Journal of Nanomaterials

Journal of Nanomaterials / 2015 / Article
Special Issue

Applications of Nanomaterials in Multifunctional Polymer Nanocomposites

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Research Article | Open Access

Volume 2015 |Article ID 146718 | 16 pages | https://doi.org/10.1155/2015/146718

Ultradrawing and Ultimate Tenacity Properties of Ultrahigh Molecular Weight Polyethylene Composite Fibers Filled with Nanosilica Particles with Varying Specific Surface Areas

Academic Editor: Bin Li
Received14 Apr 2015
Revised20 Jul 2015
Accepted29 Jul 2015
Published01 Oct 2015

Abstract

Original and/or functionalized nanosilica particles with a quoted specific surface area of 100, 300, and 600 m2/g, respectively, were used to investigate the influence of specific surface areas of nanosilica particles on ultradrawing and ultimate tensile properties of ultrahigh molecular weight polyethylene (UHMWPE), UHMWPE/nanosilica, and UHMWPE/functionalized nanosilica fibers. The specific surface areas of well-dispersed functionalized nanosilica particles in UHMWPE/functionalized nanosilica fibers can positively affect their ultradrawing, orientation, ultimate tensile properties, and “micro-fibrils” morphologies. Excellent orientation and ultimate tensile properties of UHMWPE/nanofiller fibers can be prepared by ultradrawing the UHMWPE/functionalized nanosilica as-prepared fibers with optimal contents of the best prepared functionalized nanosilica particles well dispersing in the as-prepared fibers. The ultimate tensile strength value of the best prepared UHMWPE/functionalized nanosilica drawn fiber reaches 7.6 GPa, which is about 2.3 times of those of the best prepared UHMWPE drawn fiber without addition of any nanofiller. Specific surface area, morphological and Fourier transform infrared analyses of original and functionalized nanosilica particles, and/or investigations of thermal, orientation factor, and ultimate tensile properties of as-prepared and/or drawn UHMWPE/functionalized nanosilica fibers were performed to understand the above improved ultradrawing and ultimate tensile properties of the UHMWPE/functionalized nanosilica as-prepared and/or drawn fibers.

1. Introduction

As a kind of extremely significant and strategic material, ultrahigh molecular weight polyethylene (UHMWPE) fibers have attracted much attention for the last three decades, since they exhibit significantly higher tenacity but lower density values than those of other high performance fibers, such as carbon and aramid fibers [15]. Polyethylene fibers [1, 631] are typical high performance fibers produced using the gel spinning processing method from flexible polymer chains. Remarkable progress has been made in the improvement of these high performance fibers since then; however, the highest tensile strengths and moduli achieved for UHMWPE fibers are still well below the broad range of theoretical tensile strengths and moduli reported for the UHMWPE perfect crystals [1]. The highest tenacity of commercially available UHMWPE fibers reaches as high as 45 g/den [32]; however, this obtained strength is still far below the theoretical achievable strength, 372 g/den reported for the perfect polyethylene crystal [16]. The key element in obtaining high-strength UHMWPE fibers is to find a way to draw the as-prepared gel specimens to an ultrahigh draw ratio after the gel spinning process. The drawability of the as-prepared gel specimens was found to depend significantly on the compositions of solutions from which gels were made [6, 7, 33]. Several authors [1215, 33] reported that the drawing temperature and rate could markedly affect the maximal achievable draw ratio and tensile properties of solution-grown UHMWPE samples. In addition to the gel solution compositions and drawing conditions, it is generally recognized that the conditions used in the formation process after spinning and/or solution casting of gel solutions can also have a significant influence on the morphology, microstructure, and drawing properties of the specimens formed during the above-mentioned processes [7, 9, 14, 1723].

