The influence of sizings on the durability of high-temperature polymer composites

The Influence of Sizings on the Durability of

High-Temperature Polymer Composites

RONALD E.ALLRED4

SHELDON P.WESSON

Adherent T echnologies,Inc.,Albuquerque,NM,USA

E.EUGENE SHIN

LINDA INGHRAM

LINDA MCCORKLE

Ohio Aerospace Institute,Cleveland,OH,USA

DEMETRIOS PAPADOPOULOS

University ofAkron,Akron,OH,USA

DONALD WHEELER

JAMES K.SUTTER

NASA Glenn Research Center,Cleveland,OH,USA

(Received18April2003;accepted6May2003)

Abstract:T o increase performance and durability of high-temperature composites for potential rocket en-gine components,it is necessary to optimize wetting and interfacial bonding between high-modulus carbon fibers and high-temperature polyimide resins.Sizings commercially supplied on most carbon fibers are not compatible with polyimides.In this study,the chemistry of sizings on two high-modulus carbon fibers (M40J and M60J,T oray)was characterized as was the chemistry of PMR-II-50fluorinated polyimide resin. The carbon fibers were characterized using single filament wetting,scanning electron microscopy,Fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopic measurements.The polyimide ma-trix resins were coated onto glass filaments for characterization by wetting measurements.Surface energy components were obtained by wetting with nondispersive(methylene iodide),acidic(ethylene glycol),and basic(formamide)probes.A continuous desizing system that uses an environmentally friendly chemical-mechanical process was developed for tow level https://www.wendangku.net/doc/5619185758.html,posites were fabricated with fibers containing the manufactureròs sizing,desized,and further treated with a reactive finish.Results of room tempera-ture tests after thermal aging show that the reactive finish produces a higher strength and more durable interface compared to the manufactureròs sizing.When exposed to moisture blistering tests,however,the better-bonded composite displayed a tendency to delaminate,presumably due to trapping of volatiles.

Key W ords:Sizing,desizing,carbon fibers,reactive finish,thermal aging,mechanical properties,wetting,sur-face energy,blistering,interface

High Performance Polymers, 395?419,2003

f?2003Sage Publications

396R.E.ALLRED ET AL.

1.INTRODUCTION

High-temperature polymer matrix composites(PMCs)are desired for many aerospace and military applications.These aggressive environments have required new blends of materials properties in the composite fiber and matrix.In that endeavor,it is often found that the sizings routinely added to commercial carbon fibers are not compatible with the new high-temperature matrix resins.The result is that the thermo-oxidative stability(TOS) and mechanical properties of composites made with such fibers are compromised.Before high-temperature PMCs can routinely be used in demanding applications,their long-term TOS must be improved.

M40J and M60J carbon fibers available from T oray(Japan)have an unusual combination of stiffness and strength for use in high-temperature applications;however, the epoxy-compatible sizes available on these fibers may not be optimum for compatibility with high-temperature polymers.The work described here was undertaken to characterize the T oray size,to develop a means to remove the commercial size and replace it with a high-temperature finish,and to determine the thermomechanical properties of polyimide composites fabricated with the various fiber surface types.Our approach was to characterize the M40J and M60J sizings using scanning electron microscopy (SEM),single filament wetting,X-ray photoelectron spectroscopy(XPS),and Fourier transform infrared spectroscopy(FTIR).The T oray sizing was then removed using hot chloroform in a continuous desizing process and a high-temperature finish applied and characterized.The desized and desized/refinished fibers were also characterized using the above techniques.Cross-plied composites were fabricated with PMR-II-50matrices and tested in the thermally aged and unaged conditions.Finally,moisture blistering tests were conducted on the various laminates.

