What Us The Best Strongest Bonding Repair Material For.plastic Ial

Introduction

Plastic objects and materials accept become a big part of our cultural heritage in the last hundred years. Objects of plastic, or containing parts of plastic material, are nowadays in collections of art, cultural history, and pattern. Research about the preservation of plastics has, to a great extent, focused on preventive measures and at present the need for an investigation into more agile preservation methods is evident.

Damage such as cracks and breakage will occur with handling and the process of fourth dimension, and there are occasions when an adhesive bonding is necessary. For preservation purposes, it is of import to cull an adhesive that volition exist stable over time and have as little touch as possible on the object. This article will outline the electric current study into the long-term furnishings of agglutinative joining of polystyrene, one of the most mutual plastics in collections today.

Mainly, this project has investigated the behaviour of the substrate and adhesive through a comparing of before and later accelerated ageing and before and afterwards joining of the plastic and adhesive. Aspects of the written report were deterioration of plastic and adhesive join, working properties, and visual alter through assessment of working properties, appearance, color measurement, tensile testing, hardness measurement, cess of break type, and scanning electron microscope (SEM) imaging. In addition, an assessment of reversibility was included.

Background

The starting signal for this investigation was a prior projection at The Swedish National Heritage Lath 2005–2008 concerning harm, degradation, and analysis of plastic materials in Swedish museum collections (Nord et al., 2008). A survey including 51 Swedish museums and a more extensive damage assessment of plastic objects at 9 museums were performed. The museums mainly consisted of collections of cultural history, but also art and design museums were included. The project ended that there was a need for farther research into active conservation methods for the preservation of plastic materials. The area of adhesive joining was called and a enquiry project at the Swedish National Heritage Board together with KTH Imperial Institute of Engineering science and the inquiry institute Swerea KIMAB was undertaken in collaboration with a peer review panel of conservators.

The repair and reattachment of broken or damaged objects tin can be considered necessary for several reasons, such as increasing the understanding and estimation of the object or as a mensurate to prevent further degradation. The conservator will need to know which agglutinative can exist used for which kind of plastic, how it can affect the object, and how information technology will age. The damage survey of Swedish collections showed that polystyrene is one of the most frequent plastics displaying breaks and cracks (Nord et al., 2008). This report contributes to the knowledge of the long-term effects of adhesives on polystyrene objects.

The need for finding an appropriate adhesive for the repair of polystyrene has been pointed out by conservators (Moomaw et al., 2009). Inquiry into adhesives for plastic materials in conservation has been performed for poly (methyl methacrylate) and unsaturated polyester but not systematically for polystyrene (Sale, 1995; Comiotto & Egger, 2009; Laganá & van Oosten, 2011; Roche, 2011; Sale, 2011). This written report is designed to expect at the interaction between substrate and adhesive, not merely at the functioning of the agglutinative itself. The results volition give conservators guidance in choosing adhesives in their work to preserve our cultural heritage.

Polystyrene has been in product since the 1930s, the primeval recorded product is from 1931 by BASF in Europe and from 1938 by Dow chemicals in the US (Sheirs & Priddy, 2003). General purpose polystyrene (GPPS) has been used as testing material in the current project, a plastic consisting of polymer chains of the styrene monomer and additives. Polystyrene is an amorphous thermoplastic with a glass transition temperature (T _yard) of around 100°C and tin be both transparent and opaque (Sheirs & Priddy, 2003).

Materials and methods

Plastic and adhesives

Rigid polystyrene (GPPS) was the plastic for this report. Extruded transparent plastic sheets of 1-mm thickness manufactured past Nudec were used as test material. The principal impetus for the choice of adhesives was what adhesive would conservators use, or think of using, for polystyrene. A questionnaire was therefore sent to Swedish conservators likely to come up across polystyrene in their work. Replies from approximately 20 conservators formed the basis for a screening exam trial of 20 adhesives (Appendix I for adhesives in the initial screening). After initial testing which included because working properties, aesthetics, and damaging effects seen on visual inspection, and through discussions with the peer review panel, information technology was narrowed down to vii adhesives for further investigation. The adhesives chosen stand for both conservation grade variants commonly used by conservators and some more industrial products. They fall mainly into three categories: acrylates (solvent based or dispersion), epoxies, and one cyanoacrylate (see Table 1 for a list of the called adhesives and data). The solvent-based acrylates were Paraloid^® B-72 in acetone: ethanol, Paraloid^® B-72 in merely ethanol, Paraloid^® B-67 in isopropanol, and Acrifix^® 116. The epoxies were HXTAL^®-NYL-1 and Araldite^® 2022. The acrylate in dispersion was Primal^® AC 35 and the cyanoacrylate was Loctite^® Super Attack Precision (Table i). The projects' emphasis on usage or potential usage of adhesives on polystyrene might have led the study to include adhesives that theoretically did not run into all requirements from a heritage perspective, e.thousand. adhesives with solvents dissolving polystyrene or adhesives with a different refractive index than polystyrene. The idea was to investigate empirically how those adhesives which were selected equally potential candidates for polymer adhesion would conduct over time and if or to what extent damage would occur. If there was a choice betwixt adhesives that behaved similarly in the screening exam then data from the industry and in the literature (Shashoua 2008; Horie 2010) was used for guidance. Those with more than compatible qualities with polystyrene in terms of such aspects as glass transition temperature, ageing qualities, or reversibility were so chosen.

