research article orientation mapping of extruded polymeric...

Research ArticleOrientation Mapping of Extruded Polymeric Composites byPolarized Micro-Raman Spectroscopy

Xiaoyun Chen1 M Anne Leugers1 Tim Kirch2 and Jamie Stanley1

1Analytical Sciences Core RampD The Dow Chemical Company Midland MI 48667 USA2Dow Building Solutions The Dow Chemical Company 200 Larkin 1605 Joseph Drive Midland MI 48674 USA

Correspondence should be addressed to Xiaoyun Chen xchen4dowcom

Received 5 August 2014 Accepted 8 September 2014

Academic Editor Jie-Fang Zhu

Copyright copy 2015 Xiaoyun Chen et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Molecular orientation has a strong influence on polymeric composite materialsrsquo mechanical properties In this paper we describethe use of polarized micro-Raman spectroscopy as a powerful tool to map out the molecular orientation of a uniaxially orientedpolypropylene- (PP-) based composite material Initial samples exhibited a high degree of surface fibrillation upon cutting Ramanspectroscopy was used to characterize the degree of orientation in the skin and guide the development of the posttreatment processto optimize the skin relaxation while maintaining the high degree of orientation in the rest of the board The PP oriented polymercomposite (OPC) was oriented through an extrusion process and its surface was then treated to achieve relaxation Micro-Ramananalysis at the surface region demonstrated the surface orientation relaxation and the results provide an effective way to correlatethe extent of relaxation and process conditions Larger scale orientation mapping was also carried out over the entire cross-section(127 cmtimes 254 cm)The results agreewell with prior expectation of themolecular orientation based on the extrusion and subsequentquenching process The methodologies described here can be readily applied to other polymeric systems

1 Introduction

Polymer composites are gainingmarket share in constructionmarkets and offer several advantages over the traditionalwoodmaterials A variety of plastic compositemanufacturersare offering products for the decking window and door andother specialty markets A recent development is an orientedpolymer composite (OPC) Using a temperature controlledproprietary orientation process products can be fabricatedwith a unique combination of low density high stiffnessgood processability with traditional wood-working toolsand weatherability compared to traditional plastic compositestructures Unlike wood boards where the orientation of thefibrils and microfibrils is aligned by nature to maintain stiff-ness semicrystalline polymeric materials must be orientedduring processing to align the polymer chains to achieve thedesired stiffness

A high degree of orientation of amorphous regions andcrystalline regions is quite desirable formodulus and stiffnessunder load however the orientation can present issues withthe shaping and cutting of the composites to form the final

part Initial products showed a high degree of orientation onthe surface of the product that extended toward the centerof the parts dimensions These products exhibited highlyundesirable fibrillation during surface wear evaluation andcutting Efforts were initiated to understand and improveboth wear and cutting performance

Extensive studies have been previously carried out tocharacterize molecular orientation of a wide range of systemssuch as liquid crystals polymers proteins and peptidesusing vibrational spectroscopic tools For example polarizedinfrared spectroscopy (IR) can be used to obtain orderparameter defined as 119878120579 = (3⟨cos

2120579⟩ minus 1)2 where 120579 is

the angle of the functional grouprsquos dipole moment relative tothe symmetry axis and the bracket denotes ensemble average[1] However the requirement of thin samples sectionsfor transmission mode or a good contact with attenuatedtotal reflectance (ATR) crystals in the ATR mode limitsthe application of IR for molecular orientation study in anindustrial environment Polarized Raman spectroscopy offersmore flexibility as signals can be generated from any surfaceor cross-section in a contact-free fashion and in theory yields

Hindawi Publishing CorporationJournal of SpectroscopyVolume 2015 Article ID 518054 7 pageshttpdxdoiorg1011552015518054

2 Journal of Spectroscopy

more information For example the second and fourth termsof the orientation distribution function characterized byLegendre polynomial ⟨1198752(cos 120579)⟩ and ⟨1198754(cos 120579)⟩ can be cal-culated for vibrational modes whose Raman tensor is known[2 3] Other higher order spectroscopy techniques such assecond harmonic generation (SHG) [4 5] and sum frequencygeneration vibrational spectroscopy (SFG) [6ndash8] have alsobeen shown to provide insights into molecular orientationespecially when combined with linear spectroscopy tech-niques such as IR or Raman Their complex instrumentationand data analysis and surfaceinterface-specific nature havelimited their applications mostly to academic settings