Results show that the T oray sizing is very non-uniform on the fiber surface and that it appears to be a hydroxyllated terephthalate type of polyester.Desizing in hot chloroform with ultrasound leaves mostly clean fiber with a few small(tenths of microns)nodules of residual size.The desized T oray fibers are also highly striated,creating the possibility of improved interfacial adhesion by a mechanical interlocking mechanism.Single filament wetting has shown that the sized surfaces are energetically and topographically heterogeneous.Formamide wetting shows that M40J and M60J surfaces display similar acidity whether sized or desized.Ethylene glycol wetting suggests that the size covers basic functionality that is uncovered by desizing.PMR-II-50polyimide resin is mildly amphoteric,since the acid-base component of fiber wettability(Z d e)is small but finite for both acidic and basic probe liquids.The reactive finish bonds well to the desized fiber and improves interfacial adhesion before and after high-temperature aging;however,the well bonded laminates debonded in the moisture blistering tests,presumably due to internal trapping of volatiles.

SIZINGS AND DURABILITY OF HIGH-TEMPERATURE PMC397

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2.EXPERIMENT AL PROCEDURES

2.1.Desizing approach

Initial desizing studies showed that1,3,and5minutes in boiling chloroform dropped the surface oxygen content to a constant level of approximately10%.These data were used to design a continuous desizing unit shown schematically in Figure1.The desizing unit shown in Figure1consists of a7m heated tube feeding in and out of each side of a bath that is irradiated with ultrasound.The entire system is filled with chloroform.For application of reactive finish,a dip bath followed by a tube furnace is placed between the desizing unit and the take-up winder.The desizing unit was operated at a speed of3m/minute. Additional information on the desizing process is given in Allred et al.[1].

2.2.W etting experiments

Fiber surface energy characterization was performed using the Wilhelmy technique[2]. M40J and M60J carbon monofilaments were glued to metal hooks and suspended vertically from the working arm of a Cahn2000microbalance,while a precision elevator raised and lowered the liquid surface along0.5mm of fiber.A schematic of the wetting apparatus is given in Figure2.

A computer periodically recorded the change in apparent mass caused by wetting forces at the three-phase boundary using the probe liquids listed in T able1.Advancing work of adhesion,Z dgy,the dispersive component of fiber wettability,Z g,and the acid/base component of fiber wettability,Z d e,were computed by methods previously reported[3?6].

Many of the substrate-liquid combinations spread in the receding mode and were close to spreading in the advancing mode.Since non-spreading liquids with known acid/base character,(ethylene glycol and formamide)were carefully selected for having high surface tensions,the number of additional liquid probes that could be used is severely limited.This indicates that,while wetting studies are a valuable method for surface characterization, further characterization of these surfaces requires another technique,such as inverse gas chromatography or microcalorimetry.

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2.3.Reactive finish formulation

The reactive finishes were based on the work in Allred and Sutter[7].That work and subsequent studies by the authors have shown that the reactive coupling agent chemically bonds to carbon fiber surfaces.Figure3depicts the structure of the proprietary9307 coupling agent.

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The finish formulations used0.3%coupling agent and3.0wt.%PMR-II-50polyimide resin in acetone.The tube furnace was set at a temperature of250 C to initiate the bonding reaction with the desized M40J.

2.4.XPS analysis

Sized,desized,and refinished M40J carbon fibers were analyzed by XPS.Survey spectra were taken to examine the as-received surface chemical stoichiometry.High-resolution spectra were taken of significant peaks seen in the survey scans to determine possible surface bonding states.The analyses were run at NASA Glenn Research Center using a Surface Sciences SSX-100spectrometer with an Al K source.C4v high-resolution peaks were averaged over10to15scans using a spot size of300 m5with no flood gun. O4v peaks were averaged over30scans.A Gaussian curve fitting routine was used to resolve high-resolution photopeaks into components based on binding energy references from model compounds[8].The spectra were not charge referenced.

