plastics . Properties of the polymervary widely according to molecular weight andmethod of preparation . The grades used for

a b C d e

Figure 3 . Photograph s produced from radiographs of 3mm moulded bars made from 3 0% G FR polypropylene, (a)particle-free and containing 0 .2 wlw alum inium pa rticles ofsize range (b) 180250 u (c) 250-300,U (d) 300425 11(e) 425850 t .mo uld ing plastics have molecular weight of 40,000or mo re , they are usually highly crystal l ine, havegood resistance to heat and chemicals, and goodelectrical properties . PP can be modified to gainimproved properties by incorporation of short glass

1 2 .5

Iranian Polymer JoaLmal Volume S .Number 1 (1996) 6


4/12

The Influence of im purity Particle; on the M echanical Properties

Figure 4 . Radiograph photographs of 6 mm moulded barmade from 30% GFR polypropylene, conta in ing 0 .2 wlwaluminium particles of size range 350 425 /4.fibres into t he mat rix . The physical properties arerepresented in Table 1 [5].30% CFR and 30% GFR PEEKPEEK is a linear aromatic polymer which can bechemically described as a poly(arylether ketone)based on the fallow ing repeat unit:Table 1 . The ph ysical properties of natural and G FR PP.

Properties Natural 20 %GFR '

30%GFR '

Melt flow index at 23 0 ' Cand 2 .16 kg, g110min 9 .0 4 .0 3.0Density (mean), gem - 3 0.905 1 .04 1 .12Tensile yield stress, MPa 34 .5 72.4 86.2Flexural modulus, GPaIzad Impact strength

1 .72 4 .9 6 6.5at 23 'C, JlmMoulding shrinkage at

40 70 10020 'C, % 1-2 0 .2-1 .0 0 .2-1 .0

"These materials are anisotropic and therefore the values given depend onthe orientation of the glass fibres in the m oulding .

The combination of a high continuous ser-vice temperature of 260 'C, excellent wear,abrasion, and fatigue resistance, outstandingmechanical properties and excellent chemicalresistance make PEEK an ideal material for anextremely w ide range of applications.

Glass and carbon fibre reinforced P E E Koffer all the properties associated with theunreinforced material and also greatly improvedmec hanical properties, heat distortion temperatureand w ear behaviour.

The 30% glass fibre (450 0L30) and 30%carbon fibre (450 CA30) reinforced P E E K wereused, supplied from ICI (Table 2) [6].Sam ple PreparationMoulding 3 mm Tensile Bar (30% GFR and 30%CFR PEEK)The reciprocating injection moulder used in thispart of the work was a Sandretto 6GV(50 tonnemode l . Although the machine could he manuallyoperated, but it had a fully automated micro-Tab le 2 . The physical properties of natural and reinforcedPEEK.

Properties N atural 30%G FR

30%CFR

Density, gcm - 3Typical level of

1 .3 2 1 .4 9 1 .44crystallinity, % 35 35 35Mould shrinkage, %Flexural modulus at

1 .1 0.5 0 . 1 1 .4'23 .C, GPaFlexural strength at

3 .66 10 .3 1 1 3 .023 'C, MPaTensile strength at

170 * 23 3 318 .23 'C, MPa 92Y 157h 208 bElongation at break, % 50 2.2 1 .3

'Yield value al >5% strain are esbmared values.Anisotropic, 6: Break . y! Yield.

7 Iranian Polymer Journal Volume 5 Number I ( 1996)


5/12

Zadhow& A et e l .

processor control accessory.A d ou ble cavity single gated standard tensiletest bar (ASTM D 638 type 2) mou ld was used for

the production of test specimens . The test mater-ials were d ried in a vacuu m o ven overnight at 150' C . In order to investigate the effects of addedparticles on mechanical properties, the followingco mpositions were cho sen: virgin polym er adding 0 .2w/w aluminium powders (doublysieved) w ith a 106150 u particle size range.

