Synthesis and properties of solid structural adhesives

© 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

https://doi.org/10.1016/j.ijadhadh.2011.10.006

Synthesis and properties of solid structural adhesives modified in-situ using 1D and 2Dtype microfillers

Agnieszka Kowalczyka*, Krzysztof Kowalczykb, Zbigniew Czecha a. West Pomeranian University of Technology in Szczecin, Institute of Chemical Organic Technology, ul. Pulaskiego 10, 70-322 Szczecin, Poland b. West Pomeranian University of Technology in Szczecin, Polymer Institute, ul. Pulaskiego 10, 70-322 Szczecin, Poland *

corresponding author: tel. +48-91-449-5891, fax +48-91-449-5891, e-mail address:

[email protected]

Abstract Synthesis and properties of UV-crosslinkable structural adhesives tapes (SATs) based on glycidyl methacrylate, butyl acrylate, 2-hydroxyethyl acrylate and 4-acryloyloxy benzophenone copolymer as well as epoxy resin modified with glass flakes (representing the 1D-type fillers) and a needle-shaped wollastonites (as a 2D-type filler) were described. An influence of fillers introduction into SAT during poly(meth)acrylate binder preparation, on self-adhesive features, curing behaviour (using DSC and FTIR analysis) and overlap shear strength of aluminium/SAT/aluminium joint system have been investigated. Although cohesion values of UV-crosslinked SAT have not vary in case of filler incorporation into tape composition, improved tack as well as higher adhesion to steel for SATs composition containing silane-treated wollastonite have been noted. Structural adhesives tapes with either 1D or 2D-type fillers exhibited lower enthalpy of curing process (in comparison with unfilled sample), while SATs containing glass flakes reached higher temperature of exothermic peak



as well. Additionally, epoxy groups conversion, analyzed during thermal curing (at 140°C), of UV-precured PSAs, was lower for samples containing both types of tested microfillers than for sample of reference tape. In case of short-time thermal curing process (i.e. 15 min, 140°C), the highest overlap shear strength for unfilled structural adhesives tape was noted, while SAT modified with silane-untreated wollastonite exhibited better mechanical properties than other samples cured 30 min at 140°C.

Keywords: Structural adhesive tapes; Epoxy acrylate copolymer; Fillers; UV-crosslinking; Pressure-sensitive adhesives

1. Introduction Structural adhesive tapes (SAT) belong to a new generation of structural adhesives. One- and two-component structural adhesives have been well known for many years, while solid structural adhesives were just described in 1998 [1,2]. Pioneer of the latter products production under the name of “Structural Bonding Tapes”, was the 3M Company. Structural bonding tapes are specific kind of pressure-sensitive adhesive tapes which bond two surfaces together and can be thermally cured to create structural bond. 3M products offer medium adhesion properties and (after curing) high bond strength similar to liquid adhesives. Generally, the structural adhesives may form joints with overlap shear strength in excess of 7 MPa, however in some applications lower bond strength (less than 2 MPa) are required [3]. Structural bonding tapes may be used in a number of applications; SAT are ideal for bonding glass, ceramics and most of metals. In many situations, they can replace screws, rivets, spot welds, liquid adhesives and other permanent fasteners. For example, commercial “Automotive Structural Bonding Tape 9270” (3M, USA) is formulated for bonding the rear view mirror buttons, sensor brackets and other hardware with automotive glass. There are two



