Tensile behaviour of adhesive overlap joints with PP, UHMW-PE … · 2017. 1. 29. · bonding of...

BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX

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Tensile behaviour of adhesive overlap joints with PP, UHMW-PE and PTFE polymers

R. Keresztes1, Z. Szakál2, A. Kári-Horváth2, T. Pataki2, Á. Sarankó3

Abstract: Polyolefines and PTFE are considered to be “difficult-to-bond” polymers. As a part of abroad research on virgin and plasma modified polymer surfaces, PP, UHMWPE, HD1000, HD500 and furthermore PTFE adhesion testing was performed. For that one and two-component different industrial structural bonding adhesives were used. The power of gluing was controlled by tensile tests in accordance with ISO 527 and DIN 1465 standard specimen requirements. In this work the virgin surface results are shown. He obtained results are good references for the further surface plasma treated polymer measurements. Beside the ranking of the bonding strength we paid attention to the typical failure process during the tensile tests and categorized each measurements concerning the type of failure. Keywords: adhesion bonding, adhesive, fluoropolymer, polymer, PP, UHMW-PE, PTFE, 1 INTRODUCTION The use of polymers expands rapidly in the technical practice. The gluing technology connected with polymers [3, 4, 7, 12, 14, 15] and its test [7, 17] tries keeping pace with this development. One of the main motivators of this is the vehicle industry, where the forming quick high-strength and elastic component contacts have got crucial importance. Here during production (sticking body and casing elements) and repairing (broken plastics, the bonding of windscreens) structural adhesives are used equally [1, 5]. Due to this currently not only the development of polymer composites is going on, but the market of the bonding materials was transformed in the past 5-10 years totally. New and newer adhesives appear with additional surface treatment materials, which help the adhesion of cements and the increase of their strength. We planned an overall experiment series, with the use of the most used engineering polymers and the new adhesion materials, with adhesives applied widespread in the industry in our present research. The adhesive substances are recommendation by Henkel Magyarország Ltd., we chose it from a product line of Loctite. The choice of the superglue and commonly-used one expand on structural adhesives, these are acrylic bases, and in the case of the superglues cyanoacrylate types [9]. We had it in our sight at the examination of engineering polymers qualified previously not at all bonding or as bonding hardly like polyolefin [6, 8], and the fluorine polymers [16]. Present article reports on the results of gluing experiments made with plain polymer on a surface without the special surface treatment. We carried out according to the ISO 527-1 standard the shear test of lap

joint made by the DIN EN 1465 standard with tensile-test machine. In the literature all the polyolefin [10, 21], all the fluorine [18, 19, 20] polymer basis articles, which added a footing to our examinations, are attached to the adhesive and mechanics features of plastics [2, 11, 13]. We call those non-metallic substances an adhesive, that the firm surfaces with the surface adhesion (adhesion), and their own solidity join (cohesion). The sticking is an operation when a mediatory substance, the mucilage connects the surfaces of the solids with its help, and the peculiarities of the surfaces to be connected do not change. The material to be bonded must fulfil two conditions: - The polymer surface must have adhesion friend

characteristics. This means that a chemical and physical interaction has to come into existence between the mucilage and the surface boundary layer.

- The mucilage has to moisten the polymer. The surfaces energy of plastic has to be higher or equal with the surfaces tension of the mucilage.

In this case, the stock is unsuitable for gluing if these conditions do not come true, or the surfaces demand preparative treatment. 2. EXPERIMENTAL METHODS The Table 1 shows the tested materials and to them owing (the Loctite made a choice based on Technical Data Sheet (TDS) recommendation) adhesive systems [9]. We examined selected materials on the experiment series sticking with themselves and with general construction steel.

Table 1. Gluing experiment plan

Material mates Adhesive Primer Activator PP - PP Superglue: Loctite 406 Primer: Loctite 770

Structural adhesive: Loctite 3035 - PP – S235 steel Superglue: Loctite 406 Loctite 770 just for PP

Structural adhesive: Loctite 3035 - HD1000 – HD 1000 Superglue: Loctite 406 Primer: Loctite 770

Structural adhesive: Loctite 3035 - HD 1000–S235 steel Superglue: Loctite 406 Loctite 770 just for HD 1000

Structural adhesive: Loctite 3035 -


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HD 500-HD500 Superglue: Loctite 406 Primer: Loctite 770 Structural adhesive: Loctite 3035 -

HD 500 - S235 Superglue: Loctite 406 Loctite 770 just for HD 500 Structural adhesive: Loctite 3035 -