Here we describe an industrial application of polarizedRaman spectroscopy to characterize the molecular orien-tation of polymers within an oriented composite materialwith uniaxial orientation It is demonstrated that through theuse of orientation ratio (OR (1)) the molecular orientationof OPC can be effectively characterized on length scalespanning from 120583m scale to macroscopic scale thus enablingthe mapping of orientation across the entire cross-section ofan OPC sample OR is defined in (1) where 1198681 stands for theintensity of a band that is sensitive to polarization while 1198682stands for the intensity of another band that is insensitive topolarization or shows the opposite trend The 119885119885 and 119884119884 inthe subscript denote whether the spectrum is collected withthe electric field of the excitationcollection beam parallel orperpendicular to the extrusion direction of the sample (seeFigure 1)

OR =11986811198851198851198682119885119885

11986811198841198841198682119884119884

(1)

Although this approach does not yield detailed quantita-tive orientation distribution functions as the more elab-orate polarized Raman methods previously developed itssimplicity and robustness make it suitable for industrialapplications where most samples have many nonpolymercomponents such as additives fillers and pigments VoyiatzisandAndrikopoulos showed that despite the use of calibrationcurve the OR can potentially be correlated to the variousterms of the orientation distribution function [9] Thiswas not necessary for the applications investigated hereinVoyiatzis and Andrikopoulos also demonstrated that forwell-behaved systems such as a dye dissolved in polymericmatrix the orientation of the dyemolecules can be effectivelycharacterized by a simple ratio of 11986811199111199111198682119911119911 which enablesfast monitoring of orientation during a drawing process Theassumptions behind this approachmay not always be satisfiedby many industrial OPC samples For example difference incrystallinity may be another factor that may cause a changein the 11986811199111199111198682119911119911 ratio [10 11] The 11986811199101199101198682119910119910 term in thedenominator of the OR equation can effectively accountfor the variation of other factors such as crystallinity andconcentration

2 Materials and Methods

21 OPC Board Production The details on the OPC extru-sion and processing can be found in previous patents [12]

An appropriate formulation consisting of both miscible andnonmiscible components is extruded into a profile usingstandard material feeding and extruding technology Theextruded profile is then uniaxially drawn using a drawing diein a temperature controlled environment The ratio of theproduct dimensions before and after drawing is known asthe drawing ratio As the drawing ratio is increased towardsits optimum value density tends to decrease while productstiffness defined by flexural modulus and elasticity tends toincrease

Use of high draw ratios tends to produce productswith high degrees of surface orientation While the level oforientation generates many useful properties for the orientedpolymer composite high surface orientation causes issueswhen the productrsquos surface undergoes surface wear or theproduct is cut to specific lengths or shapes As noted earlierthe high degree of orientation tends to generate fibrils on theworn surface or along the fabricated edges of the productExperimentation indicated that controlled surface deorien-tation would eliminate these issues An analytical techniquewas required that could determine the level of orientationin multiple axis to allow identification of an effective heat-treating method to achieve surface deorientation as wellas develop control parameters for processing equipmentthat could be applied during the commercial manufacturingprocess

22 Sample Preparation for Micro-Raman Spectroscopy AnOPC board was cut with a saw along the extrusion directionto expose the cross-section that was perpendicular to theheat-treated surface as shown in Figure 1 The cutting direc-tion shown in Figure 1 is vertical but can also be horizontal aslong as it is parallel to the extrusion direction The exposedcross-section was then ground to a smooth flat surface usinggrinding papers of 320 800 1200 2400 and 4000 grit on aStruers Pedemat Rotopol-V polisherwithwater cooling Con-trol experiments using different orientation of samples rela-tive to polishing directionwere carried out to ensure that suchsample preparationmethod does not alter or introduce orien-tation to OPC board cross-sections Polarized Raman spectrawere then collected at various depths as indicated by the reddots on the polished cross-section as shown in Figure 1

23 PolarizedMicro-RamanAnalysis AKaiser Raman RXN1microscope with 785 nm laser excitation was used Aschematic of the Raman optical pathway is shown in Figure 1Multimode optical fibers were used to deliver the laser tothe microscope and the signal back to the spectrometerTwo independent linear polarizers were used to control thepolarization state of the excitation laser and the Ramansignals

Raman signals were collected in the backscattering geom-etry using a 20x long-working-distance objective The laserspot size was approximately 20 120583m in diameter Typical laserpower used was in the range of 30 to 100mW depending onthe pigment loading in a sample It should be noted that laserheating could cause molecular relaxation and even meltingThe exact power used for each spectrumwas generally half of