main groups of structural bonding tapes: heat-curable and UV-crosslinkable SATs. The former kind of tapes is commonly based on epoxy resins; in some cases acrylics, polyurethanes, phenolics are used [3]. Additionally, commercial SATs always include reinforcement i.e. glass fibers or metal sheets to improve their overlap shear strength [4,5]. That contribution presents the synthesis and properties of novel solid structural adhesives, i.e. structural adhesive tapes characterized with overlap shear strength more than 7 MPa, without reinforcement of tape matrix. Mentioned multicomponent SAT was based on homogenous blend of the new generation UV-crosslinkable epoxy acrylate copolymer, epoxy resin, adhesion promoter as well as latent epoxy-curing agent. Polymeric binder for solid structural adhesives i.e. epoxy acrylate copolymer contained epoxy as well as hydroxyl groups, has been synthesized vie free radical polymerization of glycidyl methacrylate, 2hydroxyethyl acrylate, butyl acrylate and 4-acryloyloxy benzophenone (as UV-crosslinking agent). Additionally, polymerisation process of mentioned monomers, in the presence of either lamellar (1D) or acicular (2D-type) microfillers have been carry out. It is known that fillers may upgrade the mechanical properties as well as affect curing mechanism and the structure of cured epoxy polymers [6]. Mentioned additives are mainly surface-active substances and can act as inhibitors or accelerators with regard to reacting system. On the one hand the surface of additive may catalyse the reaction, on the other hand the reacting molecules can be caught and chemically linked to the surface of filler aggregates (chemisorption). Inhibition effect may also arises from structural hindrance caused by filler particles [7]. In same cases fillers may also induce the formation of different polymer structure domains in adhesive layer - inhomogeneous adhesive layer exhibits fracture resistance, because the ununiform areas of joint act as “crack stoppers” [8].



1. Experimental 1.1. Materials The following chemicals were used to preparation the UV-crosslinkable component of solid structural adhesives: butyl acrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate (BASF, Germany), 4-acryloyloxy benzophenone (ABP; Poly-Chem GmbH, Germany), 2,2’azobis(isobutyronitrile) (AIBN; Merck GmbH, Germany) and ethyl acetate (99%, POCh, Poland) as a solvent. The 1D-type microfillers (glass flakes GF001 and GF007 from Glassflake Ltd., UK) as well as 2D-type microfillers, i.e. wollastonites Vansil HR-325, Vansil HR-1500 (R.T. Vanderbilt Company, Inc., USA) and epoxy silane treated wollastonite Tremin 939-300FST (Quarzwerke GmbH, Germany) have been used. Characteristic of Tab. 1.

applied fillers is shown in Table 1. Bisphenol-A type liquid epoxy resin with epoxy equivalent weight (EEW) 188 g/equiv. and viscosity 12 500 mPa·s (Organika-Sarzyna S.A. in Nowa Sarzyna, Poland) as well as epoxy acrylate oligomer (Ebecryl 860; Cytec GmbH, Germany) were used as a epoxy components of SAT. Additionally, the Lewis acid adduct (Nacure Super Catalyst A 218; Worleé GmbH, Germany) and modified polymethylalkylsiloxane (BYK 325; BYK-Chemie, Germany) have been applied as a latent curing agent and adhesion promoter, respectively. 1.2. Preparation and characterization of UV-crosslinkable epoxy acrylate copolymer The UV-crosslinkable epoxy acrylate copolymer was synthesized via free radical polymerization of butyl acrylate (63 wt%), glycidyl methacrylate (20 wt%), 2-hydroxyethyl acrylate (16 wt%) and 4-acryloyloxy benzophenone (1.0 wt%) in ethyl acetate in the presence of 2,2’-azobis(isobutyronitrile) (0.1 wt. parts/100 wt. parts of comonomers). Polymerization process was carried out for 5 h at 75°C in glass reactor, equipped with mechanical stirrer and oil bath. Monomers and initiator were applied without purification. Epoxy acrylate copolymer



was also prepared in presence of neither glass flakes or wollastonite - microfiller was incorporated (in amount of 10 wt. parts/50 wt. parts of copolymer) into polymerization reactor with monomers. 1.3. Structural adhesive tapes preparation The structural adhesives tapes (SATs) were compounded using epoxy acrylate copolymer (without or with microfiller), epoxy resin (100 wt. parts/100 wt. parts of epoxy acrylate copolymer), epoxy acrylate oligomer (10 wt. parts/100 wt. parts of epoxy acrylate/ epoxy resin composition), latent curing agent (1 wt. parts/100 wt. parts of epoxy acrylate/ epoxy resin composition) as well as adhesion promoter (0.5 wt. parts/100 wt. parts of epoxy acrylate/ epoxy resin composition). Prepared adhesive compositions were applied onto either silicone paper or polyester film (samples for self-adhesive tests), dried for 10 minutes at 105°C and then UV-crosslinked using UV-lamp (Aktiprint-mini 18-2, Technigraf GmbH, Germany). The UV exposition was controlled with integrated radiometer (Dynachem 500, Dynachem Corp., USA); the single UV dose was 900 mJ/cm2. The base weight of the Tab.2. Tab. 2.