Our recent investigations [2427] found that the achievable draw ratios (achievable ) of UHMWPE/nanofillers as-prepared fibers prepared near the optimal UHMWPE concentration improve to a maximal value as their nanofillers contents reach an optimal value, respectively, in which, the nanofillers (e.g., carbon nanotube (CNT) [24], attapulgite [25], nanosilica and/or their functionalized nanofillers [26], and functionalized bacterial cellulose [27]) with extremely high specific surface areas can serve as efficient nucleation sites and facilitate the crystallization of UHMWPE molecules into crystals but with lower melting temperatures () and/or evaluated smaller crystal thickness () values during their crystallization processes. Presumably, the crystals with lower and/or evaluated smaller values obtained at proper plain and/or modified nanofiller contents can be melted and pulled out of folded lamellar crystals relatively easily during ultradrawing processes and hence this results in higher drawability and orientation of the UHMWPE/nanofillers or UHMWPE/modified nanofillers fibers. The maximal achievable draw ratios of UHMWPE/nanofillers or UHMWPE/modified nanofillers as-prepared fiber specimens and the tensile strengths of the drawn UHMWPE/nanofillers or UHMWPE/modified nanofillers fiber specimens are significantly higher than those of the plain UHMWPE as-prepared and drawn fiber specimens prepared at the same draw ratios of UHMWPE concentrations but without addition of the nanofillers and/or modified nanofillers, respectively. The ultimate tensile strength values of UHMWPE/purified attapulgite, UHMWPE/functionalized CNT, UHMWPE/functionalized nanosilica, and UHMWPE/functionalized bacterial cellulose drawn fibers prepared using one-stage drawing process at 95°C can reach 4.7, 5.8, 7.0, and 7.1 GN m−2, respectively, which is about 1.74, 2.15, 2.59, and 2.63 times of that of the corresponding plain UHMWPE drawn fibers prepared at the same optimal UHMWPE concentration, formation, and drawing condition but without incorporation of modified nanofillers.

The above results clearly suggested that nanofillers with high specific surface areas can serve as efficient nucleation sites for crystallization of UHMWPE molecules and improve the ultradrawing and ultimate tensile properties of UHMWPE/nanofiller fibers. Among these nanofillers, nanosilica particles are cheap and commercially available for a wide range of specific surface areas. In this study, the ultradrawing and ultimate tensile properties of the UHMWPE/nanosilica and UHMWPE/functionalized nanosilica fibers with a wide range of specific surface areas were systematically investigated. The maximal achievable and ultimate tensile strength values obtained for the best prepared UHMWPE/functionalized nanosilica as-prepared fibers are even higher than those of the best prepared UHMWPE/modified attapulgite, UHMWPE/functionalized CNT, and UHMPE/functionalized bacterial cellulose as-prepared fibers prepared at the optimal modified attapulgite, functionalized CNT, and functionalized bacterial cellulose contents, respectively [2427]. Specific surface area, morphological and Fourier transform infrared analyses of the original and functionalized nanosilica specimens, and/or investigations of thermal, orientation factor, and ultimate tensile properties of the as-prepared and drawn UHMWPE/functionalized nanosilica fiber specimens were performed to understand the above improved ultradrawing and ultimate tensile properties of the UHMWPE/functionalized nanosilica as-prepared and/or drawn fibers.

2. Experimental

2.1. Materials and Sample Preparation

The UHMWPE GUR-4120 resin used in this study is associated with a weight average molecular weight (Mw) of 5.0 × 106, which was kindly supplied by Celanese (Nanjing) Diversified Chemical Corporation, Nanjing, China. Three types of nanosilica particles (Merck SSA-100, SSA-300, and SSA-600) used in this study were purchased from Lu Ming Nanomaterials Corporation, Dalian, China. The specific surface areas of SSA-100, SSA-300, and SSA-600 nanosilica (NSI) particles were quoted as 90–105 m2/g, 285–305 m2/g, and 580–610 m2/g, respectively, by Lu Ming Nanomaterials Corporation. Functionalized nanosilica (FNSI) particles were prepared by grafting maleic anhydride grafted polyethylene () molecules onto NSI particles in ultrasonicated mixtures of decalin, NSI, and at 170°C for 1 hour, in which, resin was purchased from Langfang Plastic Corporation, Langfang, China. The nanosilica and functionalized nanosilica particles prepared above are referred to as and , respectively, in the following discussion, in which, the superscript denotes the quoted specific surface areas of virgin NSI nanosilica particles and the subscript denotes the weight ratio of to used in the preparation processes of functionalized nanosilica particles. Table 1 summarized designations and compositions of typical nanosilica and functionalized nanosilica particles prepared in this study.