Journal of Spectroscopy 3

Rotate90∘

Cross-section

Treatedsurface

Extrusiondirection

Laser

Spectrometer

Sample

Cross-section

Treated surfaces

Extrusio

n

Excitation polarizer

Probe head

Collection polarizer

Objective

Sample xy

z

x

y

z

xyz stage

ZZ YY

Figure 1 Schematic illustration of how a board was cut and analyzed by micro-Raman analysis

the power that would cause specimen surface melting Oneminute collection time was used to acquire sufficient signal-to-noise ratio

At each point of a sample two spectra were collected theparallel and the perpendicular The parallel (perpendicular)spectrum is collected with the two polarizers oriented sothat the electric field of the incoming laser beam and theoutgoing signal beam are both parallel (perpendicular) to theextrusion direction It should be noted that that there aremany more geometries that can be used (eg one polarizerparallel to and one polarizer perpendicular to the extrusiondirection or with the sample oriented differently) but theparallel and perpendicular spectra collected in the mannerdescribed above can best reflect the orientation differences ina sample

3 Results and Discussion

31 Control Samples Figure 3 compares the parallel andperpendicular spectra collected from a plastic pellet of thesame material used in the composite formulation (top panel)and from an oriented fiber of the same material (bottompanel) For this specific sample polypropylene was used asthe plastic component of the composite Details in the peakassignments for PP have previously been reported and willnot be repeated here [13 14] It is obvious that while the par-allel and perpendicular spectra are almost indistinguishablefor the PP pellet sample (note all spectra are normalized tothe strongest peak within each panel) dramatic differencescan be found for the parallel and perpendicular spectra of PPfibers

Such differences in the spectra collected with differentpolarizers are commonly observed for most oriented poly-mers and several examples are shown in Figure 3 The extentof differences exhibited by the parallel and perpendicularspectra depends on several factors such as the level oforientation within themacromolecular chain the orientationof a functional group relative to its polymer backboneand the Raman tensor of the functional group As can beobserved in Figure 3 spectral differences present between

the parallel and perpendicular spectra range from dramaticfor polyethylene and poly(vinylidene fluoride-co-polyester)fibers to intermediate for polybutene-1 fibers and to quitesubtle for poly(styrene-co-acrylonitrile) fibers OR shouldnot be used to directly compare the level of orientation acrossdifferent polymers and rather should only be used as a relativemeasure to evaluate molecular orientation level for uniaxiallyoriented samples of the same polymer Discussion below willbe focused on the PP orientation in OPC boards

According to (1) two bands need to be selected for thecalculation of OR for each phase For the PP investigatedhere both the crystalline and the amorphous phases arepresent in significant amount and therefore two sets ofbands should be used one set for each phase [15] Belowwe will focus on the orientation characterization of thecrystalline phase because a similar trend was observed forthe amorphous phase The baseline-corrected peak height ofthe 809 cmminus1 peak and the 841 cmminus1 peak is used as 1198681 and1198682 respectively as used in several previous studies [16ndash18] Inthe next sections line maps small-area mapping and large-areamappingwill be shown for the PPOPC samples with andwithout surface treatment

32 Line Maps For consistency PP OPC cross-section sam-ples are always oriented the same way in reference to the labcoordinate system with the extrusion direction parallel to themicroscope stage as shown in Figure 1 Two line maps werecollected one parallel and one perpendicular A stable stage iscritical to ensure that the corresponding parallel and perpen-dicular spectra in the two line maps are from the same spotSpectra in these line maps were collected from evenly spacedpoints on an OPC cross-section spanning from the surfaceinto the core The OR profiles from three representativesamples are shown in Figure 4 Samples (a) (b) and (c) werefrom similar OPC boards but after different level of surfacetreatments aimed to cause orientation relaxation with (a)receiving no surface treatment (b) an intermediate level and(c) the highest level of surface treatment Before we comparethe OR profiles in Figure 4 it is worth noting that the ORfor the PP fiber shown in Figure 2 is calculated to be 77


0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)

Raman shift (cmminus1)

PP pellet ZZPP pellet YY

(a)

0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)


PP fiber ZZPP fiber YY

(b)

Figure 2 (a) 119885119885 and 119884119884 spectra of a PP pellet (b) 119885119885 and 119884119884 spectra of a PP fiber

0

05

1

15

2

25

3

35

4

45

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)


Poly(styrene-co-acrylonitrile)

Poly(vinylidene fluoride-co-polyester)