Table 1. Listing of chosen adhesives and basic information*

Experimental

Accelerated ageing was performed past light ageing using a 430-watt Sol 500 lamp with a metal halide calorie-free bulb in the ultraviolet and visible range (295–780 nm) from Hönle UV technology. The samples were placed flat at a altitude of 70 cm from the light source and rotated once a week. Lux levels, ultraviolet-A (UVA) levels, relative humidity (RH), and temperature were recorded at 22 measuring points once a week. The samples were exposed to an average of 30 600 ± 3300 lux and a UVA component of 13 ± 1.7 W/one thousand² at 26–28°C and 44% ± 1% RH. Based on average lux levels, the ageing menstruum was fix to 24 days in order to simulate 60 museum years.

The experiments were conducted in two series (see menstruum charts in Figs. 1 and two). In series 1 (S1), fourscore samples, 50 mm × 100 mm × i mm in size, were initially subjected to pull-to-interruption in the tensile tester to simulate a break edge. During the initial pull-to-break of the polymer samples, the samples slipped out of the clamps or shattered into several pieces. A shattered surface was impractical as a pause face, and therefore a 0.3–0.2-mm notch was made with a scalpel across the face of the sample in order to help breaking of the samples. The samples then bankrupt along the notch face and created a continuous, direct break during the pull-to-break.

Figure 1. Flow chart of sample testing of adhered edges, series 1 (S1).

Effigy 2. Flow chart of testing of samples with an open layer of adhesive, series 2 (S2).

The straight, continuous broken edges of the plastic were then abutted and joined using the unlike adhesives mentioned in a higher place. Working backdrop and visual appearance were assessed prior to 40 of the unaged samples existence subjected to pull-to-intermission in the tensile tester (five for each adhesive). The remaining xl samples were subjected to low-cal ageing (5 for each adhesive) before a new visual assessment followed by tensile testing. Break force values were compared and the type of break assessed. In S1 all adhesives were applied on break edges with a brush except for Loctite^® Super Assail Precision (Loctite^® SAP) which was practical directly from the nozzle of the tube. After application of the adhesive, the adhered pieces were pressed together and laid flat to cure. Tensile testing of unaged samples was conducted after v days of curing. In addition, polystyrene without agglutinative was included in the tensile testing before and after ageing as reference samples.

In series 2 (S2, Fig. 2), 1-mm-thick adhesive layers were practical with a draw-down technique to cover the centre of viii polystyrene samples (Fig. 3), 108 mm × 215 mm × 1 mm. Due to a dissimilar charge per unit of shrinkage during curing, the adhesive layers differed in thickness. The epoxies had a thickness of i mm after curing, Paraloid^® B-72 in acetone: ethanol 0.30 mm, Paraloid^® B-72 in ethanol 0.50 mm, Paraloid^® B-67 0.xxx mm, Central^® Air-conditioning 35 0.60 mm, Loctite^® SAP 0.50 mm, and Acrifix^® 116 0.25 mm. All samples were cut in half, and one half was subjected to lite ageing for 24 days. Visual assessment, hardness testing, colour measurement, and SEM imaging of the border area of agglutinative and plastic were conducted and compared on both unaged and aged samples. For colour measuring, a set of the adhesives with glass equally a substrate was included. Colour measurements were taken after eight days of curing for unaged samples. Hardness testing was performed later nine days of curing for the unaged samples.

Figure three. Instance of HXTAL^®-NYL-one on transparent polystyrene of test serial 2 (S2) before ageing and before cutting. The adhesive covers the centre department.

