Article GM-Improved Antiaging Effect of Acrylonitrile Butadiene Styrene in Different Thermal Environments

Yuchao Wang 1,2, Ming Chen 1, Miaoyu Lan 1, Zhi Li 1, Shulai Lu 1,* and Guangfeng Wu 2,*

1 ABS Technology Center of PetroChina, Jilin 132021, China; [email protected] (Y.W.); [email protected] (M.C.); [email protected] (M.L.); [email protected] (Z.L.) 2 School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China * Correspondence: [email protected] (S.L.); [email protected] (G.W.)

 Received: 16 November 2019; Accepted: 20 December 2019; Published: 28 December 2019 

Abstract: A stabilizer called 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (GM) was mixed in acrylonitrile butadiene styrene (ABS) with the same amount of 9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (DSPDP), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076) and tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (Irganox 3114) to investigate the influence of additives on the antiaging effect of ABS in oven aging or repeated extrusion aging. It was found that the ABS doped with the GM stabilizer showed a better yellowing resistance and thermal stability than the ABS doped with other . Owing to the fact that the stabilizer can act on the free radicals before it has been peroxidized, it could trap the free radicals as a consequence of directly blocking the oxidation process of the active species, thus solving the problem of oxidative degradation of the materials from the source. This work provides guidance for improving thermal stability of ABS, indicating a promising potential for industrial application.

Keywords: degradation; acrylonitrile butadiene styrene; convection oven; extrusion; recycling; mechanical properties

1. Introduction Acrylonitrile butadiene styrene (ABS) resins have attracted considerable attention due to their superior mechanical properties [1], heat resistance [2], chemical resistance [3], recyclability [4–6] and ease of processing [7,8], and are widely used in telecommunications, automotive industry, consumer markets and business machines [9,10]. However, ABS is easily excited by the heat [11,12], light [13–15], oxygen [16,17] and other conditions during its processing [18,19], leading to aging degradations of the material. Because the presence of unstable carbon–carbon double bonds in the butadiene microstructure generates macromolecular-active radicals during processing, thermal degradation is promoted and results in a rapid yellowing and brittleness of ABS [20,21]. To solve this problem, most of previous reports employed doping strategy to prepare highly aging-resistant ABS resins. Some people chose traditional additives to improve heat resistance. For example, Fiorio’s group found that the addition of primary antioxidants in ABS increases the thermal–oxidative stability, whereas the secondary antioxidants only increase the oxidation peak temperature [22]. Others have chosen new types of additives. Ong’s group showed that pretreatments on filled oil palm fiber can lower the onset thermal degradation temperature of acrylonitrile butadiene styrene composites in differential thermogravimetric analysis [23]. Teh’s group successfully improved

Polymers 2020, 12, 46; doi:10.3390/polym12010046 www.mdpi.com/journal/polymers Polymers 2020, 12, 46 2 of 10 the thermal stability of the ABS resin by adding carbon black (CB) to the ABS [24]. Yan’s group enhanced the electrical conductivity and thermal conductivity of the ABS via the addition of reduced graphene oxide (rGO) in the ABS resin, because it can tightly wrap the rGO sheet on the surface of ABS microspheres [25]. In addition, Allen’s group used other stabilizers to conduct a comprehensive study of K-resin by both thermal-aging degradation and photo-aging degradation [26]. However, the doping strategy also brings about changes in the color-phase morphology or other properties thereof. This dilemma makes it difficult to explore the improved thermal stability for the ABS resin [27]. Here, we successfully obtained high thermal stability ABS through a doping strategy without affecting the properties of ABS itself. A systematic study was carried out to investigate effects of 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (GM), 9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (DSPDP), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076) and tris(3,5-di- tert-butyl-4-hydroxybenzyl) isocyanurate (Irganox 3114) antioxidants on the thermal aging of ABS in two different thermal environments, a 100 ◦C convection oven and a 240 ◦C extruder simulating the extreme environment. It was found that the ABS doped with the GM stabilizer showed better yellowing resistance and thermal stability than the ABS doped with other antioxidants. Owing to the fact that the stabilizer can act on the free radicals before it has been peroxidized, it could trap the free radicals as a consequence of directly blocking the oxidation process of the active species, thus solving the problem of oxidative degradation of the materials from the source. Hence, the GM can greatly improve thermal stability of the ABS in the convection oven or the extruder. This work provides guidance for improving thermal stability of ABS, indicating promising potential for industrial application.