Polyethylene

Polybutene-1

ZZ

YY

Figure 3 Comparison of 119885119885 to 119884119884 spectra of (from top tobottom) poly(styrene-co-acrylonitrile) poly(vinylidene fluoride-co-polyester) poly(1-butene) and polyethyelene

and about 1 for the PP pellet The values of 77 and 1 arespecific for the particular bands selected (841 and 809 cmminus1)and other choices of bands may also be valid but will havedifferent OR valuesTheOR ratio calculated using the samepair of bands for PP in OPC can be compared It is unlikelyfor the OR value for PP in an extrusion oriented sampleto reach as high as 77 as very high draw ratio is neededfor completely relaxed PP samples its OR will be close to1 as the polarization should not affect the Raman spectra ofisotropic materials If somehow the PP chain has a preferredorientation in the transverse direction then an OR smallerthan 1 will be observed Samples with OR value of 119909 and1119909 should have the same level of orientation but with theorientation direction orthogonal to each other

Given the above information it is clear from Figure 4that while the inner region of all three samples is relatively

orientated with OR ranging from 25 to 4 their surface ori-entation exhibited dramatic differences Sample (a) showedno relaxed orientation at the surface because it did not receiveany surface treatment Samples (b) and (c) both showedpartially relaxed surface region with OR ranging between 1and 16 but the relaxed surface layer is only about 110 120583m forSample (b) much thinner than the 380 120583m thick relaxed skinof Sample (c) Such observations are in good agreement withthe sample treatment history and provided an effective way tounderstand how efficient the treatment is in relaxing polymerorientation

33 Small-Area Maps The above line map methods can bereadily applied to acquire an area map of PP orientation ifthe area of interest can fit within the range of the microscopestage It is critical for the OPC cross-section surface to behorizontal and parallel to the stage to ensure that all the spotsin the map are in focus The results shown in Figure 5 werefrom a surface-treated OPC cross-section with its surfaceon the right edge of the map Spectra were collected in araster-scan fashion from an area of 600120583m (along the depthdirection) times 1000 120583m (along the extrusion direction)The reddots in Figure 5 right panel represent the spectral collectionspots which formed a 26 times 8 grid with 26 evenly spaced linesdistributed along the depth direction and 8 evenly spacedlines distributed along the extrusion direction Such a formof grid was chosen in order to capture the sharp transitionbetween the skin and core region and because less dramaticchange in OR was expected along the extrusion directionThe map in Figure 5 indeed confirms this expectation andclearly shows that the skin layer was relatively uniform with athickness on the order of 200 to 250 120583mThe false-color mapin the left panel of Figure 5 was generated by interpolating theOR over the 26 times 8 grid

34 Large-Area Mapping While the results above clearlydemonstrate the power of polarized micro-Raman analysisto characterize the surface relaxation the orientation dis-tribution across the entire OPC product cross-section iswhat determines the overall mechanical strength of an OPC


4

35

3

25

2

15

1

05

0

0 50 100 150 200 250

OR

(au

)

Depth (120583)

(a)

45

4

35

3

25

2

15

1

05

0

0 100 200 300 400 500

OR

(au

)

Depth (120583)

(b)

0 200 400 600

Depth (120583)

OR

(au

)

45

4

35

3

25

2

15

1

05

0

(c)

Figure 4 Line maps of OR profiles collected from the surface region of three different samples with (a) no (b) medium level and (c) highlevel of surface treatment

x-axis (120583m)

y-a

xis (120583

m)

0

200

400

600

800

1000

0 200 400 600

OR

Cross-section

Treatedsurface

Depth direction

Extrusiondirection

1000120583m

600120583m

35

3

25

2

15

1

05

Figure 5 Mapping of orientation for a 600 times 1000 120583m area as marked by the shaded area with red dots representing the spectral collectionspots


structure Many interdependent factors can influence thefinal strength of an OPC product such as the die designtemperature feed rate cooling rate and fillers and it is oftendifficult to understand how these various factors can lead tofinal product performance without first understanding howthey influence the molecular orientation

Figure 6 illustrates how the large-area orientation map-ping was carried out An OPC sample was cut into 11 verticalsections and line maps were carried out on each sectionas represented by the red dots The sample can also becut into horizontal sections However due to the samplegeometry horizontal sections are thin and thus more proneto deformations

The orientation mapping results from two representativesamples are shown in the bottom panel of Figure 6 OPCsample 1 was a regular product while a side slot was builtinto OPC sample 2 according to its design The orienta-tion mapping yields a direct and visual way to understandthe level of orientation at various regions within an OPCproduct Both samples showed similar general patterns asurface skin region on the top and bottom of the productthat underwent relaxation during surface treatment a rela-tively oriented region beyond the skin and a relaxed coreregion