Instrumental

Colour measurement values were taken with a Spectrophotometer CM-2600/2500d (Konica Minolta, Langenhagen, Germany) to measure the adhesives on the plastic, the adhesives on a glass substrate, and on the plastic without adhesive. Measurements were taken with a white A4 paper under the substrates, and three measurement points were taken for each agglutinative. The ΔE* value is a single value based on calculations of the difference between the L*, a*, and b* value of a measured sample and a called standard or target to illustrate color alter or colour shift. The ΔE* calculations are based on the ΔE* CIE1976 standard. For the adhesive measurements, the standard or target used was unaged polystyrene as a base line color reference for modify over time.

Hardness testing was done with a Male monarch Durometer (Rex Gauge Company, Inc, Buffalo Grove, Illinois, USA), Model MSDD-three-A, B, O in accordance with ASTM D-2240. The hardness testing was done with the MS-O 0209 pencil head designed for soft materials like textiles, condom, and gums. In this example, it is believed that the MS-O type will give the virtually accurate readings since the thinness of the adhesive layers requires a very sensitive measuring head. Iii measurement points were taken for each sample and the average calculated.

Tensile testing was conducted with a Shimadzu AGS-x 10N-10kN tensile tester, gauge length sixty mm, load cell 1000 North, 100 mm/min, and the information were processed using Trapezium Lite X software.

SEM analysis was performed using a LEO 1455VP (Oxford Instruments) with Inca 400 software. Conditions used during testing were an EHT (electron loftier tension) ranging from 20 kV, iprobe ane.0 nA, backscattering, with variable pressure. Magnifications used were ×xviii, ×100, ×250, and ×1000. Samples were sputter coated with gilt for 60 seconds at xviii mA to increment conductivity and therefore visibility of fractures in the plastic fabric. SEM imaging was also done on unsputtered samples. Free energy-dispersive Ten-ray spectroscopy (EDX) mapping fourth dimension was 820 seconds.

Results and give-and-take

Cess of working properties, advent, and colour measurement

The viscosity and the work time of the adhesive were the 2 well-nigh important factors in assessing working properties. The epoxies and the Loctite^® SAP had very low viscosities which fabricated them hard to apply in a controlled style. Paraloid^® B-72 was easier to employ dissolved in ethanol only rather than in acetone: ethanol, since ethanol increased the working time and kept information technology from thickening too fast during awarding (Table half dozen). This gave more control and led to a visually cleaner result. Among the seven adhesives Acrifix^® 116 was the easiest to use and about controllable during awarding, mainly because information technology has a relatively high viscosity and long working time. Primal^® AC 35 was as well relatively easy to utilise. With both of the epoxies, delamination from the plastic surface occurred when subjected to stress while cutting of S2. The epoxies did not adhere well to the smooth polystyrene surface compared to the other investigated adhesives. This could also exist seen in the results during assessment of the type of pause of the joins in the tensile testing for S1, where the epoxies were the only adhesives resulting in a break betwixt the plastic and the agglutinative.

All adhesives except for the epoxies experienced shrinkage subsequently curing. Acrifix^® 116 and the Paraloids shrank the most due to the evaporation of solvents and in the case of Acrifix^® 116, it acquired the most harm through the plastic visibly bending into a concave shape upon curing (Fig. 4).The bending is caused by a combination of factors. The solvent mixture in the agglutinative dissolves the polystyrene and increases the ability for the polymer chains to move (Fried, 2003). When the adhesive contracts during evaporation of the solvent with subsequent shrinkage, a tension is created giving ascent to the deformation. Loctite^® SAP caused some slight bending of the plastic but less than Acrifix^® 116. None of the other adhesives caused any deformation or impairment observed during visual inspection. Looking at Hildebrand solubility parameters the xviii.6 MPa^1/2 of the ethyl acetate in Acrifix^® 116 is very close to that of polystyrene; 18.7 MPa^1/2. Besides that of acetone of 20.four MPa^1/ii is within the 2 MPa^1/ii difference range of dissolution. No deformation could exist seen for the samples with acetone containing adhesive though, nor was at that place any visible effect on the plastic from the solvents in the joins of S1. Ethanol and water on the other have Hildebrand solubility parameters of 26.6 MPa^1/ii and 47.vii MPa^ane/two, respectively (Shashoua, 2008). Information technology has to exist remembered that the solubility of the plastic tin change with ageing.

Figure 4. Bending of a polystyrene sample with Acrifix^® 116 in a band in the center of the sample.