A Dynisco FT 44 4 1000 psi (6 .89 X 106 N lm 2 ) ,strain gauge transducer was located behind adummy ejector pin, and the changes in cavitypressure during mould filling were continuouslymonitored to ensure good reproducibility andoptimum mould filling. Suitable processing para-meters were carefully c hosen.Moulding 3 mm Tensile Bar (20% GFR and 30%GFR PP)The reciprocating injection moulder used for thispart of work was a Negri Bossi (NB85-240-85).The machine co uld be manu ally operated, bu t hada fully automated microprocessor control access-o ry . Procedure above was repeated using thefollowing fo rmulation:

virgin polymer, 20% GFR and 30% GFRpolypropylene. add ing alum inium pow der in three concentr-ations of 0 .05w/w, 0.1w/w and 0 .2w/w,

This part was repeated for aluminium pow-ders (do ubly sieved) having the fo l lowing particlesize ranges : 180250 y

250300 Ft300425 le425850 EeSimilar procedure was used for producing 6mm bars.

RESULTS AND DISCUSSIONTensile tests were carried out on the completerange of mo uld ings . Restrictions, du e to geom etryof some mouldings, cost and time resulted in the

limitation of impact and fatigue tests to selectedspecimens.The results of mec hanical tests are presented

in tables, accompanied by a statement of testingconditions . In order to encourage brittle failure ahigh crosshead speed of 500 mm /min was used.Un reinforced and G lass Fibre Reinforced Poly-propylene20% GFR PPThe results for specimens containing includedalum inium particles with d ifferent size-ranges andin different co ncentrations are presented in Tables3 and 4 .

Table 5 presents Charpy impact test resultsgained from 3 mm bars containing aluminiumparticles.Examination of the tensile modulus (E),tensile stress (u) and strain to failure (%e) datafrom tensile tests, failure energy (FE ) and failuredeflection (Fn) from impact tests, show that thereis no significant dependence on the presence ofaluminium particles.The tensile strengths obtained are similar tothe strength data provided by the materials supp-lier (ICI).30% GFR PP (Tensile Test Bar of 3 mm thick-ness)Using two crosshead speeds of 200 and 500mm /min tensile test results gained are presented inTables 6 and 7. The full range of particle-free andbars containing aluminium particles were used inthe tests.

The tensile strength o btained are identical tothe tensile strength d ata provided by the manuf ac-turer (ICI) . Figures 5 and 6 are scanning electronmicrographs of typical tensile fracture surfaces.Comparison of these fracture surfaces indicatesthere are no readily apparent differences in frac-ture surface morpho logy which can be attributed tothe presence of alum inium particles.30% GFR PP (Tensile Test Bar of 6 mm thick-ness)The results of tensile tests of representativespecimens are presented in Table 8 . Fatigue testresults for the same range o f specimens are shown

Iranian Polymer Journal Volume 5 Number 1 (1996) 8


6/12

The Influence of I m p u n r y Fanjet. on the Medianical Properties

Table 3 . Tensi le test results for 20% GF R p olypropylene ASTM tensi le bars of 3 m m thickness, free from and con tainingalum inium particles [crosshead speed : 200 mm /min , Gauge length : 100 mm , Temperature : 23 `C).

Particle-freeAdded part icles

0 .05 w/w 0 .1 w/w 02 wlwParameters

a E E !T_

t : E t7 E t7 E E(MPa) (%) (GPa) (MPa) (%) (G Pa) (MPa) (%) (GPa] (MPa) (% ) (G Pa)