For OPC sample 1 the entire orientation map showsremarkable symmetry along both the horizontal and verticalmiddle line with the oriented outer layer about 25 cm or1 inch thick (excluding the relaxed surfacewhichwas orientedprior to surface treatment) surrounding the core region andwith the core region showing a gradient of OR which can befurther used to define an inner and outer core region Such adistribution of orientation supports the hypothesis that thecore region due to insulation by the outer layer has moretime to relax than the material in the outer layer In contrastthe outer region cools down faster and thus effectively locksthemolecular orientation once the sample temperature dropsbelow 119879119898 or 119879119892 Analysis using micro-Raman technologyprovides an improved understanding of how process condi-tions can be related to molecular orientation and ultimatelyto product performance which is thus achieved OPC sample2 shows an orientation map that is rather different fromOPCsample 1This sample appeared to be less oriented overallTheexact reasons behind such differences are of great interest toengineers and material scientists but are beyond the scope ofthis study

4 Conclusions

In this studywe used polarizedmicro-Raman spectroscopy tostudy PP morphology and orientation in uniaxially orientedOPC products in order to guide the posttreatment of PPcomposite products We applied this method to analyze PPOPC and the results from the surface region enable usto correlate the surface treatment parameters to the levelof skin orientation relaxation and skin thickness and theresults from the large scale mapping show in a visual wayhow process conditions can influence the molecular orien-tation across the entire cross-section of an OPC material

22

mm

Extrusion direction

059984001998400

1599840025998400

3998400

35998400 4998400

45998400

5998400

2

13mm

(a)

20

10

0

10 20 30 40 50

Dep

th (120583

)

25

20

15

10

5

0

10 20 30 40 50

Inches from side

Dep

th (120583

)

Inner coreOuter coreOuter layer

OPC board 1

OPC board 2

Inches from side

times103

times103

le1500

le2000

le2500

le3000

le3500

gt3500

OR

(b)

Figure 6 (a) A schematic illustration of how an OPC board is cutinto sections (b) Orientationmap of twoOPC boards OR is color-coded

The methodologies described here can be readily applied toother polymeric systems

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors would like to thank theDowChemical Companyand Eovations LLC for permission to publish this workHelp in sample preparation from Robbie Samson is gratefullyacknowledgedThey also appreciate the inspiring discussionswith Robert Cieslinski and Kevin Nichols


References

[1] L K Tamm and S A Tatulian ldquoInfrared spectroscopy of pro-teins and peptides in lipid bilayersrdquo Quarterly Reviews ofBiophysics vol 30 no 4 pp 365ndash429 1997

[2] M Tanaka and R J Young ldquoReview Polarised Raman spec-troscopy for the study of molecular orientation distributions inpolymersrdquo Journal of Materials Science vol 41 no 3 pp 963ndash991 2006

[3] R Ikeda B Chase and N J Everall ldquoBasics of orientation mea-surements in Infrared and Raman spectroscopyrdquo in Handbookof Vibrational Spectroscopy John Wiley amp Sons 2006

[4] T G Zhang C H Zhang and G K Wong ldquoDeterminationof molecular orientation in molecular monolayers by second-harmonic generationrdquo Journal of the Optical Society of AmericaB vol 7 no 6 pp 902ndash907 1990

[5] M B Feller W Chen and Y R Shen ldquoInvestigation ofsurface-induced alignment of liquid-crystal molecules by opti-cal second-harmonic generationrdquo Physical ReviewA vol 43 no12 pp 6778ndash6792 1991

[6] X Chen M L Clarke J Wang and Z Chen ldquoSum frequencygeneration vibrational spectroscopy studies on molecular con-formation and orientation of biological molecules at interfacesrdquoInternational Journal of Modern Physics B vol 19 no 4 pp 691ndash713 2005

[7] Z Chen Y R Shen and G A Somorjai ldquoStudies of polymersurfaces by sum frequency generation vibrational spectroscopyrdquoAnnual Review of Physical Chemistry vol 53 pp 437ndash465 2002

[8] X Chen J Wang A P Boughton C B Kristalyn and Z ChenldquoMultiple orientation of melittin inside a single lipid bilayerdetermined by combined vibrational spectroscopic studiesrdquoJournal of the American Chemical Society vol 129 no 5 pp1420ndash1427 2007

[9] G A Voyiatzis and K S Andrikopoulos ldquoFast monitoringof the molecular orientation in drawn polymers using micro-Raman spectroscopyrdquo Applied Spectroscopy vol 56 no 4 pp528ndash535 2002