All adhesive bonds were visible after curing. The visibility of the bonds shows that none of the adhesives have the same refractive index as the polystyrene, i.59 (Kasarova et al., 2007). A microscopy study of the different agglutinative bonds in S1 showed that Acrifix^® 116 gives the thinnest bond. Stress not bad on the border of the plastic joins was non visible during inspection or in the stereomicroscope before or afterwards ageing for any of the adhesives. Information technology should exist remembered that stress cracking tin develop over fourth dimension with natural ageing every bit other environmental factors tin can play a part, non simply calorie-free ageing. Also, the degree of deposition in aged materials prior to adhesion may increase the hazard of stress cracking.

The 2 Paraloids were the only adhesives that formed a substantial amount of bubbles in the joins of S1. Paraloid^® B-67 formed more bubbles than Paraloid^® B-72 and had, in full general, a very uneven surface after curing in the layers of S2. Paraloid^® B-72 in acetone: ethanol and Paraloid^® B-72 in only ethanol formed approximately the same amount and size of bubbling. The epoxies and Primal^® AC 35 show basically no bubbles while Acrifix^® 116 had some and Loctite^® SAP only had a few. After ageing, the polystyrene showed an increased tendency to fissure for the samples with Loctite^® SAP, Acrifix^® 116, and Paraloid^® B-67 when being cut in preparation for SEM imaging. The extent to which the epoxies delaminated from the plastic increased after ageing.

All adhesives were transparent in color before ageing except for Primal^® Air conditioning 35, which was slightly pale yellowish and Loctite^® SAP which was pale white. Loctite^® SAP also had an uneven, grainy texture. The most apparent visible change in S2 after ageing was color change. Too the control sample of plastic without adhesive yellowed visibly. Among the adhesives the Loctite^® SAP and Araldite^® 2022 showed the most astringent yellowing in the visual inspection after ageing for both S2 and S1. HXTAL^®-NYL-ane and Acrifix^® 116 showed no visible colour change.

Upon visual inspection, most yellowing was seen in the open layer samples (S2) and not in the adhesive joins of the adhered edges (S1). This is non surprising every bit in S2 at that place is a larger surface area exposed to calorie-free than in the much smaller adhesive bring together. Past visual inspection yellowing was credible for the joins of Araldite^® 2022 and Loctite^® SAP in S1. The Araldite^® 2022 has been shown to xanthous in earlier investigations (Down, 1986). The ii epoxies showed a difference in colour change where the HXTAL^®-NYL-i did non visibly yellowish while Araldite^® 2022 did. The DGEBA (butanedioldiglyciyl ether) component of the Araldite^® 2022 has been noted to yellow in light ageing (Horie, 2010). Severe yellowing for epoxies could exist attributed to the amine-structure nowadays as a catalyst (Down, 2001). The non-yellowing quality of HXTAL^®-NYL-1 has been shown in earlier studies (Down, 2001; Coutinho et al., 2009; Sale, 2011). The 2 Paraloids experienced the same amount of visible yellowing. In before ageing studies, B-72 yellowed more than B-67 during light ageing (Down, 2009).

The spectrophotometry measurements on S2 mirrored the visible color changes before and after ageing (Table ii). The curves showing reflectance in the visible wavelength spectrum and the b* values before and subsequently ageing differ the least for Acrifix^® 116 and the almost for Loctite^® SAP (Fig. 5) (b* scale measures yellowness [positive b] to blueness [negative b]). The a* values (a* measures redness [positive a] – to greenness [negative a]) showed the same tendencies every bit the b* values in terms of greatest alter before/after ageing. Loctite^® SAP and Araldite^® 2022 inverse the most, towards greenness, after ageing. L* value describes black/white on the colour scale, 0 yields black and L* = 100 indicates diffuse white.

Figure 5. Curves showing % reflectance in the visible spectrum before and after ageing. The greatest color change could be seen for Loctite^® SAP and the least for Acrifix^® 116.

Table 2. The spectrophotometer 50, a, b* and ΔE* values for adhesives on open up layer samples (S2), and on reference samples of plastic^†

The b* values for the plastics without agglutinative showed an increase by 3 reflecting the yellowing of the plastic itself (Tabular array 2). When the adhesive is close to transparent and very thin, the spectrophotometer about likely also measures the color of the substrate underneath. To measure colour change of the adhesive only, the adhesives were subjected to ageing with drinking glass every bit a substrate (Table 3). The Acrifix^® 116 showed the least change with a difference of i while Loctite^® SAP showed the largest change in the b* value with a divergence of 10.2. The HXTAL^®-NYL-ane did not show as great a difference in ΔE* on glass as it did on the plastic which indicates that the plastics yellowing during ageing may be reflected in the ΔE* values. It is worth noting that Loctite^® SAP is the just adhesive which has gone from negative values (blue) to positive (yellow) in b* value later on ageing when measured with glass as a substrate.