Mean * 70 .6 4 .1 2.6 7 1 .1 4 .1 2.5 7 1 .7 4.1 2 .5 70 .7 4 .0 2 .6SD' 0 .402 0.045 0 .130 0.408 0 .158 0 .141 0 .334 0 .230 0.151 2 .118 0.241 0 .130Mean s 70.6 4 .1 2 .6 59 .6 4.0 2 .6 7 1 .5 4.0 2 .8 71 .6 4 .0 2 .7S D* 0 .402 0.045 0 .130 1 .868 0 .164 0.217 0.200 0 .179 0.148 0 .559 0 .219 0 .100Mean 70.6 4.1 2 .6 7 2 .0 3.9 2 .9 720 3.9 2 .8 71 .5 3.9 2 .8SD`' 0 .402 0 .045 0 .130 0 .505 0 .158 0 .100 0.505 0 .148 0.130 0 .219 0 .071 0 .109Mean + 7 0 .6 4 .1 2 .6 70 .7 3 .7 3 .1 7 1 .4 3 .9 2 .7 7 1 .0 3 .8 2 .8SD + 0 .402 0 .045 0 .130 0 .297 0 .264 0 .400 0.962 0.084 0 .100 0 .720 0 .152 0 .109

NB ; Five tests per quoted resatSD ; Standard deviation.Size range : . 180-250 , 0 250-300 p, i. 300-425 0 . + 425-850 p.

Tab le 4 . Tensi le test results for 20% G FR p olypropylene ASTM tensi le bars of 3 mm thickness, free from and con tainingalum inium particles (Crosshead speed : 500 mm lmin, Gauge length : 110 m m, T emperature : 2 3 ' C).

Particle-freeAdded particles

0.05 w!w 0 .1 why 0 .2 w/wParametersa E E 6 E E 1 5 E E U E E

(MPa) (%) (G Pa) (MPa) (%) (GPa) (MPa) ( % ) (GPa) (MPa) (% ) (GPa)

Mean 72 .7 3 .4 2 .8 73.1 3 .5 2 .7 7 2 .3 3 .5 2.6 70 .0 3 .2 2.6SD . 2.427 0 .148 0.083 0 .913 0.055 0 .109 1 .080 0 .109 0 .045 2.442 0 .151 0 .071Mean' 72 .7 3.4 2 .8 7 1 .6 3 .6 2.5 7 1 .7 3 .7 2.5 72.8 3 .6 2.5SD 2.427 0 .148 0.083 0 .693 0.158 0 .083 1 .259 0 .164 0 .044 0 .862 0 .187 0 .083Mean 72 .7 3 .4 2 .8 72 .6 3.8 2 .5 7 1 .7 3.6 2 .5 7 1 .4 3.4 2 .6SD" 2.427 0.148 0 .083 0 .493 0 .148 0.114 2 .797 0 .249 0.045 1 .194 0 .045 0.089Mean ' 72 .7 3 .4 2 .8 70 .6 3.5 2 .5 7 1 .5 3 .5 2.5 7 1 .6 3 .4 2.5SD* 2 .427 0 .148 0 .083 2 .210 0 .192 0.071 2 .180 0.151 0 .083 1 .436 0.100 0 .089

NBi Five tests per quoted resultS D' . Standard deviation.Size range: . 180-250 1a . 250- 00 Ir . C 300-425 p, + 425-850p.

9 Iranian Polymer Journal Volume 5 Number I f1996)


7/12

Zedhoedi A of al.

Tab le 5 . Impa ct test results for 20% G FR polypropylene tensile bars of 3 mm thickness free from an d containing 0 .2 wlwaluminium particles (F E = Failure energy in Nm an d F0= Failure deflection in mm).

Added particlesParameters Particle-free

180-250,u 250-300 U 300-425yMeanSD

0 .9940 .084

6 .600 .210

1 .0750 .075

6 .880 .202

1 .0650 .074

7.060.221

1 .0500 .031

7.380.238

N B; Fire taste per quoted resultVelocity ; 2 msWeigh ; 27 kg

in Table 9 . Only one specimen for each formul-ation was tested , using six stress levels.Within the experimental errors the tensiletest results do not reveal any sintificant reduction

in properties due to the presence of the addedparticles.However, the tensile strengths of all speci-

mens were 25% below t he strength values specifiedby the materials supplier. Fatigue test results b asedon one specimen of each type fail to show any

consistent reduction in endurance due to thepresence of add ed-particles.Natural PolypropyleneTable 10 p resents the tensile test results u sing 200and 500 mmlmin crosshead speeds . The Charpyimpact test results are shown in Table 11.