and specimensMass ratios of to Specific surface areas (m2/g)

NSI1000.0102.3
1.0109.7
2.0114.8
3.0129.8
6.0122.4
12.0109.6

NSI3000.0303.9
2.0314.5
3.0325.5
6.0335.8
9.0330.8
12.0315.3

NSI6000.0601.7
2.0617.4
3.0621.4
6.0625.3
9.0630.7
12.0621.4

Varying contents of and particles together with UHMWPE resin were dispersed and dissolved in decalin at 135°C for 1.5 hours, in which 0.1% di-t-butyl-p-cresol was added as an antioxidant. The UHMWPE, , and gel solutions prepared above were then fed into a temperature-controlled hopper and kept as hot homogenized gel solutions before spinning. The hot homogenized gel solutions were then gel-spun using a conical die with an exit diameter of 1 mm at an extrusion rate of 1000 mm/min and an extrusion temperature of 170°C. A water bath and a winder with 70 mm in diameter were placed at a distance of 520 mm and 810 mm from the spinneret exit, respectively. The extruded gel fibers were cooled in a temperature-conditioned atmosphere and then quenched into a water bath for about 1 minute, where the temperature of the air atmosphere and water bath was controlled at 5°C. The quenched fibers were then extracted in n-hexane bath for 5 minutes to remove the residual decalin solvent. The extracted fiber specimens were then dried in air for 30 minutes to remove the remaining n-hexane solvent before any drawing run. The UHMWPE, , and as-prepared fiber specimens prepared above are referred to as F100, , and as-prepared fiber specimens, respectively, in the following discussion, in which, the superscript denotes the quoted specific surface areas of varying particles used to prepare and particles in and as-prepared fiber specimens, respectively; the subscript 100 denotes one hundred parts of UHMWPE resins used in the as-prepared fibers; denotes the weight ratio of to used in the preparation processes of fillers, while the subscript denotes parts of or fillers used in per hundred parts of UHMWPE resins in the as-prepared fibers. Table 2 summarized designations of typical UHMWPE, UHMWPE/nanosilica, and UHMWPE/functionalized nanosilica as-prepared fiber specimens and the corresponding compositions of gel solutions used in the gel spinning processes.


As-prepared fiber specimensOriginal nanosilica (g/phr)Functionalized nanosilica (g/phr)UHMWPE
(g/phr)
Volumes of decalin in gel solutions (mL)
(°C)

(%)

(nm)

F10002/100100142.765.130.7
F1000.001/0.052/100100141.167.825.6
F1000.002/0.12/100100140.270.117.5
F1000.0025/0.1252/100100141.966.018.2
F1000.00075/0.03752/100100140.968.322.5
F1000.00125/0.06252/100100140.270.817.5
F1000.002/0.12/100100141.167.822.5
F1000.00075/0.03752/100100140.769.119.3
F1000.001/0.052/100100139.971.515.7
F1000.002/0.12/100100140.867.822.1
F1000.00075/0.03752/100100141.666.225.8
F1000.0015/0.0752/100100139.370.315.1
F1000.002/0.12/100100139.569.015.4
F1000.00075/0.03752/100100140.769.117.5
F1000.0015/0.0752/100100138.375.412.4
F1000.002/0.12/100100138.975.113.5
F1000.00075/0.03752/100100140.968.922.5
F1000.0015/0.0752/100100139.272.414.1
F1000.002/0.12/100100139.671.314.7
F1000.0005/0.0252/100100139.573.214.6
F1000.001/0.052/100100138.674.013.1
F1000.0015/0.0752/100100139.373.414.2
F1000.0005/0.0252/100100138.575.212.7
F1000.001/0.052/100100137.676.011.3
F1000.0015/0.0752/100100138.375.412.4
F1000.0005/0.0252/100100139.074.113.6
F1000.001/0.052/100100138.175.012.0
F1000.0015/0.0752/100100138.873.913.5
F1000.0005/0.0252/100100137.874.211.6
F1000.00075/0.03752/100100137.274.810.7
F1000.0015/0.0752/100100138.373.712.4
F1000.0005/0.0252/100100136.576.210.7
F1000.00075/0.03752/100100136.176.89.5
F1000.0015/0.0752/100100137.075.910.1
F1000.0005/0.0252/100100137.374.711.1
F1000.00075/0.03752/100100136.775.39.8
F1000.0015/0.0752/100100137.874.311.6

