Weld lines in nylon 6 melt-blended nanocomposites.INTRODUCTION
In recent years, layered silicate silicate, chemical compound containing silicon, oxygen, and one or more metals, e.g., aluminum, barium, beryllium, calcium, iron, magnesium, manganese, potassium, sodium, or zirconium. Silicates may be considered chemically as salts of the various silicic acids. nanocomposites have attracted a great deal of interest from researchers, being a new class of composite that contain nanoparticles dispersed in a polymer matrix . Nylon 6 nanocomposites are usually comprised of montmorillonite-containing silicate layers that are ~1 nm in thickness and are preferably fully delaminated and uniformly dispersed within the polymer matrix . Nylon 6 organoclay nanocomposites can be produced by either melt blending, in situ In place. When something is "in situ," it is in its original location. polymerization polymerization
Any process in which monomers combine chemically to produce a polymer. The monomer molecules—which in the polymer usually number from at least 100 to many thousands—may or may not all be the same. , or solution  mixing techniques. Melt blending is the most common method for preparing nylon 6 nanocomposites, with the organoclay directly mixed with the molten polymer. The melt blending technique is economical and straightforward, and while maximum exfoliation exfoliation /ex·fo·li·a·tion/ (eks-fo?le-a´shun)
1. a falling off in scales or layers.
2. the removal of scales or flakes from the surface of the skin.
3. of organoclay is not usually achieved, such a combination with nylon 6 produces a relatively high level of delamination delamination /de·lam·i·na·tion/ (de-lam?i-na´shun) separation into layers, as of the blastoderm.
1. A splitting or separation into layers.
The injection molding injection molding
A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold. process involves the injection of a polymer melt flow into a cavity mold where the melt cools and solidifies to form a plastic product and is a three-phase process comprising filling, packing, and cooling phases. Weld lines are a source of mechanical weakness and their formation is an unavoidable defect in injection molding due to the complexity of modern product design. The formation of weld lines inevitably occurs when there are cores, pins, and multiple gates, all of which divide the molten polymer flow pattern in the cavity mold. While weld lines can be deleterious in homopolymer moldings, the problem can be amplified in two-phase systems, such as glass-reinforced thermoplastics .
Weld lines also consist of v-notches at the weld line surface, which is often forgotten as one of the possible causes of weakening, potentially acting as stress concentrators by increasing the stress level at the bottom of a v-notch . Chang and Faison  reported that v-notch appearance and weld line locations depend on the design of mold and product, and subsequently processing conditions. The appearance of weld lines is found to be more visible on one surface than the other of the molding. Using optical microscopy, fan-shaped v-notches are noticeable at the edges of the weld lines. It was reported that the fan-shaped appearance is caused by the polymer melt fronts impinging at the weld region . The different appearance of both sides of the specimen is attributed to the geometry of the specimen and the location of the mold parting line, through which air escapes from the advancing melt fronts.
A number of remedies for controlling processing conditions have been investigated in order to enhance the molecular diffusion at the weld line boundaries in injection-molded products . The most significant processing parameters that have been identified in polymers such as polystyrene, polypropylene, polycarbonate A category of plastic materials used to make a myriad of products, including CDs and CD-ROMs. , and polyoxymethylene (POM) are, in decreasing order of importance: melt temperature, mold temperature, holding pressure, holding time, and injection velocity. Temperature was found to be the dominant factor influencing the weld line strength. Liu et al.  investigated the temperature corresponding to the healing ability of a material at the weld line by determining the level of molecular entanglement after different temperature and time treatments. As expected, the chain segments have an increased ability to flow and knit when there is sufficient temperature and time.
The purpose of this study was to investigate weld line behavior in injection-molded tensile specimens of nylon 6 nanocomposite containing organically modified montmorillonite Montmorillonite is a very soft phyllosilicate mineral that typically forms in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a (organoclay), which was produced by the melt blending technique. Nylon 6 nanocomposites consist of extremely thin and high surface area, nanometer-scale dispersions of layered silicates. The low loading weight of organoclay is expected to achieve high stiffness and strength due to their potentially high aspect ratio (e.g., 50-500) and the unique intercalation/exfoliation characteristics of silicate platelets in nylon 6 nanocomposite. Nylon 6 nanocomposites containing only 4 wt% of well-exfoliated silicate layers can yield mechanical properties comparable to a 20 wt% mica-filled nylon 6 composite .