All of the specimens containing included-particles which were tested at 200 mm lmin failed ina brittle manner and all of the virgin specimens

Tab le 8 . Tensi le test results for 30% G FR p olypropylene ASTM tensi le bars of 3m m th ickness, free from an d containingaluminium partic les (Crosshead speed : 200 m m lmin, G auge length' 100 m m, T emperature : 2 3 c C) .

Added particlesParticle-tree

0 .05 wlw 0 .1 wive 0 .2 wlwParametersa

(MPa)e

(%)E

(GPa)v

(MPa)e E U

(MPa)E

(%)E

(GPa)a

(MPa)E

(% )E

(GPa)%) (GPa)Mean ` 8 5 .3 3 .7 3 .6 79 .5 3.5 3 .2 8 1 .5 3.8 3 .2 8 1 .0 3 .9 3 .2SD' 1 .053 0.083 0 .181 2 .335 0 .055 0.219 0.784 0 .109 0.130 0.313 0 .045 0 .164Mean' 8 5 .3 3.7 3 .6 79 .3 3.8 3 .1 8 1 .0 3 .8 3 .4 77 .1 3 .8 3.0SD' 1 .053 0.083 0 .181 0 .743 0 .071 0.100 0 .522 0 .114 0.217 0.761 0.084 0 .217Mean' 8 5 .3 3.7 3 .6 8 1 .4 3.8 3 .1 80 .2 4 .0 3.2 79 .5 3 .9 3.2SD" 1 .053 0.083 0 .181 0 .672 0 .114 0.219 1 .499 0 .084 0 .084 1 .631 0.114 0 .084Mean' 85 .3 3.7 3 .6 7 8 .6 3 .7 3.2 7 9 .2 3 .9 3.2 79 .1 3 .6 3.2SD + 1 .053 0 .083 0.181 2 .442 0 .192 0.114 0 .479 0.084 0 .100 1 .492 0.321 0 .130

N B : Five tests pet quoled resultSO : Standard deviation.Side ran5 .e : 180-259 pt . n 250-30014 . 0 300-425 p . + 425-8501x.

Iranian Palmer Journal Vdonm 5 Number 1 [19961 10


8/12

TLe rufluence of Impurity Particles on the Mechanical Properties

Tab le 7 . Tensi le test results for 30% GFR polypropylene of 3 mm AST M tensile bars, free from an d containing alum iniumparticles (Crosshead speed : 500 mm lmin, Gauge length : 110 mm, Temperature : 23 'C) .

ParametersParticle-free

Added particles

0.05 w/w 0.1 w/w 0.2 w/wU

(MPa)t :

(%)E

(GPa)a

(MPa)s E a E E U

(MPa)r

(%)E

(GPa)% ) (GPa) (MPa) (% ) (GPa)Mean' 85 .6 3.1 3 .56 8 6 .2 3.2 3 .3 8 5 .6 3 .2 3 .2 85 .3 3 .3 3.1SD ` 1 .106 0.071 0 .089 0 .455 0 .114 0.130 0 .559 0 .045 0.158 0.559 0.151 0 .089Mean. 85 .6 3.1 3 .6 8 4 .9 3 .4 3 .0 8 4 .1 3 .3 3.1 85 .0 3 .4 3.0SD S 1 .106 0 . 0 7 1 0.089 1 .165 0 .122 0.084 1 .561 0 .130 0 .249 0.999 0.122 0 .084Mean- 85 .6 3.1 3 .6 8 5 .7 3 .4 3.1 8 5 .3 3 .3 3.1 84.6 3 .3 3.0S0 1 .106 0 . 0 7 1 0.089 0 .829 0 .179 0.089 0 .756 0 .122 0 .109 1 .984 0.179 0 .089Mean * 85 .6 3.1 3 .6 8 4 .0 3 .3 3.0 8 3 .5 3 .3 3.0 84 .4 3 .2 3.1Sp * 1 .106 0 . 0 7 1 0.089] 2 .631 0 .192 0.114 2 .291 0 .100 0 .045 1 .474 0.134 0 .130