[10] C Minogianni K G Gatos and C Galiotis ldquoEstimation ofcrystallinity in isotropic isotactic polypropylene with Ramanspectroscopyrdquo Applied Spectroscopy vol 59 no 9 pp 1141ndash11472005

[11] R M Khafagy ldquoIn situ FT-Raman spectroscopic study of theconformational changes occurring in isotactic polypropyleneduring its melting and crystallization processesrdquo Journal ofPolymer Science Part B Polymer Physics vol 44 no 15 pp2173ndash2182 2006

[12] J J OrsquoBrien T O Kirch K L Nichols and B M BirchmeierldquoOriented polymer composition with a deoriented surfacelayerrdquo US8475700 B2 2010

[13] M C Tobin ldquoThe infrared spectra of polymers IIIThe infraredand Raman spectra of isotactic polypropylenerdquo The Journal ofPhysical Chemistry vol 64 no 2 pp 216ndash219 1960

[14] P D Vasko and J L Koenig ldquoRaman scattering and polarizationmeasurements of isotactic polypropylenerdquoMacromolecules vol3 no 5 pp 597ndash601 1970

[15] R P Paradkar A Leugers R Patel X Chen G Meyers andE Lipp ldquoRaman spectroscopy of polymersrdquo in Encyclopedia ofAnalytical Chemistry John Wiley amp Sons New York NY USA2006

[16] D Garcıa-Lopez J C Merino I Gobernado-Mitre and J MPastor ldquoPolarized confocal Raman microspectroscopy studies

of chain orientation on injected poly(propylene)montmoril-lonite nanocompositesrdquo Journal of Applied Polymer Science vol96 no 6 pp 2377ndash2382 2005

[17] X Wang and S Michielsen ldquoIsotactic polypropylene morphol-ogy-Raman spectra correlationsrdquo Journal of Applied PolymerScience vol 82 no 6 pp 1330ndash1338 2001

[18] K Aratake M Taniguchi and H Ito ldquoPolyolefin fiber and non-woven fabric produced by using the samerdquo Patent US5910362A 1999

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more information For example the second and fourth termsof the orientation distribution function characterized byLegendre polynomial ⟨1198752(cos 120579)⟩ and ⟨1198754(cos 120579)⟩ can be cal-culated for vibrational modes whose Raman tensor is known[2 3] Other higher order spectroscopy techniques such assecond harmonic generation (SHG) [4 5] and sum frequencygeneration vibrational spectroscopy (SFG) [6ndash8] have alsobeen shown to provide insights into molecular orientationespecially when combined with linear spectroscopy tech-niques such as IR or Raman Their complex instrumentationand data analysis and surfaceinterface-specific nature havelimited their applications mostly to academic settings

Here we describe an industrial application of polarizedRaman spectroscopy to characterize the molecular orien-tation of polymers within an oriented composite materialwith uniaxial orientation It is demonstrated that through theuse of orientation ratio (OR (1)) the molecular orientationof OPC can be effectively characterized on length scalespanning from 120583m scale to macroscopic scale thus enablingthe mapping of orientation across the entire cross-section ofan OPC sample OR is defined in (1) where 1198681 stands for theintensity of a band that is sensitive to polarization while 1198682stands for the intensity of another band that is insensitive topolarization or shows the opposite trend The 119885119885 and 119884119884 inthe subscript denote whether the spectrum is collected withthe electric field of the excitationcollection beam parallel orperpendicular to the extrusion direction of the sample (seeFigure 1)

OR =11986811198851198851198682119885119885

11986811198841198841198682119884119884

(1)

Although this approach does not yield detailed quantita-tive orientation distribution functions as the more elab-orate polarized Raman methods previously developed itssimplicity and robustness make it suitable for industrialapplications where most samples have many nonpolymercomponents such as additives fillers and pigments VoyiatzisandAndrikopoulos showed that despite the use of calibrationcurve the OR can potentially be correlated to the variousterms of the orientation distribution function [9] Thiswas not necessary for the applications investigated hereinVoyiatzis and Andrikopoulos also demonstrated that forwell-behaved systems such as a dye dissolved in polymericmatrix the orientation of the dyemolecules can be effectivelycharacterized by a simple ratio of 11986811199111199111198682119911119911 which enablesfast monitoring of orientation during a drawing process Theassumptions behind this approachmay not always be satisfiedby many industrial OPC samples For example difference incrystallinity may be another factor that may cause a changein the 11986811199111199111198682119911119911 ratio [10 11] The 11986811199101199101198682119910119910 term in thedenominator of the OR equation can effectively accountfor the variation of other factors such as crystallinity andconcentration