Neat nylon 6 is used as the control material to highlight the effect of organoclay in the polymer matrix. In addition, the work will identify the principal process factors important for nylon 6 nanocomposites when a weld line is present. It has also been reported that the decrease in mechanical properties for weld lines containing conventional fillers is due to the fillers aligning perpendicular to the flow direction at the weld line . This work seeks to determine whether the flow orientation of organoclay and matrix morphology similarly influences mechanical properties in the weld region. Single-end-gated samples were also made to determine the effect of the presence of a weld line in the tensile specimens. The Taguchi experimental design approach is used in this study to help identify the most important influences on weld line strength because it provides significant information from relatively few experimental runs . A modified [L.sub.16] orthogonal array was designed, according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. the experimental-parameter-design method previously developed [12, 13]. The signal-to-noise (S/N (1) (Serial/Number) Common shorthand for serial number.
(2) (Signal/Noise) As in "s/n ratio." See signal-to-noise ratio. ) ratio, a sensitivity test proposed by Liu et al.  and Turng and Kharbas , was also used to identify the principal process factors and the optimum molding conditions, while an analysis of variance (ANOVA anova
see analysis of variance.
ANOVA Analysis of variance, see there ) was used to evaluate the effect of the various process factors on weld strength in an orderly sequence . Failure surfaces from the tensile tests were investigated to understand the influence of the resulting polymer morphology on tensile properties.
Neat nylon 6 and nylon 6 nanocomposite were obtained from RTP (1) (Rapid Transport Protocol) The protocol used in IBM's High Performance Routing (HPR) system.
(2) (Realtime Transport Protocol) An IP protocol that supports real time transmission of voice and video. (Winona, MN). Both materials have an average molecular weight, Mn, of 18,000. The nylon 6 nanocomposite containing organically modified montmorillonite (organoclay) was produced by the supplier by a melt blending technique.
[FIGURE 1 OMITTED]
Thermogravimetric Analysis Thermogravimetric Analysis or TGA is a type of testing that is performed on samples to determine changes in weight in relation to change in temperature. Such analysis relies on a high degree of precision in three measurements: weight, temperature, and temperature change.
The precise weight of inorganic clay content in the commercial nylon 6 nanocomposites was measured using a thermogravimetric analysis (TGA See TARGA.
TGA - Targa Graphics Adaptor ), Setaram TG92 at a heating rate of 30K/min from 50-1000[degrees]C in an argon argon (är`gŏn) [Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C;; b.p. −185.7°C;; density 1.784 grams per liter at STP; valence 0. gas flow.
Injection-molded specimens of the materials were injected with a Battenfeld (South Elgin, IL) model Plus 350-75 35ton injection molding machine Injection molding machine (also known as injection press) - a machine for making plastic parts. Manufacturing products by injection molding process. Consist of two main parts, an injection unit and a clamping unit. (screw diameter = 30 mm, L/D L/D Labor and Delivery
L/D Lethal Dose
L/D Lift/Drag (ratio)
L/D Low Dynamic
L/D Loading / Discharging Rate (shipping) ratio = 13.5:1, maximum injection pressure = 109.4 MPa) along with a Yann Bang (Taiwan) model YBM-I-P mold temperature controller.
Dumbbell-shape tensile specimens of double-end-gated cavities were used in this study (see Fig. 1). In single-end-gated specimens, there are no weld lines present and they are referred to as single-end-gated samples, while in double-end-gated specimens a weld line is formed at the middle of the tensile bar and it is referred to as a double-end-gated sample.
A modified [L.sub.16] orthogonal array with three levels (except back pressure) was used to schedule the injection molding experiments  (Table 1). Eight different process factors were evaluated, namely, injection pressure, holding pressure, holding time, back pressure, screw rotational speed Rotational speed (sometimes called speed of revolution) indicates, for example, how fast a motor is running. Rotational speed is equivalent to angular speed, but with different units. Rotational speed tells how many complete rotations (i.e. , melt temperature, mold temperature, and cooling time (Law) such a lapse of time as ought, taking all the circumstances of the case in view, to produce a subsiding of passion previously provoked.