Tabular array 3. The spectrophotometer L, a, b* and ΔE* values for adhesives on glass^†

Tensile testing, type of break, and hardness measurement

All samples bankrupt in the adhered expanse with no visible harm to the plastic such as shattering, stress cracks, or loss of material. See Fig. 6 for boilerplate intermission force sensitivity and Appendix II for numerical values. There is a spread to the values probably introduced as the awarding of adhesive was performed manually. Tensile forcefulness measurements are too normally associated to a significant data handful due to occurrence of small defects present in the test specimens. Still, taking this uncertainty into business relationship the results are interpreted as applicable in an overall assessment of the general trends.

Figure 6. Tensile testing of agglutinative joins. UA, unaged; A, aged; GPPS, plastic without adhesive.

The adhesives showed approximately the aforementioned break forcefulness sensitivity level in relation to each other before and after ageing ranging highest to lowest in break force sensitivity; Loctite^® SAP was the strongest adhesive and Paraloid^® B-67 and Primal^® AC 35 were the weakest, while Acrifix^® 116, Araldite^® 2022, HXTAL^®-NYL-1, and Paraloid^® B-72, both in ethanol and acetone: ethanol, are relatively close together in the mid range. The plastic without adhesives have higher values for suspension forcefulness sensitivity than for any of the adhered joins.

The average break force sensitivity values indicate that Loctite^® SAP has weakened afterwards ageing while Acrifix^® 116 and Key^® Air conditioning 35 showed increased break force sensitivity after ageing on both plastics. Information technology has been reported that cyanoacrylate adhesives are prone to photo-induced ageing with possible chain scissioning which could be in process here equally the transparency enables the radiation to attain the adhesive (Horie, 2010). The tendency for Acrifix^® 116 (acrylate in solvent mix) and Key^® AC 35 (acrylate dispersion) to increase in strength by calorie-free ageing could exist due to a prolonged curing procedure.

The epoxies accept a medium break strength sensitivity amongst the tested adhesives, fifty-fifty though epoxies in general are considered to be very strong adhesives. This points to a failure of adhesive character in this case. The epoxies' relatively weak adherence on polystyrene is too seen in a delamination from the plastic observed in the open layer samples when cutting. This could be attributed to their lack of affinity with non-polar surfaces. The non-polar surface of polystyrene repels the adhesive upon awarding which results in low wetting and a weakened bond in comparison to behaviour on more polar substrates. This is reflected in the fact that the surface tension value of polystyrene is lower than that of epoxy, 33 mN/m compared to 47 mN/m at 20°C for epoxy (Shashoua, 2008). Acrylics have 32 mN/m at 20°C and cyanoacrylates 37 mN/m and should hence moisture the substrate more effectively (Shashoua, 2008). Information technology is important to consider that for objects in heritage collections the surface tension value may be increased compared to the value of unaged polystyrene. This could lead to better wetting and stronger bonding than for joins of unaged polystyrene. It has been reported that the forcefulness of Araldite^® 2022 increases during low-cal ageing which is idea to be a effect of cross-linking (Coutinho et al., 2009); however, this is not reflected in the average value of pause force sensitivity for the samples of Araldite^® 2022. On the other hand, the values for hardness measured on open layer samples of Araldite^® 2022 increased with exposure to light (Fig. 7). This could indicate cross-linking in the open layer with a greater surface area exposed to the calorie-free compared to the adhesive of the joins.

Figure 7. Hardness earlier and later on ageing. UA, unaged; A, aged; GPPS, plastic without adhesive. The values for Acrifix^® 116 were not valid due to the deformation of the sample.

There is a departure in suspension force sensitivity betwixt the 2 Paraloids; with Paraloid^® B-72 being clearly stronger than B-67. The brittleness of the B-67 observed during hardness testing could be a factor in breakage. Both Paraloids have bubbling in the agglutinative bond, merely Paraloid^® B-67 specimens have a larger number than Paraloid^® B-72. This could too business relationship for the weak bail as there is less joined surface between the adhesive and the plastic. The brittleness of B-67 has been shown in earlier studies (Down et al., 1996, 2009).