2.5.FTIR analysis

A Nicolet Magna560FTIR spectrometer equipped with a Nic Plan microscope was used to acquire fiber sizing spectra.The microscope was operated in reflectance mode using a32 objective(spot diameter100 ).T ypically100scans were averaged at4cm 4 resolution versus a gold microscope slide.Spectra were corrected for water and carbon dioxide.

https://www.wendangku.net/doc/5619185758.html,posite fabrication

A new process called??tow plate-windingòòwas developed with a modified lathe for the fabrication of all composite panels.The tow plate-winding process is described in detail in Shin et al.[9].The30 30cm laminated composite panels were fabricated by a typical vacuum bagging process in hot-press molding platens(applied pressure:

400R.E.ALLRED ET AL.

3.45MPa)at NASA GRC using optimized PMR-II-50cure cycles after a separate B-staging at204 C(400 F)for1h.All cured panels were then dried and post-cured at371 C(700 F)in air for16hours.The fabricated PMR-II-50matrix panels were [0,90,90,0,90,0,0,90,0,90,90,0]v24-ply composite laminates and approximately0.25cm thick.

Initial quality of the composite panels was evaluated by ultrasonic C-scan (UL TRAP AC-AD-500,Physical Acoustics)with a5MHz probe after a standard calibration with poly(methyl methacrylate).V oid content and fiber volume fraction of the composites were determined by acid digestion per ASTMD-3171.The glass transition temperatures,thermal degradation temperature,coefficient of thermal expansion,and dynamic mechanical properties of the cured and postcured composites were determined by standard thermo-analysis techniques including dynamic mechanical analysis(T A Instrument2980DMA),thermomechanical analysis(T A Instrument2940TMA),and thermogravimetric analysis(T A Instrument2950TGA HR).Composite mechanical properties were measured using an Instron universal testing machine with a Series IX Automated Materials T esting System following ASTM D-3518and D-2344.

2.7.Aging tests

Quarter sections of the laminates were aged in an air circulating oven at343 C(650 F) for various times.Following aging, 78 tensile test specimens and short beam shear specimens were cut using a water-cooled diamond wheel.

Five-cm(2-inch)square blister specimens were sonicated in a cleaning agent and dried in a vacuum oven until constant weight was obtained.The specimens were then conditioned in a humidity cabinet at60 C and90%relative humidity.After the specimens maintained a constant weight,blister testing was performed.The blister tests were performed on the saturated samples at two different conditions.The first condition was at a ramp rate of50 C/min to a temperature of400 C.The second blister condition was obtained at two ramp rates.The first ramp rate of5 C/min was used up to a temperature of250 C then it was increased to a ramp rate of50 C/min to400 C.

Five locations on a sample were marked to measure the thickness change before and after blister testing.A micrometer was used to measure the thickness.The schematic depicting the five locations is shown in Figure4.Corner No.4was cut for photomicrograph,microcrack counts,and void calculation before exposure to humidity conditions.

RESUL TS AND DISCUSSION

3.1.Sized fiber characterization

The appearance of the sized T oray M40J and M60J fibers is shown in Figure5.Figure5 shows that the T oray size is very non-uniform in thickness and coverage on the as-produced fibers.The deep striations on the fiber surface are also seen in Figure5.

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High-resolution XPS C4v photopeaks for the sized T oray fibers are shown in Figure6. Results show that the surface oxygen groups are predominately singly bound to carbon, presumably as hydroxyl moieties.The resolved data are given in T able2.

Results given in T able2show that the T oray sizing has an unusually large amount of oxygen-containing moieties present mostly as single bonded C-O(hydroxyl,ester).The M60J appears to have a somewhat lower size content.

Surface reflectance FTIR spectra for the T oray sized carbon fibers are shown in Figure7.In Figure7,in addition to aliphatic and aromatic C-H stretching bands between 2800and3100cm 4,a broad peak between3200and3600cm 4is seen that is indicative

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of hydroxyl groups.Peaks located at1725?1730indicate aromatic ester carbonyl and peaks at1250and1300are C-O vibrations.It is also evident in Figure7that the sizings on both fibers have the same chemistry.At this point,the balance of the study was focused on the M40J fibers only.