See also: Cooling . Several injection trials were conducted to obtain upper and lower parameter setting conditions prior to the main experiments to ensure reproducibility in sample quality. These conditions then served as a guide to preset various processing parameters for further experiments (Table 2).
Tensile testing was conducted after 1 week of storage of the molded tensile specimens to allow equilibration equilibration /equi·li·bra·tion/ (e-kwil?i-bra´shun) the achievement of a balance between opposing elements or forces.
occlusal equilibration under atmospheric conditions. Tensile properties were measured according to ASTM ASTM
American Society for Testing and Materials D638-87b using an Instron (Norwood, MA) 4505 with a 5kN load cell and a crosshead cross·head
A beam that connects the piston rod to the connecting rod of a reciprocating engine.
Noun 1. crosshead - a heading of a subsection printed within the body of the text
crossheading speed of 50 mm/min. The ultimate tensile strength tensile strength
Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its of single-end-gated samples is referred to as bulk strength, while the failure strength of double-end-gated samples with weld lines will be called weld strength.
Optical Microscopy and Environmental Scanning Electron Microscopy electron microscopy
Technique that allows examination of samples too small to be seen with a light microscope. Electron beams have much smaller wavelengths than visible light and hence higher resolving power.
The weld line of double-end-gated tensile specimens was observed by reflection optical microscopy using an Olympus (Lake Success, NY) model PMG PMG
1. Postmaster General
2. Paymaster General 3. Fracture surfaces of tensile failure specimens were examined on an environmental scanning electron microscope scan·ning electron microscope
n. Abbr. SEM
An electron microscope that forms a three-dimensional image on a cathode-ray tube by moving a beam of focused electrons across an object and reading both the electrons scattered by the object and (ESEM ESEM Environmental Scanning Electron Microscope
ESEM International Symposium on Empirical Software Engineering and Measurement
ESEM Experiment of Space Environment with Materials
ESEM Ethernet Service Expansion Module ), FEI FEI
Fédération Équestre Internationale. model Quanta quan·ta
Plural of quantum. 200 at low vacuum, 20 kV under a back-scattering condition.
RESULTS AND DISCUSSION
Thermogravimetric Analysis (TGA)
The thermogravimetric analysis results show that the inorganic clay content of the nylon 6 nanocomposite is 3.5 [+ or -] 0.5 wt%. Since this material is obtained commercially, the precise type and amount of organoclay surface treatment (layered silicate and organo-ion) is unknown, but it often amounts to ~30 wt% organo-ion in most commercial samples. It is likely that between 4 and 5 wt% of organoclay was blended with the nylon to form the nanocomposite.
Comparison of Nylon 6 and Nylon 6 Nanocomposites
Figures 2 and 3 show the tensile stress-strain curves for neat nylon 6 and the nylon 6 nanocomposite. The tensile specimens were injection-molded under standard processing conditions. Table 3 summarizes the ultimate tensile strength and strain-to-failure for the neat nylon 6 and the nanocomposite, both with and without weld lines. The clear difference is that the weld line in the nanocomposite is weaker than the single-end-gated samples, whereas in the neat nylon the strength is not significantly affected.
[FIGURE 2 OMITTED]
Figure 2 demonstrates that the neat nylon 6 is tough and ductile ductile /duc·tile/ (duk´til) susceptible of being drawn out without breaking.