adhesive layers was 90 g/m2 and the thickness of SATs was 75 μm. Description of prepared structural adhesive tapes is shown in Table 2 1.4. Self-adhesive tests of SATs Self-adhesive properties such as tack, adhesion to steel and cohesion of prepared SATs were tested according to AFERA standards (Association des Fabricants Européens de Rubans Auto-Adhésifs), i.e. AFERA 4015 (tack), AFERA 4001 (adhesion to steel) and AFERA 4012 (cohesion). Adhesion is defined as the force value required to remove pressure sensitive material from stainless steel plate; the removal is proceed at the angle 180° with speed of 300 mm/min [9]. Tack is characterized by force value required to separate stainless steel plate and adhesive tape applied under low pressure for 0.5 s. Cohesion (i.e. static shear adhesion)



describes the time needed to shear off the adhesive tape sample (under load of 1 kg) from defined steel surface. 1.5. Thermal curing and characterization of SAT joints Thermal curing process of structural adhesive tapes was investigated using differential scanning calorimetry (DSC Q100, TA Instruments, USA) and Fourier Transform Infrared Spectroscopy with attenuated total reflectance (ATR) accessories (Nexus FT-IR, Thermo Nicolet, USA). DSC technique was employed to determine the enthalpy (ΔH) of curing process, the onset temperatures (Ti) and the maximum/peak temperature (Tp) of reactions as well as glass transition temperature (Tg) of UV-crosslinked structural adhesives. Standard aluminum DSC pans were used and the samples (ca. 10 mg) were analyzed from −90°C to 300°C (with heating rate of 10°C/min). Structural adhesive tapes cured 15 and 30 min at 140°C have been analyzed with FTIR; variation of absorbance values at 915cm-1 (oxirane groups), 1150 - 1020 cm-1 (-O- bonds) as well as 3600 - 2500 cm-1 (-OH groups) were observed. Conversion value of epoxy groups (X) was evaluated according to the following equation [10]:  A(t )   ⋅100 (%) X = 1 −  A(0)  where: A(t) - pick surface area corresponding to content of epoxy groups in sample cured for t-time; A(0) – pick surface area corresponding to content of epoxy groups in uncured sample. The overlap shear strength of structural adhesive joints prepared using degreased aluminum panels (PA7, 2 x 25 x 100 mm) and cured either 15 minutes or 30 minutes at 140°C, has been determined according to Polish standard PN-ISO 4587 at room temperature (Instron 4206, Instron USA).



Microscopic images of cured structural adhesives tapes (after mechanical test) were created using 3D Laser Scanning Microscope VK-9700 Keyence, USA. Images of powdered fillers (settled onto glass plate) were prepared, as well. 2. Results and discussion In this study three basic self-adhesive properties (i.e. cohesion, tack and adhesion) were measured. However, cohesion value for all tested UV-crosslinked structural adhesives tapes reached the highest required value (72 hours at RT) the rest investigated features were diversified. Tack and adhesion to steel (Fig. 1) have been depended on a type of used filler; mentioned self-adhesive parameters were depreciated in case of SATs with 1D-type fillers (i.e. glass flakes) as well as SAT filled with silane-untreated wollastonite. In relation to unfilled tape SAT-0 (11.7 N of tack and 11.2 N of adhesion:), the lowest tack value was noted for SAT with glass flakes GF007 (SAT-GF7, 9.9 N) whereas, the composition with Vansil HR-325 wollastonite (SAT-V32; 7.9 N) exhibited the lowest adhesion. In case of SAT containing epoxy silane-treated wollastonite (i.e. Tremin 939 300 FST) both analyzed parameters have been improved; tack values increased to 12.1 N and adhesion to steel reached Fig. 1.