Na . Five tests par quoted resultSD ; Standard deviation.Size range! * 180-250 Fr, 0 250-300 it, c. 300-425n, -F 425-850 F e .

failed in a duc tile manner.This demonstrates that the presence ofaluminium particles has reduc ed the du ctility of the

material and is reelected in a sharp decrease ofabou t 44 % in s train to fai lure.However the tensile strength and modulus

Figure 5 . Scanning electron micrographs of fracturesurface of 30% GPR polypropylene AST M test bars (1 /2cross section of the bar) .

were not influenced by the presence of aluminiumparticles . The effect of embrittlement associatedwith the presence of aluminium particles was lesspronounced at the 500 mm/min crosshead speedtests .

The scanning electron microscopy observ-ations combined with elemental analysis showedthat aluminium particles initiated failure in thepolypropylene containing aluminium . Some typicalexam ples are show n in Figure 7 . The fracture sur-face of the included-particles specimen shown in(b) ex hibits a typical fast crack grow th region.

The results gained from the impact testingreflect the results gained by tensile testing . Themeasured failure energy and deflection decreasewhen aluminium partic les arc ad ded .30% CFR and 30% GF R Polyetheretherketone30% CFR PEEKTable 12 presents tensile test results for test barspecimens of 3mm thickness.

Within the experimental errors, the tensiletest results combined with scanning electron

II Iranian Pulyvner Journal Vniu+nc 5 Number 1 (1996)


9/12

Zadhoueh A et al.

(a)

(b)Figure B . Scanning electron micrographs of fracturesurfaces of 30% GFR polypropylene AST M tensile test barcontaining 0 .2 wlw aluminium p articles . (a) Typical fracturesurface of 11 2 cross section of the bar, (b) Detail showin gthe presence of an alum inium particle.microscopy observations reveal no significantdifferences in the trends of tensile properties forparticle-free and mouldings containing included-particles.

In order to gain some understanding offatigue behaviour of the specimens, some limitedcxperimental .tests were caned out at various

Table 8, Th e results for tensi le test for 6 mm tensi le bar(dumb-bell) made from 30% GFR PP, particle-free andcontaining 0 .2 wlw a luminium part ic les wi th s ize range300-425,u (Crosshead speed 2 mm lmin, Gaug e length:50 m m, T emperature : 23 ` C J .

Sample Particle-free Added-particlesa E 1 E a F. E

(MPa) (%) (GPa) (MPa) (%) (GPa)1 64 .0 4 .7 3.4 6 1 .8 5 .8 2.72 62 .0 4 .2 3.3 65 .4 5 .10 3.63 63 .4 4 .6 3.1 62 .8 3 .8 3.54 63 .0 4 .2 3.5 63 .2 4 .2 3.05 65 .7 4 .3 3.3 64 .8 5 .0 3.2Average 64 .0 4 .4 3.3 63 .6 4 .8 3.2

temperatures and stress levels. These results arcgiven in Table 13.There is an evidence in Table 13 that the

influence o f alum inium particles on the long termproperties is much more significant than the shortterm properties . Thus there appears to be asubstantial reduction {60%) in the number ofcyc les to failure du e to the presence o f aluminiumparticles.30% GFR PE E KThe tensile test results fo r particle-free and m ou ld-ings co ntaining alu minium particles are presentedin Table 12.

The results follow the same trends as forTab le 9 . Th e fatigue test results for fatigu e test based onone specimen for 6mm bar (dumb-be l l ) made from 30%GF R PP, part icle- free and con taining 0 .2 wlw aluminiumparticles (Environment: air, Temp erature: 2 3 Frequency:1 Hz, M ode tension/com pression, Waveform : square).