Easily molded or shaped.
susceptible of being drawn out without breaking. , even with a weld line present, and that the presence of a weld line causes little variation in tensile properties. The double-end-gated sample does not fail at the weld region but rather randomly along the gauge length of the tensile bar specimens. Clearly, the interdiffusion of the polymer molecules at the weld region is extensive for the neat nylon 6, and the weld line defect is visually observed with difficulty on the tensile specimen. Both the single- and double-end-gated samples of neat nylon cold-draw under a uniaxial tensile force, and elongate e·lon·gate
tr. & intr.v. e·lon·gat·ed, e·lon·gat·ing, e·lon·gates
To make or grow longer.
adj. or elongated
1. Made longer; extended.
2. Having more length than width; slender. to a significant strain (greater than 132%) before failure.
Figure 3 shows that the nylon 6 nanocomposite exhibits rigid and brittle behavior, even without a weld line present. The brittleness of the nylon 6 nanocomposite demonstrates that even a low loading of organoclay in the nylon, i.e., 4-5 wt%, is able to influence the mechanical properties significantly. Clearly, the inherent size of the organoclay plays a dominant role in the property performance. The double-end-gated samples with weld lines have even lower tensile strength and strain-to-failure compared to the single-end-gated samples. A surface notch is observed at the weld line of the double-end-gated samples, due to air being entrapped at the weld line interface between the two opposing flow fronts. When the flow fronts impinge at the weld line, the entrapped hot air will also generate local heating and could cause some polymer degradation Polymer degradation is a change in the properties - tensile strength, colour, shape, etc - of a polymer or polymer based product under the influence of one or more environmental factors such as heat, light or chemicals. at the weld line and lead to the poor weld strength. The notch present at the weld line of the nylon 6 nanocomposite (Fig. 4a), which was estimated to be about 60 [micro]m in depth, could also act as stress concentrator and initiate crack propagation. A fan-shaped appearance of the notch can also be seen at the weld line edges. This differs from the neat nylon 6, where the notch was not observable in the double-end-gated samples (Fig. 4b), although the point of joining of the flow fronts was still observable as a line in the photograph. The greater notch depth in the nylon 6 nanocomposite may also illustrate the fact that the nylon nanocomposite exhibits a higher viscosity and melt strength, as both the neat nylon 6 and nylon 6 nanocomposite materials were processed under similar conditions in this work.
[FIGURE 3 OMITTED]
In addition to surface notch formation, the low nanocomposite weld strength could also be caused by organoclay agglomeration ag·glom·er·a·tion
1. The act or process of gathering into a mass.
2. A confused or jumbled mass: , where the organoclay is oriented and located at the weld line and acts as a stress concentrator, causing weakening (see Fig. 5). This is clearly different from the neat nylon 6, which has no nanoparticles in the polymer matrix. Examination of the tensile fracture surfaces of nanocomposite samples shows that the double-end-gated tensile specimens (which invariably in·var·i·a·ble
Not changing or subject to change; constant.
in·vari·a·bil failed in the weld region) leave a smoother fracture surface (Fig. 6a) than the single-end-gated samples (Fig. 6b). Organoclay orientation in a high shear flow Shear flow is:-
[FIGURE 4 OMITTED]
The planar orientation of nanoparticles may also hinder molecular chain motion on solidification and inhibit optimal crystalline development and orientation in the weld line region. Indeed, it is also well known that incorporation of organoclay in nylon 6 can enhance the [gamma]-phase crystal structure compared to the [alpha]-phase crystalline phase of neat nylon 6, which may itself affect the physical and mechanical properties . It was found that the organoclay enhances the [gamma]-phase crystal structure from ~2% (neat nylon 6) to ~30% (nylon 6 nanocomposite), while maintaining [alpha]-phase crystal structure at between 25% and 50% in nylon 6 nanocomposite .
Further possible explanations for the poor weld strength of the nylon 6 nanocomposite could be that higher moisture absorption is likely at the weld line area of the samples following solidification and before testing. Nylon is a hygroscopic hygroscopic /hy·gro·scop·ic/ (hi?gro-skop´ik) readily absorbing moisture.
Readily absorbing moisture, as from the atmosphere. material due to the polar amide groups. The planar orientation of the nanoparticles provides additional surface area and possibly voids in the weld line region, thus encouraging the weld region to absorb moisture at a rate faster than for the rest of the molded part, a similar effect having been noted for glass fiber-filled nylon .
Because of this particular sensitivity of the tensile strength to weld lines, the following investigation was undertaken to determine the processing conditions under which the nanocomposite material could be processed to minimize the weld line effect.