2. Materials and Methods

2.1. Materials The materials used in this study were as follows: ABS-grafted powder PW-151 (KunLun, Jilin, China, obtained by emulsion polymerization), SAN resin 2437 (KunLun, Jilin, China), acrylic acid (Sigma Aldrich, Shanghai, China), phosphoryl trichloride (Sigma Aldrich, Shanghai, China), triethylamine (TEAE), 2,2’-methylenebis(6-tert-butyl-4-methylphenol) (Antioxidant 2246, Sigma Aldrich, Shanghai, China), GM (laboratory homemade), DSPDP (Cytec, Jilin, China, phosphite secondary antioxidant), Irganox 1076 (BASF, Shanghai, China, phenolic primary antioxidant) and Irganox 3114 (BASF, Shanghai, China, antioxidant-stabilizer).

2.2. Synthesis of Stabilizer GM Firstly, 120 g of Antioxidant 2246, 20 g of acrylic acid, 2.0 g of triethylamine and an appropriate amount of the organic solvent were sequentially added to a 1000 mL four-necked flask. After heating in an oil bath under stirring, the temperature was raised to about 110 ◦C and 30 g of phosphoryl trichloride were added dropwise; the dropwise addition was completed in 45 min. The dropped raw material reacted to release a small amount of hydrogen chloride gas which was absorbed by the hydrogen chloride absorber. The temperature was maintained for 3 h before the reaction was completed. Thereafter, the organic solvent recrystallization method was used to purify the crude reaction product. Finally, a yellowish crystalline product was obtained which is referred to as Stabilizer GM. We use the synthetic method in the article by Yachigo’s group to obtain the uniform-quality stabilizer GM from the raw materials, so as to obtain reliable and repeatable experimental results [28].

2.3. Sample Preparation The ABS grafted powder and the SAN resin were mixed at a mass ratio of 25:75, and four equal parts of the GM, DSPDP, Irganox 1076 and Irganox 3114 were added in in the mixture, then sheared and granulated the mixture by a twin-screw extruder at 240 ◦C. The granulated ABS-material was subjected Polymers 2020, 12, 46 3 of 10

to a series of eight cycles of oven aging at 100 ◦C for 72 h per cycle, or five cycles of anaerobic repeated extrusion at 240 ◦C. We chose the temperature at 100 and 240 ◦C was because these temperatures presented greater challenge for the additives to maintain the same performance of the materials. In addition, it was more intuitively to compare the differences of each additives in the protective ability [6,29–32].

2.4. Analysis

2.4.1. Fourier Transform (FTIR) Fourier transform infrared spectroscopy (FTIR, IR Prestige-21, Shimadz, Kyoto, Japan) was used to evaluate the four additives and changes in ABS samples through accelerated degradation. All samples 1 were studied in attenuated total reflectance (ATR) mode from 4000 to 600 cm− . The spectra of ABS 1 samples form an absorbance peak of carbonyl at 1720 cm− during degradation, which was compared 1 to the absorbance peak of acrylonitrile at 2237 cm− . The integral ratio between the absorbance peak 1 1 at 1720 cm− (carbonyl) and that at 2237 cm− (acrylonitrile) was defined as the carbonyl index, the equation is as follows [33–35]:

Transmittance at 1720 cm 1 Carbonyl index = − . (1) 1 Transmittance at 2237 cm− 2.4.2. Thermogravimetric Analysis (TGA) All raw materials were characterized simultaneously by thermogravimetric analysis (STA 449 F5, Netzsch, Selb, Germany). Samples (for the results, see Figure S1) of 10 2 mg were heated from 25 to 1 ± 600 ◦C at a heating rate of 10 ◦C min− in a Pt–Rh pan [36]. The shielding gas was high-purity nitrogen and the flow rate set to 20 mL min 1. The purge gas was air and the flow rate set to 20 mL min 1. · − · − 2.4.3. Color Measurements The color properties of the samples were investigated with a spectrophotometer (UltraScan PRO, Hunterlab, Reston, VA, USA) using a Artificial Daylight 6500K (D65) light source and 10◦ viewing angle. All color measurements were obtained from the compression molded films. The color difference (∆E) between the two sets of injection samples was tested. One was that the temperature of the cutting section of the cylinder was 220 ◦C and the residence time of the cylinder 40 s. The other was that the temperature of the cutting section of the plastic cylinder was 250 ◦C and the residence time 180 s. The difference between the heat resistance of the ABS resin additives was characterized by testing the color difference values of ABS samples under these two conditions. The results show three colorimetric coordinates: luminosity (L), red/green component (a) and blue/yellow component (b). The total color difference (∆E) between the samples caused by temperature or time change was calculated using Equations (2) and (3) [35]: p ∆E = ∆L2 + ∆a2 + ∆b2 (2)