Endurance (cycles)Stress (MPa) '-

Particle-free Added-particles3 6 47 5 2,2003 4 45 0 1,55032 2,200 1,55030 4,250 13,50028 25,000 105,00026 650,000 150,000

Iranian Polymer Journal Volume .5 Number 1 (1996} 12


10/12

The Influence of Impurity Panicles on the Mechanical Properties

Table 10. Ten sile test results at 23 'C for AST M natura l polypropylene tens i le bars of 3 m m th ickness, f ree f rom andcontaining 0 .2 wlw aluminium part icles.

Size rangePara-

Particle-free180250 1 u 250300,u 300425 it 425850 F s

metersU E E U

(MPa)E

(%)E

(GPa)U

(MPa)E

(%)E

(GPs}U

(MPa)E

(% )E

(GPa)U

(MPs}E

(%)E

(GPa)MPa) (%) (GPa)Mean 3 6 .5 27 1 .3 3 6 .7 1 6 1 .5 36 .6 1 7 1,4 36 .5 1 5 1 .4 36.2 15 1 .4SD S ` 0 .109 2 .949 0.109 0 .223 0.447 0 .109 0.148 0 .707 0.200 0 .616 0 .447 0 .089 0 .917 1 .140 0 .109Mean 3 7 .7 1 8 1 .2 3 7 .6 1 4 1 .1 36 .7 1 4 1 .0 37 .7 1 3 1 .0 37.4 14 1 .0SO 0 .00 1 .140 0.071 0 .296 1 .341 0.100 0 . 9 6 1 0 .548 0 .187 0 .316 0.836 0 .148 0 .311 0.837 0 .045

Ne : F ive tests per quoted result.S D ; S tandard deviation. C rosshead speed : 200 mm/min, Gauge length : 100mm. Crosshead speed : 500 mmlmin Gauge length: 110 mm.

30% CFR PEEK, and reflect no notable differ-ences due to the presence of the aluminiumparticles.

The tensile strengths obtained are similar tothe value of 157 MPa referred to by the manufac-turer.

CONCLUSIONThe tensile and impact test results and fracturemechanisms, as interpreted by scanning electron

microscopical fractography reported in this workfor 3 mm bars made of 20% GFR PP, 30% GFRPP, 30% GFR PEEK and 30% CFR P E E K ,indicate there are no readily apparent differencesin mechanical properties or fracture surfacemorphology which can be attributed to thepresence of aluminium particles . The tensilestrengths obtained for particle-free test bars andbars co ntaining alum inium particles are identical tothe tensile s trength d ata provided by the manufac -turers . The amount and type of fibre as well asdifferent crosshead speeds used for the samples

Table 1 1 . Impa ct test (Cha rpy) results for 3 mm natu ral polypropylene bars, free from and con taining added alum iniumparticles 2 .2 wlw (Velocity : 2 ma', Weight: 27 kg, Span : 50 mm , Temperature 23 'C).

Particle-treeSize range

180250[ 250300 U 300425,uFailureenergy(Nm)

Failuredeflection

(mm)Type

offailure

Failureenergy(Nm)

Failuredeflection

(mm)Type

offailure

Failureenergy(Nm)

Failuredeflection

(mm)Type

offailure

Failureenergy(Nm)

Failuredeflection

(mm)Type.af

failure3 .18 31 .7 ductile 2 .24 1 7 .9 brittle 1 .9 7 16 .3 brittle 2.04 1 7 .0 brittle

NB : F ailure mode was selected by the computer program based on force-deflection records.

13 Iranian Palynner Journal Volume 5 Murtha I (1996)


11/12

Zadhottsb A. et at.

( a ) ( c ]

(b) (d )Figure 7. Scanning electron micrographs of fracture surfaces of natural polypropylene tensile tested specimens . (a)aluminiumfracture initiating particles, (b) Fractured cross-section of the bar containing 0.2 wlw aluminium particles showing brittlefracture . (c) similar as (a), (d) fractured cross-section of a bar free from aluminium particles showing ductile fracture.

investigated d id not make any significant chang es.Within the aluminium particle size rangeinvestigated , a larger num ber of sm all particles isnot more effective than a small number of largeparticles in influencing the mechanical properties.