2 Materials and Methods

21 OPC Board Production The details on the OPC extru-sion and processing can be found in previous patents [12]

An appropriate formulation consisting of both miscible andnonmiscible components is extruded into a profile usingstandard material feeding and extruding technology Theextruded profile is then uniaxially drawn using a drawing diein a temperature controlled environment The ratio of theproduct dimensions before and after drawing is known asthe drawing ratio As the drawing ratio is increased towardsits optimum value density tends to decrease while productstiffness defined by flexural modulus and elasticity tends toincrease

Use of high draw ratios tends to produce productswith high degrees of surface orientation While the level oforientation generates many useful properties for the orientedpolymer composite high surface orientation causes issueswhen the productrsquos surface undergoes surface wear or theproduct is cut to specific lengths or shapes As noted earlierthe high degree of orientation tends to generate fibrils on theworn surface or along the fabricated edges of the productExperimentation indicated that controlled surface deorien-tation would eliminate these issues An analytical techniquewas required that could determine the level of orientationin multiple axis to allow identification of an effective heat-treating method to achieve surface deorientation as wellas develop control parameters for processing equipmentthat could be applied during the commercial manufacturingprocess

22 Sample Preparation for Micro-Raman Spectroscopy AnOPC board was cut with a saw along the extrusion directionto expose the cross-section that was perpendicular to theheat-treated surface as shown in Figure 1 The cutting direc-tion shown in Figure 1 is vertical but can also be horizontal aslong as it is parallel to the extrusion direction The exposedcross-section was then ground to a smooth flat surface usinggrinding papers of 320 800 1200 2400 and 4000 grit on aStruers Pedemat Rotopol-V polisherwithwater cooling Con-trol experiments using different orientation of samples rela-tive to polishing directionwere carried out to ensure that suchsample preparationmethod does not alter or introduce orien-tation to OPC board cross-sections Polarized Raman spectrawere then collected at various depths as indicated by the reddots on the polished cross-section as shown in Figure 1

23 PolarizedMicro-RamanAnalysis AKaiser Raman RXN1microscope with 785 nm laser excitation was used Aschematic of the Raman optical pathway is shown in Figure 1Multimode optical fibers were used to deliver the laser tothe microscope and the signal back to the spectrometerTwo independent linear polarizers were used to control thepolarization state of the excitation laser and the Ramansignals

Raman signals were collected in the backscattering geom-etry using a 20x long-working-distance objective The laserspot size was approximately 20 120583m in diameter Typical laserpower used was in the range of 30 to 100mW depending onthe pigment loading in a sample It should be noted that laserheating could cause molecular relaxation and even meltingThe exact power used for each spectrumwas generally half of


Rotate90∘

Cross-section

Treatedsurface

Extrusiondirection

Laser

Spectrometer

Sample

Cross-section

Treated surfaces

Extrusio

n


Probe head


Objective

Sample xy

z

x

y

z

xyz stage

ZZ YY











0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)



(a)

0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)



(b)


0

05

1

15

2

25

3

35

4

45

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)




Polyethylene

Polybutene-1

ZZ

YY








4

35

3

25

2

15

1

05

0

0 50 100 150 200 250

OR

(au

)

Depth (120583)

(a)

45

4

35

3

25

2

15

1

05

0

0 100 200 300 400 500

OR

(au

)

Depth (120583)

(b)

0 200 400 600

Depth (120583)

OR

(au

)

45

4

35

3

25

2

15

1

05

0

(c)


x-axis (120583m)

y-a

xis (120583

m)

0

200

400

600

800

1000

0 200 400 600

OR

Cross-section

Treatedsurface

Depth direction

Extrusiondirection

1000120583m

600120583m

35

3

25

2

15

1

05







4 Conclusions


22

mm

Extrusion direction

059984001998400

1599840025998400

3998400

35998400 4998400

45998400

5998400

2

13mm

(a)

20

10

0

10 20 30 40 50

Dep

th (120583

)

25

20

15

10

5

0

10 20 30 40 50

Inches from side

Dep

th (120583

)


OPC board 1

OPC board 2

Inches from side

times103

times103

le1500

le2000

le2500

le3000

le3500

gt3500

OR

(b)