3.2.Desized fiber characterization

The appearance of M40J fibers after treatment in the desizing unit with ultrasound is shown in Figure8.As seen in Figure8,most of the sizing except persistent sub-micron size nodules have been removed by the hot chloroform.High-resolution C4v XPS photopeaks for the sized and desized M40J fiber surface are shown in Figure9.

Resolved XPS data for desized M40J and M60J fibers are given in T able3. Surprisingly,the M60J shows a higher surface oxygen content than the M40J in the desized condition.Generally,the effectiveness of shear treatments on carbon fibers decreases with increasing fiber modulus.

In order to check the consistency of the desizing process,a1kg roll of desized M40J carbon fiber was analyzed using XPS for surface chemistry.XPS results from the beginning(section1),center(section2),and end(section3)of the roll are given in T able4.

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The percent oxygen results from T able4show that the fiber surface contains11.7 1.65%oxygen.The standard deviation is near the normal error expected for XPS measurements,which shows that the desizing process is consistent over time.

SIZINGS AND DURABILITY OF HIGH-TEMPERATURE PMC405

3.3.Single filament wetting

W etting measurements were used to determine the acid/base component of wetting work of adhesion for the sized and desized M40J carbon fibers.W ork of adhesion measurements with methylene iodide were made to determine the dispersive component of surface energy.

W ork of adhesion Z(mN/m)measures the solid/liquid attraction as shown in Figure2. Z is calculated by Equation1.As seen in Equation1,Z is determined by the weight of the entrained meniscus at the fiber/liquid interface:

Z@ M.Pj@s(1)

where M=liquid surface tension;Pj=wetting force;s=solid perimeter.

Z can be resolved into dispersive and acid?base components by wetting with acidic or basic probes(Equation2).

Z@Z g.Z d e(2) The analysis is conducted by wetting with liquid pairs consisting of a dispersive liquid (methylene iodide)and a basic(formamide)or acidic(ethylene glycol)probe(T able1). The dispersive energy of the solid surface is first calculated using Equation3.

g v@Z5@7 PL(3) where g v=dispersive energy of the solid surface;Z=measured work of adhesion; PL= surface tension of methylene iodide.

Then,the dispersive wetting work of adhesion,Z g,is computed using Equation4.

Z g@5

g o. g v

4 5

(4)

where g o=dispersive component of probe surface tension(literature value); g v= computed from methylene iodide wetting.

Then,Z is measured with an acidic or basic probe and Z d e resolved using Equation5.

Z d e@Z Z g(5) A sample wetting trace for formamide on sized M40J is given in Figure10.A similar wetting trace for desized M40J is given in Figure11.

W e know from the theory of wetting that the advancing wetting trace as the fiber penetrates into the wetting liquid is sensitive to low-energy sites and the receding wetting trace is sensitive to high-energy sites.The high-frequency chatter seen in Figures10and 11is caused by alternating sites of different energies(micro-scale heterogeneity).W etting results for the probe liquids on desized T oray M40J carbon fiber are given in T able5.

Calculated results for the acid-base work of wetting adhesion for formamide on sized and desized M40J and M60J carbon fibers are shown in Figure12.Similar results for ethylene glycol wetting are shown in Figure13.

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As seen in Figures12and13,both the M40J and M60J fibers appear very similar in surface energy as sized or desized.This indicates that they contain the same size and have seen a similar shear treatment on the base fiber.Both the sized and desized fibers are mildly acidic(Figure12).The sized fibers have no basic character;however,the desized fibers do exhibit a basic character(Figure13)and are,thus,amphoteric.

Results for wetting work of adhesion on PMR-II-50are given in Figure14.As seen in Figure14,the PMR-II-50resin is also amphoteric,indicating that it should adhere to the desized fibers by acid-base interactions at the interface.

3.4.Finished fiber characterization

The appearance of the as-finished fiber surfaces is shown in Figure15.The finish goes on in a uniform coating due to the excellent film-forming nature of the PMR-II-50polyimide resin.