The type of suspension was studied by SEM and by stereomicroscopy. SEM images were made normal to the break edges, viewing the break edges from above. None of the samples experienced a break in the plastic (Table 4). This can be seen in relation to the fact that the polystyrene is stronger than the adhesives, which results in a break either in the agglutinative (cohesive interruption in the adhesive) or between the agglutinative and plastic (adhesive break). All acrylates in solvent; the Paraloids, and Acrifix^® 116, experienced a break in the adhesive. Both epoxies experienced breaks betwixt the adhesive and plastic. It is interesting to annotation that the trend to delaminate from the plastic every bit seen in the sample preparation of the open-layer samples in S2, also occurs on a rough polystyrene break border surface and not only on a smooth surface. Primal^® AC 35 and Loctite^® SAP experienced a combination of interruption in the agglutinative and between adhesive and plastic.

Tabular array 4. Assessment of type of interruption on samples from tensile testing (S1) based on viewing in stereomicroscope and past SEM-imaging.

The adhesives and the plastic were tested for hardness earlier and afterward ageing on open layer samples of S2 (Fig. seven). The plastic was harder than about of the adhesives, except for the epoxies. The epoxies were as difficult every bit the plastic with the exception of unaged Araldite^® 2022. The softest adhesives were Central^® AC 35 and Paraloid^® B-67. The values for Acrifix^® 116 were non valid due to the deformation of the sample. For Paraloid^® B-67 miniature fractures acquired past the durometer pencil during hardness testing was visible. The durometer did non crusade fractures in whatever of the other adhesives.

Based on the measurements, a general tendency is that both plastics and all adhesives harden with ageing. Paraloid^® B-72 and HXTAL^®-NYL-i changed the least later on ageing while Paraloid^® B-67 and Cardinal^® AC 35 changed the most. This can exist a result of cross-linking in the adhesives caused by low-cal ageing or a standing procedure of curing. It has been pointed out by Wolbers (2008), in relation to long-term ageing of acrylics, that there is a procedure of loss of retained solvent which volition affect their brittleness and drinking glass transition temperatures. The acrylics have too been shown to become less flexible during dark ageing (Downward et al., 1996). From a conservator's point of view, hardness measurement is of interest as a means of understanding how the agglutinative and substrate age and part together. The property preferred is that the adhesive should not be harder than the plastic, and this is the case for most of the investigated adhesives apart from the epoxies which are on a similar level.

Effect and harm on plastic from agglutinative seen in SEM

The S2 samples were observed at the edge area where the adhesive covers the plastic, viewed normal to the plastic surface (Figs. 8 and nine). The view shows the edge area from above with one part where the adhesive covers the plastic (to the correct) and one part showing merely the plastic surface (to the left in the images). The focus was to make up one's mind whether the adhesives caused whatever damage to the plastic on a micro level, and images of before and later ageing were assessed. Studying the samples using SEM showed damage to the plastic for ii adhesives: Loctite^® SAP and Acrifix^® 116 (Fig. 8).

Figure 8. SEM image of sample with Acrifix^® 116. Adhesive to the right covering the plastic of S2 sample. Viewed normal to the surface of the plastic. Gilded sputtered. Cracks are visible in the plastic along the border of the adhesive.

Figure 9. SEM image of sample with Loctite^® Super Attack Precision. Adhesive to the right roofing the plastic of S2 sample. Possible impairment to the plastic seen as a surface blueprint of darker and lighter areas to the left. Viewed normal to the surface of the plastic. Gold sputtered.

For the samples with Acrifix^® 116 both unaged and aged showed cracks in the plastic at the edge area forth the edge of the adhesive (Fig. 8). The cracks became slightly worse after ageing, which could be related to the prolonged drying of the adhesive. The stresses increment as a shrinkage of the adhesive occurs. It is interesting to note that the samples with dissolving solvent acetone for polystyrene did not show any visible damages on a micro-level for either aged or unaged.

In the instance of Loctite^® SAP some irregular surface features in the plastic forth the edge of the adhesive could be seen. This tin can be interpreted every bit damage to the polystyrene caused by the adhesive (Fig. 9). The phenomenon was likewise visible in the low-cal microscope. At that place were also some cracks in the plastic along the edge of the adhesive.