11.9 N. Generally, observed reduction of tack and adhesion to steel values for most SAT/ microfillers tapes may by caused by formation of material structure (during UV-crosslinking process) with lower polymer molecular mobility [11]. In this case decreased mobility of polymer chains decreases wetting of steel. Additionally, the presence of microfiller in polymer matrix may limits the contact area between adhesive coating and substrate. Fillers incorporated into tape compositions, act as dehesive places on their top-layer therefore, adhere surface area is reduced. Nevertheless, in case of SAT with Tremin 939-300FST



wollastonite, neither tack nor adhesion to steel has been depreciated. Probably the thin layer of polymer adhesive binder on the surface of mentioned filler particles (pretreated with epoxy silane) had been created and contact area between structural adhesives tape and substrate wasn’t limited. Differential scanning calorimetry technique has been used to studied the thermal curing process of UV-crosslinked structural adhesives tapes. The DSC thermograms are shown in Fig. 2.; the main characteristic parameters (i.e. enthalpy of curing process, onset temperature and temperature of maximum exothermic peak as well as glass transition temperature) calculated on a basis of mentioned curves are presented in Table 3. Enthalpy value of SAT-0 curing process was 253 J/g, whereas, the total exothermic effects of curing SAT samples containing microfillers were lower and reached values from 195 J/g for SATV35 to 234 J/g for SAT-T. Although the curing initiation temperature (Ti) values for unfilled structural adhesives tape or SATs with microfillers were similar (i.e. 119°C for SAT-0 and 117-121°C for filled tapes), mentioned higher enthalpy value and lower temperature of exothermic peak noted for SAT-0 (i.e. 166°C) show higher thermal reactivity of unfilled composition in comparison with SATs with either glass flakes or wollastonites. In case of tapes with former type of filler, exothermic peaks have been observed at 253-254°C. Moreover, sample with GF001-type glass flakes exhibited lower glass transition temperature value (i.e. −16°C) in comparison with either unfilled SAT (−12°C) or composition with GF007-type glass flakes (−12°C). All tested samples containing wollastonites reached Tg at −13°C. Nevertheless, presented results do not correlate with tack and adhesion data previously presented in Fig. 1. Taking into consideration Tg values, the best self-adhesive features should be observed for mentioned SAT-GF1 composition whereas, that tape exhibited significantly lower tack (10.5 N) as well as lower adhesion to steel (9 N) than



unfilled SAT-0 (11.7 N and 11.2 N) and sample containing epoxy silane-treated wollastonite (SAT-T; 12.1 N and 11.9 N, respectively). Fig. 2. Tab. 3.

FTIR spectrums of structural adhesives tapes (unfilled and filled with glass flakes or wollastonites) cured 15 min at 140°C are presented in Fig. 3. Variation of bands intensity correlated with content of epoxy groups (at 915cm-1; Fig. 4), etheric bonds (in range of 1150 1020 cm-1; Fig. 5) and hydroxyl groups (3600 - 2500 cm-1; Fig. 6) are shown, as well. Heatcuring process of SATs (on a basis of oxirane bands intensity loss) has been analyzed in detail. Conversion values of mentioned groups for all tested SATs heated for 15 min and 30 min at 140°C, are illustrated in Fig. 7. As can be seen, epoxy groups conversion calculated for adhesives modified with both type of fillers, is lower in comparison with unfilled SAT-0. Referenced structural adhesive tape exhibited 84% (15 min) and 93% (30 min) of oxirane group conversion whereas, the most cured SAT with filler (i.e. SAT-GF7) reached only 66% and 68% of conversion, respectively. The lowest value of analyzed parameter was observed for samples containing Vansil HR325 wollastonites (43% after 15 min and 44% after 30 min of heating at 140°C). Generally, FTIR spectroscopy results do not correlate with DSC analysis data (i.e. enthalpy and exothermic peak temperature). Epoxy group conversion slightly depend on average particle size (thickness and aspect ratio) of tested fillers; higher values of former parameter have been observed for GF007 glass flakes and Vansil HR1500 wollastonite. These fillers

Fig. 3. Fig. 4. Fig. 5. Fig. Fig. 6. 3. Fig. Fig. 7. 4. Fig. 5. Fig. 6. Fig. 7.

have larger particles and that feature probably influenced on curing process due to creation of less numerous steric hindrance. UV-crosslinked structural adhesive tape (unfilled and with microfillers) have been used to bond aluminum sheets; created Al/SAT/Al overlap joints were thermal cured either 15 min or 30 min at 140°C. Overlap shear strength values of prepared joints are presented in Fig.