∆L = L L , ∆a = a a , ∆b = b b , (3) 250°C − 220°C 250°C − 220°C 250°C − 220°C where ∆L is the difference of the injection-molded-samples between 250 ◦C and 220 ◦C, ∆a is red/green component difference between the samples under the two different temperatures and ∆b is the difference of the blue/yellow component. The yellowing index (YI) was obtained by the International Commission on illumination (CIE) tristimulus values X, Y and Z according to the CIELAB color system [37]. The YI was determined according to Equation (4) [22]:

100 (1.3013X 1.1498Z) YI = × − . (4) Y Polymers 2020, 12, 46 4 of 10

Polymers 2019, 11, x FOR PEER REVIEW 4 of 10 2.4.4. Mechanical Testing Notched-impact strength and melt-index rate (MFR) were measured according to ASTM-D256 Notched-impact strength and melt-index rate (MFR) were measured according to ASTM-D256 and ASTM-D1238 standards, respectively. and ASTM-D1238 standards, respectively.

3. Results

3.1. Additive Selection To systematically study study and and understand understand the the influenc influencee of additives of additives on the on antiaging the antiaging effect e offfect ABS, of ABS,the additives the additives GM, GM,DSPDP, DSPDP, Irganox Irganox 1076 1076 and and Irgano Irganoxx 3114 3114 were were selected selected to to dope dope the the ABS. The molecular structure of the additivesadditives is shownshown inin FigureFigure1 1a.a. FigureFigure1 b1b shows shows the the Fourier Fourier transform transform infrared spectroscopyspectroscopy of of the the additives. additives. In ourIn our experiment, experiment, we synthesizedwe synthesize thed stabilizer the stabilizer GM. As GM. shown As 1 −1 inshown Figure in1 b,Figure 804 and 1b, 856804 cmand− 856are cm the bending are the vibrationbending vibration peaks of thepeaks benzene of the ring; benzene the stretching ring; the 1 −1 vibrationstretching peak vibration of the peak benzene of the appears benzene at appears 1599 cm at− 1599, which cm proves, which that proves the synthesized that the synthesized GM material GM 1 −1 doesmaterial contain does the contain benzene the ring benzene group. ring The group. –OH bendingThe –OH vibration bending peak vibration appears peak at 1358appears cm− at, indicating1358 cm , thatindicating the synthesized that the synthesized GM material GM contains material the contai phenolicns the hydroxyl phenolic functional hydroxyl group. functional In addition, group. the In 1 −1 1161,addition, 1633 the and 1161, 1729 1633 cm− andpeaks 1729 are cm C–O, peaks C= Care and C–O, C= OC=C stretching and C=O vibration stretching peaks, vibration respectively, peaks, indicatingrespectively, that indicating the microscopic that the benzene microscopic ring structurebenzene ring of the structure sample of is attachedthe sample with is attached an acrylic with group. an Inacrylic summary, group. the In preparedsummary, material the prepared is a desired material GM is product a desired containing GM product a bisphenol containing acryloyl a bisphenol group. Figureacryloyl1b group. also shows Figure the 1b Fourier also shows transform the Fourier infrared transform spectroscopy infrared of DSPDP, spectros Irganoxcopy of 1076 DSPDP, and IrganoxIrganox 3114,1076 and three Irganox other additives, 3114, three showing other additives, POC, Ar–OH showing and =POC,CH, threeAr–OH characteristic and =CH, three functional characteristic groups 1 −1 appearingfunctional atgroups 1032, appearing 3638 and 852 at 1032, cm− .3638 and 852 cm .