PTFE - PTFE Superglue: Loctite 406 Primer: Loctite 770 Structural adhesive: Loctite 3035 -

PTFE – S235 steel Superglue: Loctite 406 Loctite 770 just for PTFE Structural adhesive: Loctite 3035 -

2.1 The strength tests of the bonded connections In this work, the adhesive was prepared as described in the standard specimens. The adhesive strength of the specimens was measured by tensile test. The specimens were made by cutting with length 12,7mm. The bending stress does not interfere with the test samples. Its disadvantage is tensile-tests that not clear shearing stress affects the gluing, identical forming is at disposal of all of the specimens at the same time. The knowledge of the absolute result is not necessary in the interest of the comparison because of this. We executed 5 repetitions in the course of our measurements. The tensile was managed by a Zwick Roell Z100 tensile test machine (Fig. 1.). The maximum tensile load is 100kN of the tensile-test machine. We complied with the requirements of ISO 527 during the measurement.

Fig. 1. Zwick Roell Z100 tension testing machine

2.2 The specimen The specimens used for the gluing were made by sawing from a 2mm thick plate in an identical size. The dimensions of the specimens are shown in figure 2.

Fig. 2. Dimensions of the specimen

We fit the specimens with 12,7mm long overlap to each other, for the forming of the overlap-joint. We chose the lap based on standard DIN EN 1465. The requirements made on the gluing of the specimens: - simultaneously the gluing of 5 specimens, - overlap size are 12,5 +_0,1 mm, - having identical compressive force, - the specimens should not stick to the apparatus.

Fig. 3. The apparatus used for the gluing

We bonded the specimens (what useful for tensile stress test) in the apparatus which can be seen on the figure 3. We bonded two pieces of specimens it can be seen on the figure it together. We degreased the specimens with Loctite 7200 detergents before the bonding. We used Loctite 406 and Loctite 3035 adhesives gluing the specimens. We applied an additional surface primer implement (Loctite 770) activating the surface of the polymer. We treated the plastic surfaces with the primer implement first, and then we placed the necessary adhesive on the specimens and after put again the surfaces on each other. The figure 4. shows the finished specimens.

Fig. 4. Finished PP test bodies (stuck with Loctite 406

adhesives).

We made the bonding according to Loctite Technical Data Sheet (TDS) regulations. The TDS grants the preparation method of gluing surface, the time of adhesive of application and his solidification time.

Ragasztó


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2.3 The tested materials Adhesives The Loctite adhesives what were used are reactionary adhesives. Those wearing up happen in a fluent state, and they are consolidated by a reaction between the surfaces. Loctite gave the adhesives the experiment our series. The table 2. contains he technical data of the selected adhesives. The Loctite 406 is a fast curing, wicking grade viscosity, surface insensitive instant adhesive for post applications. His benefit is that is resists up to 120° temperature and has got low viscosity The Loctite 770 polyolefin primer increases the gluing solidity in case of the polymers which can be stuck difficultly. His fixing time is 2-10mp. It is colourless, transparent material. The Loctite 3035 adhesive is a Polyolefin Bonder, what easy-to-use. 1:1 mix product that store at room temperature and works where traditional low surface energy bonders often fail. Loctite® 3035™ polyolefin bonding adhesive offers the highest in reliability and consistency of performance and has a fast fixture time.

Table 2. Technical data of adhesives Loctite 406 Loctite 3035 Technology Cyanoacrylate Acrylic Chemical Type Ethyl

cyanoacrylate Methacrylate

Components One part without mixing

Two component requires mixing

Cure Humidity Room temp. Working Time, 25 °C, (before assembly):

3min 7 min

Fixture Time 5-10 sec 10 h Full strength 24 h 72 h Shear Strength 8-15 N/mm2 2,5-14 N/mm2

Construction steel (S 235 JR N) Structural steel is a standard construction material, with a low carbon content (max 0.22%) and tensile strength is at Rm= 360-510 N/mm2 disposal generally. The S 235 structural steel plate can be bolted, riveted and welded, glued, in a full range of construction and fabrication including bridges and other general structural projects. It is a well-adhesive materials, adhesives available in the store is well used. The steel can easily be glued, the steels to any developed adhesive structure can be used.