8. The highest mechanical properties (i.e. 13.3 MPa) was noted for unfilled SAT sample cured 15 min at 140°C. Analyzed parameter has been deteriorated in case of either heating of SAT for 30 min (7.2 MPa) or incorporation of fillers into structural adhesives tape composition. Almost all tested samples filled with glass flakes or wollastonites, revealed more than 7 MPa overlap shear strength; only SAT-GF7 tape reached slightly lower value (i.e. 6.9 MPa) than value required for structural-type adhesive composition. However, the results of the analyzed feature for SATs containing fillers are lower (in range of 34-48% according to unfilled SAT-0 cured 15 min), SAT-V15 reached higher overlap shear strength (8.2 MPa) than mentioned reference sample cured 30 min at 140°C (7.3 MPa). It should be pointed that overlap shear strength of joints based on SAT-V15 as well as SAT-GF1 or SAT-V32, do not significantly depend on curing time (at 140°C). Taking into consideration results of mechanical tests of Al/SAT/Al joints and calculated values of epoxy groups conversion after tape heating for 15 and 30 min at 140°C, it should be claimed that higher epoxy group conversion (oxirane rings loss, higher curing degree) reduce overlap shear strength. Nevertheless, the former parameter value does not directly correspond with the latter feature; e.g. overlap shear strength of SAT-0 tape reached 13.3 MPa (at 84% of epoxy group conversion) and 7.3 MPa (at 93%) while sample filled with Vansil HR323 wollastonite exhibited 7.3 MPa of overlap shear strength at 43 % and 6.7 MPa Fig. 8.

at 44% of epoxy group conversion, respectively. Images of thermal-cured SAT bonds (after overlap shear strength tests) as well as images of tested 1D and 2D-type microfillers, prepared using laser scanning microscope are shown in Fig. 9. Incorporated fillers are quite well visible in cured adhesives and no significantly cracks (i.e. delamination between polymer binder and filler) during strength test

Fig. 9.



have been occurred. Additionally, it should be pointed that analyzed fillers were uniformly dispersed in SAT bonds (particle sedimentation was not observed). 3. Conclusions In this study the new developed structural adhesive tape has been characterized. Modification of mentioned solid structural adhesive using either 1D or 2D-type microfillers (on the stage of epoxy acrylate copolymer synthesis) significantly influences on principal properties of prepared product, i.e. self-adhesive features (tack and adhesion to steel), thermal-curing behaviour (conversion of epoxy groups) as well as overlap shear strength of aluminium/SAT/aluminium joints. Probably, analyzed parameters value mainly depend on structural hindrance created by microfiller particles in polymer matrix. However, the most strength joints (after curing for 15 min at 140°C) have been obtained using unfilled structural adhesive tape (SAT-0), in case of longer thermal-curing process the best mechanical properties have been noted for joints with SAT modified with Vansil HR1500 wollastonite.

Acknowledgment This research was financial supported by a grants from the Foundation for Polish Science (VENTURES and START Programmes). The authors would like to thank Mrs Katarzyna Wilpiszewska (Polymer Institute, West Pomeranian University of Technology in Szczecin) for LSM images preparation.



References [1] Brockmann W, Geiss P, Klingen J, Schröder B. Adhesive Bonding. Materials, Applications and Technology. Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA; 2009. [2] Weglewski J, Pastirik D. Patent WO 02/079337; 2002. [3] Sikkel B, Brandys F, Chen P-J. Patent WO 2005/073330; 2005. [4] Weglewski J, Dennis C. Patent US 2002/0182955; 2002. [5] Sikkel B. Patent EP 1,557,449; 2004. [6] Prime R, Turi E. Thermal Characterization of Polymeric Materials. New York: Academic Press; 1981. [7] Harsch M, Karger-Kocsis J, Holst M. Influence of fillers and additives on the cure kinetics of an epoxy/anhydride resin. Eur Polym J 2007;43:1168-78. [8] Brockmann W, Geiss P, Klingen J, Schröder B. Adhesive Bonding. Materials, Applications and Technology. Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA; 2009. [9] Czech Z. Vernetzung von Haftklebstoffen auf Polyacrylatbasis. Szczecin: WUPS; 1999. [10] Cullinane S, Cullinane K, Lachenal G, Pierre A, Poisson N. FT-NIR spectroscopy: trends and application to the kinetic study of epoxy/triamine system (comparison with DSC and SEC results). Micron 1996;27:329-34. [11] Kajtna J, Krajnic M. UV crosslinkable microsphere pressure-sensitive adhesivesinfluence on adhesive properties. Int J Adhes Adhes 2011;31:29-35.