1 sample of Loctite^® SAP was subjected to elemental assay by EDX to determine whether the irregularities observed on the plastic surface in the SEM images could be adhesive spill rather than damage to the plastic. It was expected that more than nitrogen would be observed in the adhesive than in the plastic. The nitrogen-mapping, however, gave inconclusive results. The carbon-mapping on the other mitt, gave indications that the irregularities observed are in the plastic itself and not agglutinative spill. The expanse of the adhesive showed much less intensity for carbon. The pattern in the plastic area was not seen in the EDX-mapping every bit less carbon. Had the pattern of darker and lighter areas of the SEM image been a spill of cyanoacrylate, the same pattern would take been visible as less carbon in the mapping, and possibly as more than oxygen.

Information technology has been shown that cyanoacrylates can mix with polycarbonate while curing (Bleed et al., 1985) and a like process might be indicated hither. Internal shrinkage of cyanoacrylates upon curing and possible diffusion into the plastic has also been shown to occur by Vestergaard and Horie (1996).

Assessment of reversibility

The possibility to remove the agglutinative was assessed by attempting to remove or dissolve the adhesive left on the break edges of S1 samples with a scalpel, wooden toothpick, water, ethanol, acetone, and isopropanol. The choice of solvents was based on what would be commonly used by conservators. Results were observed under the microscope. Whatsoever possible damage or dissolving of the plastics was also assessed (Table 5).

Table 5. Results for trials of removing on S1*

The unlike adhesives demonstrated the aforementioned reversibility results after ageing as before ageing, apart from the fact that a larger corporeality of solvent was needed and it took a longer time for the adhesives to dissolve later ageing. Reversibility was possible for the Paraloids and the dispersion Key^® Air-conditioning 35. It was possible to remove the epoxies and Acrifix^® 116 manually with a wooden toothpick with some difficulty. The other adhesives were not possible to remove without the gamble of damaging the plastic. The cyanoacrylate was the nigh difficult to remove.

Overall cess

Based on all of the experiments carried out in series 1 and 2, no single agglutinative appears as clearly superior to the others or to be recommended in full general for use on all polystyrene plastics (Table vi). This is not only because all of the adhesives had some areas where they demonstrated a clear weakness, only too considering the option of adhesive must be seen in relation to the object in question, and depending on what qualities are sought. All the same, some conclusions can be drawn based on the testing, at to the lowest degree in relation to which adhesives that should not be recommended from a heritage perspective.

Tabular array 6. Overall cess of adhesives

Fifty-fifty though Acrifix^® 116 showed some very good qualities both in relation to ageing, full general aesthetics, and working properties, it damaged the plastic through astringent bending in S2 and micro-cracking seen in the SEM. The increased break force sensitivity after ageing might likewise betoken some unwanted strengthening of the bail.

If choosing an epoxy ane should not expect it to be as strongly adhered on polystyrenes equally information technology is generally known to be on other materials. This was observed during testing as delamination from S1 and S2. Among the epoxies, HXTAL^®-NYL-1 yellows far less than Araldite^® 2022 when anile.

If a very strong bond is needed, a cyanoacrylate might be an alternative among the tested adhesives, but the take chances of a break in the plastic rather than in the adhesive bond must exist considered. Moreover, the damaging affect seen in SEM imaging and a deformation of S2 samples enhance questions on its suitability. In addition, the yellowing and non-reversibility need to be taken into account.

Both Paraloids showed proficient ageing qualities, but Paraloid^® B-72 appeared superior to B-67. Paraloid^® B-67 showed a very weak bond and great brittleness both before and after ageing. Paraloid^® B-72 should preferably exist mixed in ethanol rather than in acetone: ethanol due to the risk of acetone damaging the plastic though no damage was observed during testing. It has to exist remembered that for already aged objects there is a greater risk of impairment by solvents due to material deposition. Testing also demonstrated enhanced working properties of Paraloid^® B-72 when mixed only in ethanol. If choosing a Paraloid^®, one should be aware of the difficulty in achieving a very clean, thin bond due to the risk of bubbles in the adhesives. If a relatively weak bond and a white or stake xanthous colour is wanted or accepted, Primal^® Ac 35 can be an alternative based on its good working properties, easy reversibility, and no detected damaging effects.

Information technology should be noted that none of the tested adhesives match the refractive index of polystyrene (i.59) and therefore all joins are visible on transparent plastic. The difference for a friction match should exist less than 0.02 and such adhesives should exist included in hereafter studies. Health aspects in handling these adhesives need to be considered especially for the hardeners of the epoxies (corrosive) (Tabular array six).

Summary and conclusions

In order to contribute with further cognition to guide conservators in their decisions in active conservation of polystyrene, seven adhesives were tested for their effect on the plastic material before and later light ageing. The master aim of this investigation was to observe the stability of the adhesives that are used by conservators and how the join will historic period past studying the consequence of the adhesives on the original fabric. Furthermore, the question of reversibility has been considered.