Principal Process Factors Determination
The significance of the effect of the processing factors can be evaluated using an S/N ratio S/N ratio - signal-to-noise ratio and (ANOVA). Both the S/N ratio and ANOVA use data from measurements of the ultimate tensile strength of the injection molding.
S/N ratio. In this section the S/N ratio is used to determine the degree of response due to variations of each parameter under consideration. It is used to evaluate the significance of process factors in determining the ultimate tensile strength, and to determine an optimum molding condition that achieves the highest tensile strength. The S/N ratio formulation is:
[S/N] ratio = -10 [log.sub.10]([1/n] [n.summation summation n. the final argument of an attorney at the close of a trial in which he/she attempts to convince the judge and/or jury of the virtues of the client's case. (See: closing argument) over (i=1)] [1/[y.sub.i.sup.2]]),
where n is the number of specimens tested in each run and [y.sub.i] is the measured ultimate tensile strength.
Figure 7 shows the effect of the various process factors on the ultimate tensile strength of single- and double-end-gated samples of the nylon 6 nanocomposite. The results show that the injection pressure ([DELTA]S/N = 1.6) and mold temperature ([DELTA]S/N = 1.3) are the principal process factors for the single-end-gated samples, while the mold temperature ([DELTA]S/N = 1.3) and melt temperature ([DELTA]S/N = 1.1) are the most significant process factors for the double-end-gated samples.
As expected, the mold temperature has a profound effect on the bulk and weld strengths. Malguarnera and Manisali  investigated the effect of melt temperature, mold temperature, injection speed, and injection pressure on the tensile properties of polypropylene. They also found that increasing the mold temperature increased the ultimate tensile strength of both the single- and double-end-gated samples in polypropylene. The effect of mold temperature may be explained by considering that when the polymer melt begins to enter the cavity, it starts to lose heat as it contacts the cool mold, and relatively cool flow fronts impinge at the weld lines, reducing molecular interdiffusion across the polymer-polymer interface. A high mold temperature prolongs the molten state of the polymer melt during the injection stage, enabling the melt to more easily fill the rest of the cavity, generally increasing the bulk strength, as well as the weld strength. High weld strength is thus enhanced in the double-end-gated samples if the melt temperature remains sufficiently high for a long enough period of time to allow the molecular chain segments of the opposing flows to become entangled en·tan·gle
tr.v. en·tan·gled, en·tan·gling, en·tan·gles
1. To twist together or entwine into a confusing mass; snarl.
2. To complicate; confuse.
3. To involve in or as if in a tangle. , particularly when considering the effect of the possible planar orientation of nanoparticles at the weld line interface, which may inhibit such cross-diffusion .
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
The injection pressure plays a significant role in determining the bulk strength of the single-end-gated sample, but not so in the double-end-gated samples. The mold temperature has one of the highest S/N ratios for both single- and double-end-gated samples, indicating the importance of this temperature in achieving microstructures with high strength. This is underlined by the finding that for the double-end-gated samples the melt temperature is the second most important process variable, while for the single-end-gated samples melt temperature is important to a lesser degree than injection pressure. The apparent increased importance of injection pressure for the single-gated samples is probably due to the fact that the strength of the nonweld line-containing samples is essentially dependent on the microstructure mi·cro·struc·ture
The structure of an organism or object as revealed through microscopic examination.
a structure on a microscopic scale, such as that of a metal or a cell obtained along the entire gauge length, whereas the weld line-containing samples are critically dependent on the microstructure at the weld line itself, with diffusion across the weld line being of paramount importance. The injection pressure affects injection velocity, and thus shear rates and crystalline orientation, and so the strength. Such a phenomenon is less important in the double-end-gated samples where weld line behavior dominates strength.