Table 1. Fillers specification

Filler name

Particle shape

Particle thickness (μm)

Aspect ratio 1

Oil absorption (g/100g)

Density (g/cm3)

GF001

Lamellar

1.0 -1.3

1 : 150

—

2.6

GF007

Lamellar

5.5 - 10

1 : 27

—

2.6

Vansil HR1500

Acicular

2,4 - 12

1 : 14

44

2.9

Vansil HR325

Acicular

0,5 - 3

1 : 12

40

2.9

Acicular

1.0 - 9.0

1:6

40

2.85

Tremin 939-300FST 1- maximum value

Table 2. Structural adhesives tape compositions containing various microfillers

SAT acronym

Filler acronym

SAT-0

—

SAT-GF1

GF001

SAT-GF7

GF007

SAT-V15

Vansil HR1500

SAT-V32

Vansil HR325

SAT-T

Tremin 939-300FST

Component A (wt. parts) Epoxy acrylate Filler copolymer

Epoxy resin

Component B (wt. parts) Epoxy Curing Adhesion acrylate agent promoter oligomer

0

50

10

50

10

1

0.5



Table 3. Thermal properties of UV-crosslinked structural adhesive tapes SAT acronym

Enthalpy, ∆H (J/g)

Onset temperature, Ti (°C)

Max. exothermic peak temperature, Tp (°C)

Glass transition temperature, Tg (°C)

SAT-0

253

119

166

-12

SAT-GF1

208

121

254

-16

SAT-GF7

215

120

253

-12

SAT-V15

211

117

187

-13

SAT-V32

195

119

196

-13

SAT-T

234

120

188

-13

tack adhesion

Tack / Adhesion (N)

12

10

8

6 SAT-0

SAT-GF1

SAT-GF7

SAT-V15

SAT-V32

SAT-T

Structural adhesive tape

Fig.1. Tack and adhesion to steel for UV-crosslinked structural adhesive tapes



Heat flow (W/g)

SAT-T SAT-V32 SAT-V15 SAT-GF7 SAT-GF1 SAT-0

-50

0

50

100

150

200

250

300

o

Temperature ( C)

Fig. 2. DSC thermograms of UV-crosslinked structural adhesive tapes

Absorbance (units)


4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber (cm )

Fig. 3. FTIR spectra of structural adhesives tapes cured 15 min at 140°C



SAT-V32 SAT-GF1

SAT-T SAT-GF7

Absorbance (units)

SAT-V15 SAT-0

950

940

930

920

910

900

890

880

870

860

850

-1

Wavenumber (cm )

Fig. 4. FTIR spectra (in range of epoxy groups absorbance) of structural adhesives tapes cured 15 min at 140°C

Absorbance (units)


1500

1400

1300

1200

1100

1000

-1

Wavenumber (cm )

Fig. 5. FTIR spectra (in range of etheric bond absorbance) of structural adhesives tapes cured 15 min at 140°C



Absorbance (units)


4000

3750

3500

3250

3000

2750

2500

-1

Wavenumber (cm )

Fig. 6. FTIR spectra (in range of hydroxyl groups absorbance) of structural adhesives tapes cured 15 min at 140°C

0

140 C/15 min 0 140 C/30 min

90

Conversion (%)

80

70

60

50

40 SAT-0

SAT-GF1

SAT-GF7

SAT-V15

SAT-V32

SAT-T


Fig. 7. Epoxy groups conversion of structural adhesive tapes cured 15 min and 30 min at 140°C



14

0

140 C/15 min 0 140 C/30 min

Overlap shear strenght (MPa)

12

10 8

6

4

2

0 SAT-0

SAT-GF1

SAT-GF7

SAT-V15

SAT-V32

SAT-T


Fig. 8. Overlap share strength values for aluminum/SAT/aluminum joints cured 15 min and 30 min at 140°C



Fig. 9. LSM images of fillers and cured SAT joints containing various fillers