Methods applied were cess of working properties, advent, colour measurement, tensile testing, hardness measurement, assessment of break type, SEM imaging, and assessment of reversibility. Ageing has been performed by light ageing with a UVA component.

The master accent for the choice of adhesives was what agglutinative would conservators use, or remember of using, for polystyrene. Replies from a questionnaire to conservators formed the footing for a screening test trial of 20 adhesives. Subsequently initial testing which included considering working properties, aesthetics, and damaging effects seen on visual inspection, and through discussions with a peer review panel, it was narrowed downwardly to seven. The called adhesives were acrylates in solvent (Paraloid^® B-72 in acetone: ethanol 1:1, or in only ethanol, Paraloid^® B-67 in isopropanol and Acrifix^® 116), one acrylate dispersion (Cardinal^® AC 35), two epoxies (HXTAL^®-NYL-one, Araldite^® 2022) and one cyanoacrylate (Loctite^® Super Assault Precision (SAP)). They were tested on extruded sail material of transparent full general purpose polystyrene applied on border joins (of butt join type) and as an open layer.

A damaging effect to the plastic could exist seen for Acrifix^® 116 and Loctite^® SAP by visual inspection and on a micro-level past SEM imaging for the open layer samples. Stress great of the plastic on the plastic edge joins was non visible by human eye or in the stereomicroscope for any of the investigated adhesives. For the cyanoacrylate, a surface issue on the plastic was visible in the SEM. The tensile strength of the adhesive for the open layer sample joins was not severely affected during ageing for well-nigh of the tested adhesives. A decrease in average intermission force sensitivity showed a weakening of the cyanoacrylate and for Acrifix^® 116 there was an increase in average interruption force sensitivity after ageing. In full general, the cyanoacrylate was the strongest and Paraloid^® B-67 and Primal^® AC 35 the weakest. None of the adhesives resulted in a cohesive break in the plastic when the joins were subjected to pull-to-break in the tensile tester. Adhesive breaks could exist seen for the epoxies.

Almost adhesives showed yellowing, autonomously from Acrifix^® 116 and only to a minor extent HXTAL^®-NYL-1 on the open layer samples, seen through both visual inspection and in the spectrophotometer measurements. None of the tested adhesives matched the refractive index of the polystyrene and this resulted in the bonds beingness visible. The bonds of the border joins for the cyanoacrylate and Araldite^® 2022 showed visible yellowing. Deformation of the samples with an open layer of agglutinative could be seen for Acrifix^® 116 and to a lesser extant for Loctite^® SAP. Reversibility was possible for the Paraloids and the dispersion Cardinal^® Air-conditioning 35. The epoxies and Acrifix^® 116 was possible to remove manually. The cyanoacrylate was not possible to remove.

During this investigation none of the tested adhesives proved to be ideal for polystyrene. If a weak bail is acceptable, the acrylate dispersion could exist chosen equally information technology was observed to accept no damaging consequence on the plastic and was reversible. HXTAL^®-NYL-i could too be an acceptable alternative as information technology showed no damage to the plastic during testing and had a not-yellowing quality. Possible disadvantages for these adhesives could exist the difficulty in application for the epoxy and a slightly yellow colour for the dispersion. The greatest potential for damage was indicated past Acrifix^® 116 and the cyanoacrylate equally cracking of the plastic could exist seen in the SEM imaging.

Ideally an agglutinative should be able to concur pieces together for the intended usage, and within conservation it should be able to be separated without damage. When choosing an agglutinative for an object in a heritage collection one needs to consider aesthetic aspects, the history of the object, its status, every bit well as future use with expected stresses. Knowing the behaviour of the investigated adhesives and how they age together with polystyrene will guide conservators in making informed choices for polystyrene materials.

Time to come aims

This investigation merely focused on light ageing as this is a factor most likely to affect the object in a museum environment. On the other hand, it is necessary to study physical ageing with other methods of accelerated deterioration to fully apprehend the ageing processes. Information technology would besides be of interest to age plastics and adhesives naturally, i.east. to monitor them in a museum environs over a longer period of time.

Here only a limited number of many possible adhesives were studied and more adhesives demand to exist tested. The possibility to first historic period, or use real objects, so adhere would contribute with knowledge on how aged materials function together with the adhesives. Finally, a further study of the phenomenon initiated by the cyanoacrylate adhesive on the plastic where a surface design could be seen would exist of interest.