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An XPS survey spectrum of the desized and refinished M40J fibers is shown in Figure16.The strong fluorine peak from the PMR-II-50polyimide in the finish is readily evident in Figure16.Figure17shows an XPS survey spectrum for the finished M40J fibers after a1-hour reflux in methanol.The strong remaining fluorine peak in Figure17 shows that the finish,including the PMR-II-50polyimide resin is well bonded to the M40J fiber surface.

The XPS data on the finished fibers compared to PMR-II-50polyimide resin is given in tabular form in T able6.Only13%of the surface fluorine in the finish was removed by the1-hour methanol reflux.Methanol is an excellent solvent for PMR-II-50and is usually the solvent of choice for synthesis of the polyimide.As such,the large amount of residual resin remaining on the fiber surface is an indirect indication that the finish is chemically bonded to the M40J carbon fiber.

https://www.wendangku.net/doc/5619185758.html,posite laminate characterization and aging

Thermomechanical characterization data for the three laminate types showed matrix W H values at approximately390 C.Microcracks and void content of the as-fabricated laminates are given in T able7.The different fiber surfaces lead to a wide range of microcrack densities,with the low-temperature sizing being the highest.A range of void contents were also observed with the refinished laminates having more than twice the voids of the laminates with sized fibers.

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Thermal aging weight loss data given in Figure18shows the desized laminates to be the least stable while the laminates with refinished fibers exhibited the lowest weight loss, which is an indication of improved TOS imparted by the reactive finish.

412R.E.ALLRED ET AL.

https://www.wendangku.net/doc/5619185758.html,posite mechanical properties

T ensile shear and short beam shear tests were run on specimens from each of the laminates as fabricated and after thermal aging for250and400h at343 C(650 F).The 45 tensile shear strengths as a function of percent return from the C-scans are plotted in Figure19. The data given in Figure19are summarized in Figure20.These results show that the refinished fibers have a stronger and more thermally stable interface,whereas the desized fibers have the weakest and least thermally stable interface.The laminates made with fibers treated with the manufactureròs sizing are in between the other two treatments.

Similar trends are seen in the short beam shear data given in Figures21and22; however,the laminates with refinished fibers show a larger than expected drop after thermal aging(Figure22).

3.7.Blister tests

The equilibrium moisture uptake results showed that the T oray-sized laminates absorbed 1.62 0.11%,the desized1.51 0.04%,and the refinished1.48 0.04%.Moisture weight gain versus time is shown for the laminates containing T oray sized and desized/refinished fibers in Figures23and24.

When subjected to the blister tests,the laminates containing the refinished fibers blistered at260 C under both test https://www.wendangku.net/doc/5619185758.html,minates containing desized fibers did not blister under any conditions,whereas the laminates with the T oray sizing only blistered under Condition1.The blister results are shown graphically in Figures25and26.

The specimens showing large displacements in Figures25and26are from laminates with refinished fibers.The microstructures of the laminates with T oray size and the reactive finish as-fabricated and after blister testing are shown in Figures27?30.

Examination of the microcrack density data in T able2and the as-fabricated cross-sections in Figures27and29leads to the hypothesis that the better bonded laminate with the refinished fibers traps volatiles from moisture and matrix thermal degradation internally,causing the eventual blister formation(Figure30).Where a network of microcracks exist that can provide diffusion paths out of the laminate as in the T oray-sized material,blisters do not form(Figure28).This observation may also explain the large drop in short beam shear strength after thermal aging for the laminates with refinished fibers if internal delaminations were caused by trapping of matrix thermal degradation products.