[FIGURE 7 OMITTED]
Table 4 shows the optimum molding condition for single- and double-end-gated samples. This optimum molding condition is based on the maximum tensile strength achieved as a function of parameter setting. The results were derived from the various levels of process conditions listed in Tables 1 and 2. It can be seen that the single-end-gated molding condition is slightly different than for the double-end-gated molding configuration. The optimum molding condition for the double-end-gated configuration is achieved at a higher melt temperature, but at a lower injection pressure than for the single-end-gated configuration. This reinforces the observation that increased melt temperature enhances weld line strength due to molecular diffusion and entanglement at high temperatures [20, 21]. The reason for slightly lower injection pressures in the case of weld lines may be due to the levels of molded-in-stress building up at the melt fronts. The double-end-gated sample has a shorter maximum flow length, compared to the single-end-gated sample with the shorter flow length requiring lower injection pressures. High injection pressure at shorter flow length may lead to higher molded-in-stresses, particularly at the weld line where melt fronts impinge on each other. Thus, the double-end-gated sample prefers a lower injection pressure to achieve higher weld strengths.
ANOVA. Table 5 shows the ANOVA results calculated from the ultimate tensile strength data. The variance ratio (denoted F) is the ratio of a given factors mean to its mean square error . The F value shows the importance of the process factor in influencing the process response . A (relatively) large F value means the effect of the particular process factor is large, compared to the error variance. The significance of each process factor on the weld strength of injection-molded parts can therefore be judged by the F value. The calculated results show that the various process factors, in decreasing order of importance in affecting weld strength, are: mold temperature (18.1), melt temperature (12.8), back pressure (3.7), holding time (3.5), screw rotational speed (2.5), injection pressure (2.0), holding pressure (1.6), and cooling time (0.4). The mold temperature has the highest F value, meaning that this processing factor has the highest influence on the average weld strength and causes the greatest property change, while the cooling time has the lowest F value, and plays only a small role in enhancing weld strength.
This work is the first report of weld line behavior in nanocomposites. Neat nylon 6 shows little variation in tensile properties in the presence or absence of weld lines. Conversely, nylon 6 nanocomposites formed by melt-blending show higher tensile strengths, but much lower strain-to-failure, when compared with neat nylon 6. The strain-to-failure of neat nylon 6 retains a much higher value than the nylon 6 nanocomposite, even for double-end-gated samples. Clearly, in neat nylon 6 the molecules knit strongly across the weld line, while the inclusion of a low concentration of organoclay has a significant effect on the tensile properties. The organoclay increases the tensile strength, but adversely reduces the strain-to-failure. This may be due to the presence of notches at the weld line region, interference with the molecular diffusion across the boundary, or as a result of variation in orientation or type of crystallinity due to clay platelets.
An experimental design based on the Taguchi approach was used to identify the effect of the various process factors on the molding of nylon 6 nanocomposite. The modified [L.sub.16] orthogonal array with three levels is a simplified experimental design, and by running 16 experiments it allowed identification of the principal process factors and the optimum molding conditions for either single or double-end-gated samples. The ANOVA calculated results show the significance of the process factors on the double-end-gated samples, and so the effects on weld strength in decreasing order of importance are: mold temperature, melt temperature, back pressure, holding time, screw rotational speed, injection pressure, holding pressure, and cooling time. Current work is investigating the nature of crystalline and organoclay morphology at the weld line by a range of characterization techniques.
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J. Tung, G.P. Simon, G.H. Edward
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Correspondence to: J. Tung, e-mail: email@example.com
Contract grant sponsor: Cooperative Research Centre Cooperative Research Centres (CRCs) are key bodies for Australian scientific research. The Cooperative Research Centres Programme was established in 1990 to enhance Australia's industrial, commercial and economic growth through the development of sustained, user-driven, cooperative for Polymers (CRC-P).