How ever, the results gained fo r unreinforcedPP show that all of the specimens containinginclud ed-particles failed in a brittle manner and allof the virgin specimens failed in a du ctile manner.

This demonstrates that the presence of alu-

minium particles has reduced the ductility of thematerial, and is reflected in sharp decrease ofabout 44% in strain to failure. However, thetensi le s trength and mod ulus are not influenced bythe presence of aluminium particles_

The presence of aluminium particles appearto have significant degrading effec t on the fatigueproperties of 30% CFR PEE K bars . This demo nst-rates that long term mechanical properties arestrongly influenced by the add ed particles.

lroniari Polymer Jnumai Volume .5 Number 7 (1996) r4


12/12

The Influence at Impurity Particles o the Mechanical Properties

Table 12. The 30% GFR PE EK and 30% CFR PEEK tens iletest results for 3 m m AS TM tensile bar, particle-free, and0 .2 wlw added aluminiu m p art icles (Crosshead speed : 2ram/Min , Gauge length ' 110 mm , Temperature : 2 3 'C).

Particle-free Added-particlesSample O

(MPa)E

(%)E

(GPa)U

(MPa)E

(%)E

(GPa)3 0 % C F R 213 .5 3 .2 7 .5 204 .3 2.8 7.6

PEEK3 0 % G F R 142.4 2 .8 4.9 149 .3 3.0 5 .0

PEEKSimilar observations were gained for 6 mm

(dumb-bell) bar mouldings . How ever, the tensilestrength of all the specimens were 20% below thestrength values specified by the materials supplier.This is due to the anisotropic nature of thesematerials, the strength valu es specified b y the m at-erials supplier is based o n 3 mm bars . Fatigu e testresults based on one specimen of each type failedto show any co nsistent reduction in endu rance d ueto the presence of alu minium particles.Presence o f ad ded particles were not cri t icalin determining tensile properties of short fibrereinforced thermoplastics . This supports the co n-Table 13 . Fat igue test resul ts for 30% CFR PEE K 3 m mtensile bars for particle-free, and containing 0 .2 wlwaluminium powder with size range 106150y (Environ-ment: air, Frequency : 5 Hz, Cyc lic stress: 7575 MNlm 2 ,Mean stress : 75 MN/m 2 , Temperature : 23 ' C, Mode'repeated tensile, Waveform: sinusoidal) .

Endurance (cycles)Sample

Particle-free Add ed-particle 0 .2 wlw1 36,000 14,5232 44,34-4 15,2003 47,912 18 ,0584 53,940 22,1805 55,900 27,100

Ave 47,620 19,411

tention that strength in these materials is predom-inantly orientation- controlled .

Fatigue results indicate that fatigue loadinghas a more damaging effect on the interface andthat cyclic d amage starts as loc alized d ebond ing.

REFERENCES

1. Sandilands G., Kalman P., Bowman J. and Bevis M . J .,Polymer Commwtkation, 24, 273275, 1983.

2. 2adhoush A., T he Filtration of Filled Thermoplasticduring lnjeclion Moulding, M .Sc . dissertation, BrunelU niversity, September 1983.

3. Matushige K ., SakuradaY . and-Takahashi K ., Reports onProgress in Polymer Physics in Japan, Tokyo, 25, 353356,1981

4. Haskell W ., Petrie S. and Lewis K. Plastics "MeetingChallenges of the Future", Exhibition, San Francisco,California, 292294, May 1013, 1982.

5. ICI Propathene (Polypropylene), Technical Service Note,PP 34 .

6. Technical Service Note VK2, ICI Victrex (P E E K ).

I5 Iranian Poly mer Journal Volume 5 Number I (1A9 )

Additives as Impurities

Documents

Transcript of Additives as Impurities