3.CONCLUSIONS

This study characterized T oray M40J and M60J carbon fiber sizings and desized and refinished fibers and laminates fabricated with them.The T oray size coverage is very non-uniform and contains predominantly hydroxyl groups.A continuous desizing apparatus using hot chloroform and ultrasound produced clean fiber.Single filament wetting results show that the sized and desized surfaces are energetically and topographically heterogeneous.Formamide wetting shows that M40J surfaces and M60J surfaces display

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一般过去式 时间状语：yesterday just now (刚刚) the day before three days ag0 a week ago in 1880 last month last year 1. I was in the classroom yesterday. I was not in the classroom yesterday. Were you in the classroom yesterday. 2. They went to see the film the day before. Did they go to see the film the day before. They did go to see the film the day before. 3. The man beat his wife yesterday. The man didn’t beat his wife yesterday. 4. I was a high student three years ago. 5. She became a teacher in 2009. 6. They began to study english a week ago 7. My mother brought a book from Canada last year. 8.My parents build a house to me four years ago . 9.He was husband ago. She was a cooker last mouth. My father was in the Xinjiang half a year ago. 10.My grandfather was a famer six years ago. 11.He burned in 1991

学生造句--Unit 1

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介词后的动词要用—ing形式。介词加代词时，代词要用宾格。例如：give up her（him）这种形式是正确的，而give up she（he）这种形式是错误的。 7.冠词：冠词是指修饰名词，表名词泛指或特指。冠词有a an the 。 8.叹词：叹词表示一种语气。例如：OH. Ya 等 9.连词：连词是指连接两个并列的成分，这两个并列的成分可以是两个词也可以是两个句子。例如：and but or so 。 10.数词：数词是指表示数量关系词，一般分为基数词和序数词 第二章节：英语句子成分 主语：动作的发出者，一般放在动词前或句首。由名词. 代词. 数词. 不定时. 动名词. 或从句充当。 谓语：指主语发出来的动作，只能由动词充当，一般紧跟在主语后面。 宾语：指动作的承受着，一般由代词. 名词. 数词. 不定时. 动名词. 或从句充当. 介词后面的成分也叫介词宾语。 定语：只对名词起限定修饰的成分，一般由形容

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base on的例句

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英语造句大全

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(完整版)主谓造句

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初中英语造句

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The Kite Runner-美句摘抄及造句

《The Kite Runner》追风筝的人--------------------------------美句摘抄 1.I can still see Hassan up on that tree, sunlight flickering through the leaves on his almost perfectly round face, a face like a Chinese doll chiseled from hardwood: his flat, broad nose and slanting, narrow eyes like bamboo leaves, eyes that looked, depending on the light, gold, green even sapphire 翻译：我依然能记得哈桑坐在树上的样子，阳光穿过叶子，照着他那浑圆的脸庞。他的脸很像木头刻成的中国娃娃，鼻子大而扁平，双眼眯斜如同竹叶，在不同光线下会显现出金色、绿色，甚至是宝石蓝。 E.g.: A shadow of disquiet flickering over his face. 2.Never told that the mirror, like shooting walnuts at the neighbor's dog, was always my idea. 翻译：从来不提镜子、用胡桃射狗其实都是我的鬼主意。E.g.:His secret died with him, for he never told anyone. 3.We would sit across from each other on a pair of high

翻译加造句

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改写句子练习2标准答案

The effective sentences:(improve the sentences!) 1.She hopes to spend this holiday either in Shanghai or in Suzhou. 2.Showing/to show sincerity and to keep/keeping promises are the basic requirements of a real friend. 3.I want to know the space of this house and when it was built. I want to know how big this house is and when it was built. I want to know the space of this house and the building time of the house. 4.In the past ten years,Mr.Smith has been a waiter,a tour guide,and taught English. In the past ten years,Mr.Smith has been a waiter,a tour guide,and an English teacher. 5.They are sweeping the floor wearing masks. They are sweeping the floor by wearing masks. wearing masks,They are sweeping the floor. 6.the drivers are told to drive carefully on the radio. the drivers are told on the radio to drive carefully 7.I almost spent two hours on this exercises. I spent almost two hours on this exercises. 8.Checking carefully,a serious mistake was found in the design. Checking carefully,I found a serious mistake in the design.

用以下短语造句

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英语造句

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