2.2. Fourier Transform Infrared Spectroscopy

Fourier transform infrared (FTIR) spectroscopic measurements of or specimens with varying specific surface areas were recorded on a Nicolet Avatar 360 FTIR spectrophotometer at 25°C, wherein 32 scans with a spectral resolution 1 cm−1 were collected during each spectroscopic measurement. Infrared spectra of or film specimens were determined using the conventional KBr disk method. Alcohol and decalin solutions containing or particles, respectively, were cast onto KBr disk and dried at 60°C for 30 minutes. The cast films used in this study were prepared sufficiently thin enough to obey the Beer-Lambert law.

2.3. Morphological Analyses

In order to understand the morphology on the surfaces of or particles with varying specific surface areas prepared in Materials and Sample Preparation, particles were dispersed in alcohol, while particles were dispersed in decalin to have a better dispersed morphology before examination. Before morphological analyses, ten micrograms of or particles was added and ultrasonicated in 10 mL alcohol and decalin at 25°C for 5 minutes, respectively. The dispersed particles were then dried onto a carbon-coated copper grid under ambient conditions prior to morphological analyses. The cast or particles were then examined using a Philip transmission electron microscope (TEM) model Tecnai G20 operated at 200 kV.

2.4. Specific Surface Area Analyses

A Laser Particle Size Analyzer model BT-9300H (Dandong Bettersize Instruments Corporation, Dandong, China) was used to study the specific surface areas of or particles with varying specific surface areas. Before analyses, ten micrograms of or particles was added and ultrasonicated in 10 mL alcohol and decalin at 25°C for 5 minutes, respectively. The specific surface areas of or particles were then measured by placing the ultrasonicated solutions prepared above in the curette of the Laser Particle Size Analyzer at 25°C.

2.5. Thermal and Orientation Factor Analyses

Thermal properties of all as-prepared fiber specimens were performed on a Du Pont differential scanning calorimeter (DSC) model 2000. All scans were carried out at a heating rate of 20°C/min under flowing nitrogen at a flow rate of 25 mL/min. Samples weighing 0.5 mg and 15 mg were placed in the standard aluminum sample pans for determination of their melting temperature () and percentage crystallinity () values, respectively. The percentage crystallinity values of the as-prepared fiber specimens were estimated using baselines drawn from 40 to 200°C and a perfect heat of fusion of polyethylene of 293 J/g [28].

In order to understand the ultradrawing properties of UHMWPE, , and as-prepared fiber specimens, the lamellar thickness () values of the above as-prepared fibers were evaluated from their values using Hoffman and Weeks’ equation [28, 29] given in (1) as follows, in which, an equilibrium melting temperature () of 145.5°C, a perfect heat of fusion () of 293 J/g, and a folded surface free energy () of 9 × 10−6 J/cm2 of polyethylene crystals [28] were used for evaluation of values of UHMWPE, UHMWPE/NSI, and UHMWPE/FNSI as-prepared fiber specimens:

The orientation factor () values of UHMWPE, , and as-prepared and drawn fiber specimens were measured using a sonic velocity orientation instrument model SCY-III, which was purchased from Donghuakaili Chemicals and Fiber Technology Corporation, Shanghai, China. Before testing, the fiber specimen with 60 cm in length was wound and clamped on a testing device with a span of 40 cm. values of the as-spun and drawn fiber specimens were then measured at 25°C. A minimum of five samples of each specimen were tested and averaged during measurements. values were evaluated using (2) as suggested by Xiao and coauthors [30]: where is the sonic velocity of the as-prepared or drawn UHMWPE fiber specimen and is the sonic velocity of the fully unoriented sample, taken as 1.65 km/s [30].