Polypropylene (PP) Polypropylene (PP) is a linear hydrocarbon polymer, expressed as CnH2n. PP, like polyethylene HDPE), is a polyolefin or saturated polymer. Polypropylene is one of those most versatile polymers available with applications, both as a plastic and as a fibre, in virtually all of the plastics end-use markets. The tensile strength at yield of the polypropylene is 30MPa. The lasting one which can be developed difficultly because of the exceptionally small surface energy, strong one is stuck joint. This substance the literature other overlap-joint suggests

forming. In terms of gluing the polypropylene the difficultly can be stuck between substances can be enumerated. UHMW-PE (Ultra High Molecular Weight Polyethylene) Many kinds of polyethylene are known, with most having the chemical formula (C2H4)n. Thus, PE is usually a mixture of similar polymers of ethylene with various values of chemical elements. Two different types are used in the experiment series, the HD500, and HD1000. The tensile strength at yield of the UHMW PE is 20-24 MPa. Polyethylene is of low strength, hardness and rigidity, but has a high ductility and impact strength as well as low friction. It shows strong creep under persistent force, which can be reduced by addition of short fibres. The gluing of the polythene it is important, that without a surface treatment only with special adhesives can be glued together. The adhesives are fit for this purpose if their chemistry and physical construction is consistent with that of the polyethylene well only. Those types are used usually as adhesives witch remain elastic in hardened condition. Polytetrafluorethylene (PTFE) A thermoplastic resin, (C2F4)n, that is resistant to heat and chemicals, has an extremely low coefficient of friction. His tensile strength 16-25 MPa and the elongation is 270-400 %. Because of the construction of the Teflon molecule it cannot be stuck, since the incomparably bigger one fluorine atoms surround totally the coal atoms, a cohesive contact cannot be created with adhesive substance. The chemical stability is good for the Teflon one, and sticking his anti-adhesion surface demands a special procedure. 3 DISCUSSIONS The results of the tensile tests are shown in the next. We glued polymer (PP, HD500, HD1000 and PTFE) and structural steel (S 235 JR N). The tensile test diagram of the examined polymers is visible on the figure 5. We summarized in the table 3. the typical polymer tensile load values.

Fig. 5. The tensile strength diagram of the base polymers


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We made the tensile test according to a standard ISO 527-1. From the diagrams it is verifiable, that PP behaved rigidly, the rest of the plastic behaved toughly. The force marked (with a dot) value exceeded considerable stretching can be experienced on the tensile-test diagram. The specimens do not tear yet due to the metamorphosis, but their shape is lost already, this influences the solidity of the stuck joints significantly.

Table 3. The typical strength of base polymers. Polymer type Force [N]

PP 1723 HD1000 1098 HD500 1269 PTFE 482

In case of polypropylene specimens the gluing can be made difficultly, adhesion overlap-joint does not take shape since the surface energy is small. We treated the surfaces with a primer modifying the surface energy in the course of our gluing experiments. In case of PP specimens the bonding strength made with Loctite 406 glue is only half of the base material strength. It can be seen in figure 6. the “c” diagram shows elastic deformation only. Before the permanent deformation the specimen tears. Higher strength can be reached when PP plastic is glued with steel. It can be seen in “a” diagram that in this case the bonding is stronger, the steel reduces the bonding deformation so it remains longer however the base material elongates already. In case of bonding made with Loctite 3035 adhesive higher strength can be reached due to the elastic adhesive. The PP base material strength can be totally utilized. Sticking together the PP material with steel, higher strength can be reached, then the bonding is stronger than the base material. The polymer elongates according to “b” figure. The glued bonding behaves such as it would be the original material.

Fig. 6. The tensile strength of the PP and S235 JR N mates with different adhesives

It has to be taken into consideration that at gluing the HD100 polypropylene without surface treatment it is difficult the bonding. During our gluing experiment we

treated the surface of specimens with Loctite 770 primer before using the Loctite 406 cement. Figure 7. shows the gluing diagrams of the HD1000 polymer and the steel. Gluing the HD1000 polymer with superglue strong bonding cannot be made. The polyethylene deforms to the effect of tensile loud, so the glue is peeling-off from the surface intermittently. Figure “A” shows a piece-off from the surface so the effect of load, in such a case disruption can be seen in the diagram. High strength can be reached with the Loctite 406 glue at HD1000 and S235JRN materials. The “B” detail of the diagram shows the linear section which means elastic deformation. Then the bonding is stable, the gluing does not breaks. At “C” point the glue is strong then the bonding reaches the strength of the base material. In case of “D” and “E” the gluing lasts for a long time due to the average deformation, it makes possible the polymer elongation.