Acknowledgments



References





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Rotate90∘

Cross-section

Treatedsurface

Extrusiondirection

Laser

Spectrometer

Sample

Cross-section

Treated surfaces

Extrusio

n


Probe head


Objective

Sample xy

z

x

y

z

xyz stage

ZZ YY











0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)



(a)

0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)



(b)


0

05

1

15

2

25

3

35

4

45

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)




Polyethylene

Polybutene-1

ZZ

YY








4

35

3

25

2

15

1

05

0

0 50 100 150 200 250

OR

(au

)

Depth (120583)

(a)

45

4

35

3

25

2

15

1

05

0

0 100 200 300 400 500

OR

(au

)

Depth (120583)

(b)

0 200 400 600

Depth (120583)

OR

(au

)

45

4

35

3

25

2

15

1

05

0

(c)


x-axis (120583m)

y-a

xis (120583

m)

0

200

400

600

800

1000

0 200 400 600

OR

Cross-section

Treatedsurface

Depth direction

Extrusiondirection

1000120583m

600120583m

35

3

25

2

15

1

05







4 Conclusions


22

mm

Extrusion direction

059984001998400

1599840025998400

3998400

35998400 4998400

45998400

5998400

2

13mm

(a)

20

10

0

10 20 30 40 50

Dep

th (120583

)

25

20

15

10

5

0

10 20 30 40 50

Inches from side

Dep

th (120583

)


OPC board 1

OPC board 2

Inches from side

times103

times103

le1500

le2000

le2500

le3000

le3500

gt3500

OR

(b)





Acknowledgments



References





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)



(a)

0

02

04

06

08

1

12

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)



(b)


0

05

1

15

2

25

3

35

4

45

350 550 750 950 1150 1350 1550

Inte

nsity

(au

)




Polyethylene

Polybutene-1

ZZ

YY








4

35

3

25

2

15

1

05

0

0 50 100 150 200 250

OR

(au

)

Depth (120583)

(a)

45

4

35

3

25

2

15

1

05

0

0 100 200 300 400 500

OR

(au

)

Depth (120583)

(b)

0 200 400 600

Depth (120583)

OR

(au

)

45

4

35

3

25

2

15

1

05

0

(c)


x-axis (120583m)

y-a

xis (120583

m)

0

200

400

600

800

1000

0 200 400 600

OR

Cross-section

Treatedsurface

Depth direction

Extrusiondirection

1000120583m

600120583m

35

3

25

2

15

1

05







4 Conclusions


22

mm

Extrusion direction

059984001998400

1599840025998400

3998400

35998400 4998400

45998400

5998400

2

13mm

(a)

20

10

0

10 20 30 40 50

Dep

th (120583

)

25

20

15

10

5

0

10 20 30 40 50

Inches from side

Dep

th (120583

)


OPC board 1

OPC board 2

Inches from side

times103

times103

le1500

le2000

le2500

le3000

le3500

gt3500

OR

(b)





Acknowledgments



References





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


4

35

3

25

2

15

1

05

0

0 50 100 150 200 250

OR

(au

)

Depth (120583)

(a)

45

4

35

3

25

2

15

1

05

0

0 100 200 300 400 500

OR

(au

)

Depth (120583)

(b)

0 200 400 600

Depth (120583)

OR

(au

)

45

4

35

3

25

2

15

1

05

0

(c)


x-axis (120583m)

y-a

xis (120583

m)

0

200

400

600

800

1000

0 200 400 600

OR

Cross-section

Treatedsurface

Depth direction

Extrusiondirection

1000120583m

600120583m

35

3

25

2

15

1

05







4 Conclusions


22

mm

Extrusion direction

059984001998400

1599840025998400

3998400

35998400 4998400

45998400

5998400

2

13mm

(a)

20

10

0

10 20 30 40 50

Dep

th (120583

)

25

20

15

10

5

0

10 20 30 40 50

Inches from side

Dep

th (120583

)


OPC board 1

OPC board 2

Inches from side

times103

times103

le1500

le2000

le2500

le3000

le3500

gt3500

OR

(b)





Acknowledgments



References





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






4 Conclusions


22

mm

Extrusion direction

059984001998400

1599840025998400

3998400

35998400 4998400

45998400

5998400

2

13mm

(a)

20

10

0

10 20 30 40 50

Dep

th (120583

)

25

20

15

10

5

0

10 20 30 40 50

Inches from side

Dep

th (120583

)


OPC board 1

OPC board 2

Inches from side

times103

times103

le1500

le2000

le2500

le3000

le3500

gt3500

OR

(b)





Acknowledgments



References





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


References





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article orientation mapping of extruded polymeric...

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