2.6. Drawing and Tensile Properties of Fiber Specimens

The UHMWPE, , and fiber specimens used in the drawing experiments were cut from the dried as-prepared fibers and then stretched on a Gotech tension testing machine model GT-TFS-2000 equipped with a temperature-controlled oven. The fibers are 150 mm in length, which were wound and clamped in a stretching device and then stretched at a crosshead speed of 20 mm/min and a constant temperature of 95°C. The draw ratio of each fiber specimen was determined as the ratio of the marked displacement after and before drawing. The marked displacement before drawing was 27 mm. The tensile properties of the as-prepared and drawn fibers were determined using a Hung Ta tension testing machine model HT-9112 at a crosshead speed of 20 mm/min. A minimum of five samples of each specimen were tested and averaged during the tensile experiments.

3. Results and Discussion

3.1. Fourier Transform Infrared Spectroscopy

Figure 1 illustrates typical Fourier transform infrared (FTIR) spectra of nanosilica (), functionalized nanosilica (), and maleic anhydride grafted polyethylene () specimens. specimen exhibited two distinctive absorption bands centered at 1711 and 1791 cm−1, which were generally attributed to the motion of O-C=O and C=O stretching vibrations of maleic anhydride [31] (see Figure 1(a)). As shown in Figures 1(b), 1(f), and 1(j), there are three distinguished absorption bands centered at 1097, 1635, and 3442 cm−1 corresponding to the motions of Si-O-Si stretching, H-O-H bending, and Si-OH stretching vibrations [31], respectively, which were found in the spectra of NSI100, NSI300, and NSI600 specimens. It is interesting to note that the peak magnitudes of Si-O-Si stretching, H-O-H bending, and Si-OH stretching bands of specimens increased significantly as their quoted specific surface areas increased from 100 to 300 and 600 m2/g (see Figures 1(b), 1(f), and 1(j)). The significant increase in the magnitude of Si-O-Si stretching, H-O-H bending, and Si-OH stretching bands of specimens is attributed to the increased amounts of Si-O-Si, H-O-H, and Si-OH groups exposed on particles with higher specific surface areas.

After grafting to NSI100, NSI300, and NSI600 particles, the peak magnitudes corresponding to H-O-H bending and Si-OH stretching bands of specimens reduced significantly as the weight ratios of to increased (see Figures 1(b) to 1(e), 1(f) to 1(i), and 1(j) to 1(m)). In fact, as shown in Figures 1(d) to 1(e), 1(h) to 1(i), and 1(l) to 1(m), H-O-H bending and Si-OH stretching bands originally present in specimens disappeared almost completely as the weight ratios of to NSI100, NSI300, and NSI600 of , , and specimens were equal to or more than 3, 6, and 9, respectively. In the meantime, a new absorption band centered at around 1228 cm−1 corresponding to the motion of ester C-O stretching vibration [31] was found in the spectra of , , and specimens (see Figures 1(c) to 1(e), 1(g) to 1(i), and 1(k) to 1(m)). In contrast, the absorption bands centered at 1711 and 1791 cm−1 corresponding to the motion of C=O and O-C=O stretching vibrations of maleic anhydride gradually reappeared as the weight ratios of to NSI100, NSI300, and NSI600 of , , and specimens, respectively, were equal to 6, 9, and 12. Presumably, the gradually disappearing H-O-H bending and Si-OH stretching bands and newly developed ester C-O stretching bands of , , and specimens are attributed to the reaction of the hydroxyl groups of NSI100, NSI300, and NSI600 particles with the maleic anhydride groups of molecules during their functionalized processes. The reappearance of O-C=O and C=O stretching bands of maleic anhydride groups is most likely due to the overdosage of during the functionalized processes of , , and particles.