TABLE 1. Modified [L.sub.16] orthogonal array an experimental design. A B C D Back Run no. Injection pressure Holding pressure Holding time pressure 1 A1 B2 C2 D1 2 A2 B2 C2 D1 3 A3 B2 C2 D1 4 A2 B1 C2 D1 5 A2 B3 C2 D1 6 A2 B2 C1 D1 7 A2 B2 C3 D1 8 A2 B2 C2 D2 9 A2 B2 C2 D1 10 A2 B2 C2 D1 11 A2 B2 C2 D1 12 A2 B2 C2 D1 13 A2 B2 C2 D1 14 A2 B2 C2 D1 15 A2 B2 C2 D1 16 A2 B2 C2 D1 E F G H Run no. Screw speed Melt temp. Mold temp. Cooling time 1 E2 F1 G3 H2 2 E2 F1 G3 H2 3 E2 F1 G3 H2 4 E2 F1 G3 H2 5 E2 F1 G3 H2 6 E2 F1 G3 H2 7 E2 F1 G3 H2 8 E2 F1 G3 H2 9 E1 F1 G3 H2 10 E3 F1 G3 H2 11 E2 F2 G3 H2 12 E2 F3 G3 H2 13 E2 F1 G1 H2 14 E2 F1 G2 H2 15 E2 F1 G3 H1 16 E2 F1 G3 H3 Key to symbols is in Table 2. TABLE 2. Parameter settings for the experimental design. Parameter setting Process factor Unit Symbol Level 1 Level 2 Level 3 Injection pressure MPa A 19 25 31 Holding pressure MPa B 19 22 25 Holding time s C 15 20 25 Back pressure MPa D 9 16 -- Screw rotational speed rpm E 30 55 70 Melt temperature [degrees]C F 268 280 290 Mold temperature [degrees]C G 40 60 80 Cooling time s H 20 30 40 TABLE 3. Tensile properties of nylon 6 and its nanocomposite, with and without weld lines. Ultimate tensile Material Sample strength Strain-to-failure Nylon 6 Single 51.4 MPa [+ or -] 5.0 135.7 [+ or -] 10.0% Double 50.9 MPa [+ or -] 7.0 132.2 [+ or -] 15.0% Nylon 6 Single 73.6 MPa [+ or -] 5.0 4.1 [+ or -] 0.3% Nanocomposite Double 52.7 MPa [+ or -] 5.0 3.2 [+ or -] 0.3% TABLE 4. Optimum molding condition achieved for single and double end-gated samples. Optimum condition Process factor Unit Symbol Single Double Injection pressure MPa A 31 19 Holding pressure MPa B 25 25 Holding time s C 25 25 Back pressure MPa D 16 16 Screw rotational speed rpm E 70 70 Melt temperature [degrees]C F 280 290 Mold temperature [degrees]C G 60 60 Cooling time s H 20 20 TABLE 5. Weld strength and ANOVA calculated results for nylon 6 nanocomposite produced as double end-gated samples. ANOVA Process Weld strength (Mpa) Sum of Degree of factor Level Run no. #1 #2 #3 #4 square freedom Injection 1 1 60.2 62.1 56.3 59.5 54.2 2 2 2 53.2 55.1 52.2 57.0 3 3 60.9 48.5 59.5 56.3 Holding 1 4 63.2 62.0 49.3 61.1 56.4 2 2 2 53.2 55.1 52.2 57.0 3 5 60.4 59.0 61.8 55.3 Holding 1 6 57.4 53.4 58.6 60.0 58.2 2 2 2 53.2 55.1 52.2 57.0 3 7 55.2 58.8 63.3 61.9 Back 1 2 53.2 55.1 52.2 57.0 63.1 1 2 8 52.0 61.9 62.5 63.6 Screw 1 9 50.7 61.7 65.0 65.4 89.4 2 2 2 53.2 55.1 52.2 57.0 3 10 60.4 58.7 60.8 58.2 Melt 1 2 53.2 55.1 52.2 57.0 110.9 2 2 11 58.9 61.2 57.5 58.8 3 12 62.0 65.0 59.0 61.1 Mold 1 13 59.6 59.4 56.7 57.0 157.7 2 2 14 64.8 60.0 65.5 62.7 3 2 53.2 55.1 52.2 57.0 Cooling 1 15 15.1 55.1 57.5 61.1 8.4 2 2 2 53.2 55.1 52.2 57.0 3 16 52.8 60.1 54.8 56.9 ANOVA Process Mean sum of Mean sum of factor Level square (factor) square (error) F value Injection 1 27.1 13.7 2.0 2 3 Holding 1 28.2 18.0 1.6 2 3 Holding 1 29.1 8.4 3.5 2 3 Back 1 63.1 16.9 3.7 2 Screw 1 44.7 17.9 2.5 2 3 Melt 1 55.4 4.3 12.8 2 3 Mold 1 78.9 4.4 18.1 2 3 Cooling 1 4.2 10.7 0.4 2 3