Fig. 7. The tensile strength of the HD1000 and S235 JR N mates with different adhesives

In case of polyethylene HD500 because of higher strength of the lapped bondage made with Loctite 406 superglue by using suitable primer it can be reached that strength to be equal with the strength of base material. In the case of the HD 500 polymers and steel mates the contact rather from the surface of the steel the adhesive detaches, and this causes the breakdown of the overlap-joint. Figure 8. shows the gluing diagrams of the HD500 polymer and of the steel. Strong bonding can be made when the HD500 polymer is glued with superglue “4”. The polyethylene elongates to the effect of tension load the glued bonding does not get off. The glue peels off from the steel surface so here the glued bonding is weaker, the “3” diagram shows this.

The “1” and “2” diagrams show the tensile-test diagrams of specimens made with Loctite 3035 structural glue. This glue cannot utilize the strength of materials. The glue peels off in the section of the polymer elastic deformation, so the connection between then comes to an end.


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Fig. 8. The tensile strength of the HD500 and S235 JR N mates with different adhesives

Because of the construction of the polytetrafluorethylene molecule it cannot be stuck, namely the greater scale flour atoms encircles the carbon atoms, so they cannot produce cohesion connection with the adhesive. For the Teflon has got good chemical resistance, and anti-adhesion surface. Despite treating the surface with Loctite 770 primer then the strength of the lapped bonding made by Loctite 406 adhesive can reach 75% of the base metal strength. From PTFE surface the adhesive is divorcing partially down in this case, this substantial cross-section decrease can be attributed to this. Figure 9. shows the gluing diagrams of the PTFE polymer and the steel. Strong bonding can be made when the PTFE polymer is glued with Loctite 406 superglue “I”. It can be seen on the diagram that the gluing influences the polymer diagram not at all. However if it is glued, with steel or Loctite 3035 structural glue is used, then weak bonding can be created according to “II”, “III” and “IV” diagrams. The glue inhibits the polymer in the elastic deformation, so it peels off from the surface.

Fig. 9. The tensile strength of the PTFE and S235 JR N

mates with different adhesives

The summarized results of the measuring series carried out by us can be seen in figure 10. It comes so light from our tests gluing the PP, UHMWPE, HD1000, HD500, PTFE plastics with themselves or with a general constructional steel concerning the bonding strength it can reach 50% of the base material strength in the worst case.

In that case if the polymer has to be glued with steel, then it is suitable choosing such glue which utilizes the steel higher strength, and connects whit the polymer surface stronger hereby higher bonding strength can be reached. In that case when polymer with polymer has to be glued then it is suitable choosing optimal glue concerning the given material.

Fig. 10. The strength of the stuck overlap-joints of the examined polymers due to the base polymers

It can be established based on our measurements that with Loctite 406 superglue results good bonding strength in case of polymer and steel connection, however the bonding strength of glues of the PP and HD1000 materials is 50% altogether of the base material strength. In case of (being difficultly glue able) if it is inhibited the cross-section decrease due to the effect of elongation, for example with steel gluing, it’s bonding strength approaches the base material strength.

4 CONCLUSION Based on the measurements done by us it can be established that in the case of polymers rated glue able hardly or not at all could produce simple lapped bonding having strength nearly equal with the strength of base material. The experimental data suggest the following conclusions:

• There is a general rule that it must take into account beyond the properly prepared, cleaned surface, activated with primer the strength properties of glued materials or material pairs.

• The rigid glues have a good effect on the brittle polymers. There is very important to mention that rigid adhesives detach from the surface (because of the deformation). In the former case the soft elastic structural adhesives are the more beneficial ones.

• The adhesive should be preferred which is more optimal for the steel to reach the optimal connection between polymer and steel.

• We can implant a metal plate between glued bonding of polymer-polymer, so we can produce a more rigid bond. This little modification can


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results smaller deformation and lower load on the glued bonding, other case the built in rigid part will be to the whole structure.

Aknowledgement This research work is supported by OTKA K 113039. REFERNCES

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Authors addresses 1Róbert Keresztes, PhD, associate professor, Institute for Mechanical Engineering Technology, Szent István University, Páter Károly u.1, Gödöllő, Hungary 2 Zoltán Szakál PhD, Attila, Kári-Horváth, Tamás Pataki, lecturer, Institute for Mechanical Engineering Technology, Szent István University, Páter Károly u.1, Gödöllő, Hungary

3Ádám, Sarankó, PhD student, Institute for Mechanical Engineering Technology, Szent István University, Páter Károly u.1, Gödöllő, Hungary 1Attila, Kári-Horváth, Tamás Pataki, PhD, lecturer, Institute for Mechanical Engineering Technology, Szent István University, Páter Károly u.1, Gödöllő, Hungary

Contact person 1Róbert Keresztes, [email protected]

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