3.2. Morphological Analyses of and Particles

Figure 2 exhibits typical TEM micrographs of and particles. Typical irregular particle feature with dimensions of 250–350, 150–200, and 50–80 nm in diameter was observed for NSI100, NSI300, and NSI600 particles (see Figures 2(a), 2(d), and 2(g)). After modification by , some translucent resins were found attaching on the surfaces of NSI100, NSI300, and NSI600 particles, wherein the amounts of attached translucent resins increased gradually as the weight ratios of to NSI100, NSI300, and NSI600 increased, respectively (see Figures 2(b) to 2(c), 2(e) to 2(g), and 2(h) to 2(i)). As evidenced by FTIR analyses in the previous section, the attached translucent resins were most likely the grafted molecules, which were firmly bonded to NSI100, NSI300, and NSI600 particles by the reaction of the maleic anhydride groups of resins with the hydroxyl groups of NSI100, NSI300, and NSI600 particles, respectively. In fact, the translucent resins were found fully surrounding and overwrapping on NSI100, NSI300, and NSI600 particles, as the weight ratios of to NSI100, NSI300, and NSI600 were greater than 3, 6, and 12, respectively (see Figures 2(c), 2(f), and 2(i)).

3.3. Specific Surface Area Analyses of and Particles

The values of specific surface areas of and particles are summarized in Figure 3 and Table 1. The specific surface areas of NSI100, NSI300, and NSI600 particles were evaluated at around 100, 300, and 600 m2/g (i.e., 102.3, 303.9, and 601.7 m2/g), respectively. After modification by , the specific surface areas of , , and particles reached a maximal value at 129.8, 335.8, and 630.7 m2/g, respectively, as the weight ratios of to NSI100, NSI300, and NSI600 approached an optimal value at 3, 6, and 9, respectively. Presumably, the beneficial effect of contents on specific surface areas of particles is attributed to the increase in grafted amounts and specific surface areas of on particles during their functionalized processes. However, molecules may agglomerate, bundle, entangle together, and overwrap particles, as molecules are superfluous and can no longer graft onto particles. As evidenced by morphology analyses in the previous section, some translucent resins were found fully surrounding and overwrapping on particles (see Figures 2(c), 2(g), and 2(i)), as the weight ratios of to NSI100, NSI300, and NSI600 were more than 3, 6, and 9, respectively. Based on this premise, it is reasonable to infer that the overwrapped particles exhibit relatively lower specific surface areas than those , , and particles grafted with proper amounts of resins.

3.4. Thermal Properties of the As-Prepared Fibers

Typical DSC thermograms, melting temperature (), percentage crystallinity (), and evaluated lamellar thickness () values of UHMWPE (F100), UHMWPE/NSI (), and UHMWPE/FNSI () as-prepared fiber series specimens are summarized in Figure 4 and Table 2. A main melting endotherm with and at 142.7°C and 65.1%, respectively, was found for F100 specimen. After incorporation of and/or particles in UHMWPE, (or evaluated ) values of (i.e., , , and ) and/or (i.e., , , and ) as-prepared fibers reduced to a minimal value, as their and/or contents reached an optimal value, respectively, in which and values of , , and as-prepared fibers prepared at the optimal contents at 0.075, 0.05, and 0.0375 phr, respectively, were significantly lower than those of the corresponding , , and as-prepared fibers with an optimal content at 0.1, 0.0625, and 0.05 phr, respectively. However, values of and/or as-prepared fibers increased to a maximal value, as and/or contents reached their corresponding optimal values, respectively, wherein values of , , and as-prepared fibers prepared at their optimal contents, respectively, were significantly higher than those of the corresponding , , and as-prepared fibers prepared at their optimal contents, respectively. Moreover, it is worth noting that , , and as-prepared fibers prepared at the optimal contents exhibited another minimal (or evaluated ) but other maximal values as their , , and were modified using an optimal weight ratio of to NSI100, NSI300, and NSI600 at 3, 6, and 9, respectively (see Figures 5(j), 6(i), and 7(h)). Finally, it is interesting to note that the lowest (or evaluated ) values obtained for , , and as-prepared fibers prepared at the optimal contents and weight ratio of to reduced significantly as the specific surface areas of particles increased, while the highest values obtained for , , and as-prepared fibers increased consistently as the specific surface areas of their particles increased. For instance, values of , , and as-prepared fibers reduced from 138.3°C to 137.6°C and to 136.1°C, as the specific surface areas of , , and present in , , and as-prepared fibers increased from 129.8 to 335.8 and 630.7 m2/g, respectively, while their values increased from 75.4% to 76.0% and 76.8%, as the specific surface areas of , , and present in , , and as-prepared fibers increased from 129.8 to 335.8 and 630.7 m2/g, respectively.

As evidenced by specific surface area and TEM analyses in the previous sections, and/or particles are with a wide range of relatively large surface areas per volume, which make them in close proximity to a large fraction of the UHMWPE matrix. Apparently, even very small contents of dispersed and/or particles can serve as efficient nucleation sites for UHMWPE molecules during their gel spinning processes. These efficient nucleation sites of and/or particles then facilitate the crystallization of UHMWPE molecules into crystals with thinner lamellar thickness and/or lower values during their crystallization processes. After grafting to NSI100, NSI300, and NSI600 particles, the properly modified particles with even higher specific surface areas are likely to disperse better in UHMWPE and serve as more effective sites for nucleation of UHMWPE molecules during their gel spinning processes than particles. As a consequence, , , and as-prepared fiber specimens exhibit significantly higher but lower (or evaluated ) values than the corresponding , , and as-prepared fiber specimens prepared with the same contents but without modification by , respectively. Moreover, the minimal (or evaluated ) values obtained for , , and as-prepared fibers prepared at the optimal contents and weight ratio of to , respectively, reduced significantly as the specific surface areas of particles increased, while the highest values obtained for , , and as-prepared fibers increased consistently as the specific surface areas of their particles increased.

3.5. Achievable Draw Ratios of the As-Prepared Fibers

Figure 5 summarized the achievable draw ratio (achievable ) values of F100, , and as-prepared fiber specimens prepared at varying and/or contents, respectively. For comparison purposes, achievable values of the best prepared UHMWPE/functionalized carbon nanotube (FCNT) as-prepared fibers (i.e., specimens) obtained in our previous investigations [24] were also summarized in Figure 5, in which, functionalized carbon nanotubes are with relatively high (i.e., 272.7 m2/g) but significantly lower specific surface areas than those of and particles prepared in this study. After addition with and/or particles in UHMWPE, the achievable values of and/or as-prepared fibers increased initially and reached a maximal value as their and/or contents approached an optimal value, respectively, in which the achievable values of , , and as-prepared fibers prepared at the optimal contents at 0.075, 0.05, and 0.0375 phr, respectively, were significantly higher than those of the corresponding , , and as-prepared fibers prepared at the optimal contents at 0.1, 0.0625, and 0.05 phr, respectively. Moreover, it is worth noting that , , and as-prepared fibers prepared at the optimal contents exhibited other maximal achievable values at 176, 289, and 361, respectively, as their , , and particles were modified using an optimal weight ratio of to NSI100, NSI300, and NSI600 at 3, 6, and 9, respectively. It is further interesting to note that the highest achievable values obtained for the best prepared , , and as-prepared fibers prepared at the optimal contents and weight ratios of to improved significantly as the specific surface areas of their particles increased. In fact, the maximal achievable value (i.e., 361) obtained for as-prepared fiber is about 2.05 and 1.25 times of those of and the best prepared UHMWPE/FCNT as-prepared fibers and is 2.85 times of that of F100 as-prepared fiber without addition of original and/or modified nanosilica particles.

3.6. Orientation Factor Analyses of the As-Prepared and Drawn Fiber Specimens

Typical orientation factor () values of F100, , and as-prepared and drawn fibers are summarized in Figure 6. No significant difference in values was found for F100, , and as-prepared fibers. As expected, values of F100, , and fibers increased consistently as their draw ratios increased. After addition of and/or particles, values of drawn and/or fibers were significantly higher than those of drawn F100 fibers with the same draw ratios. values of drawn fibers with a fixed draw ratio reached a maximal value as their NSI100, NSI300, and NSI600 contents approached the optimal values at 0.1, 0.0625, and 0.05 phr, respectively. Similarly, values of each drawn fiber series specimen reached a maximal value as their , , and contents approached an optimal value at 0.075, 0.05, and 0.0375 phr, respectively, in which, values of drawn , , and fibers prepared at the optimal contents were significantly higher than those of the corresponding drawn , , and