Figure 1.1. ((aa)) Molecular Molecular structure of didifferentfferent additives;additives; 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5- methylbenzyl)-4-methylphenyl acrylate (GM),(GM), 9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9- diphosphaspiro[5.5]undecane (DSPDP), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox(Irganox 1076)1076) andand tris(3,5-di-tert-butyl-4-hydroxybenzyl)tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (Irganox 3114).3114). (b) FourierFourier transform infraredinfrared spectroscopyspectroscopy ofof thethe additives.additives. The four kinds of additives we selected play different roles in the thermal-oxidation process. The The four kinds of additives we selected play different roles in the thermal-oxidation process. The GM stabilization mechanism is confirmed to be a unique bifunctional mechanism, which consists GM stabilization mechanism is confirmed to be a unique bifunctional mechanism, which consists of of polymer trapping by the acrylate group, followed by rapid hydrogen transfer from polymer radical trapping by the acrylate group, followed by rapid hydrogen transfer from intramolecular hydrogen-bonded phenolic hydroxyl groups to form stable phenoxyl radicals. Therefore, intramolecular hydrogen-bonded phenolic hydroxyl groups to form stable phenoxyl radicals. the problem of oxidative degradation of materials is solved from the source of the thermal-oxidation Therefore, the problem of oxidative degradation of materials is solved from the source of the thermal- process (for the schematic, see Figure S2). DSPDP acts as a scavenger that rapidly oxidation process (for the schematic, see Figure S2). DSPDP acts as a hydroperoxide scavenger that rapidly decomposes macromolecular hydrogen peroxide, stopping the thermal-oxidation process and thus preventing continued aging. Irganox 1076 and Irganox 3114 act as radical scavengers that

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Polymers 2019, 11, x FOR PEER REVIEW 5 of 10 decomposes macromolecular hydrogen peroxide, stopping the thermal-oxidation process and thus preventing continued aging. Irganox 1076 and Irganox 3114 act as radical scavengers that react with react with macromolecular peroxidative free radicals to inhibit the partial thermal-oxidation process macromolecular peroxidative free radicals to inhibit the partial thermal-oxidation process and hence and hence slows aging. It can be confirmed that GM has a unique heat-resistant effect compared with slows aging. It can be confirmed that GM has a unique heat-resistant effect compared with traditional traditional primary and secondary antioxidants. primary and secondary antioxidants. 3.2. Carbonyl Index 3.2. Carbonyl Index To explore the influence of additives on the antiaging effect of ABS, we calculated the carbonyl To explore the influence of additives on the antiaging effect of ABS, we calculated the carbonyl index (CI) of ABS with different additives. The carbonyl index is defined as the integral ratio because index (CI) of ABS with different additives. The carbonyl index is defined as the integral ratio because the absorbance peaks of acryloacrylonitrile are usually unchanged during degradation progress. The the absorbance peaks of acryloacrylonitrile are usually unchanged during degradation progress. The oxidation of the rubber phase of ABS material would form carbonyl groups in the oxidation of the polybutadiene rubber phase of ABS material would form carbonyl groups in the degradation, so that the degradation of the material can be evaluated from the change of the carbonyl degradation, so that the degradation of the material can be evaluated from the change of the carbonyl absorption peak. The Fourier transform infrared spectroscopy of ABS with different additives after absorption peak. The Fourier transform infrared spectroscopy of ABS with different additives after eight cycles in the oven aging at 100 °C for 72 h is shown in Figure 2a. Figure 2b shows the dependence eight cycles in the oven aging at 100 ◦C for 72 h is shown in Figure2a. Figure2b shows the dependence of carbonyl index for ABS with different additives on the number of cycles in the oven aging at 100 of carbonyl index for ABS with different additives on the number of cycles in the oven aging at 100 ◦C °C for 72 h. It can be clearly observed that the carbonyl index value of ABS with the GM is the lowest, for 72 h. It can be clearly observed that the carbonyl index value of ABS with the GM is the lowest, only only 0.68, which is much smaller than that of ABS with DSPDP, Irganox 1076 and Irganox 3114. This 0.68, which is much smaller than that of ABS with DSPDP, Irganox 1076 and Irganox 3114. This result result indicated that the ABS with the GM exhibited the least aging, and the additive of GM indicated that the ABS with the GM exhibited the least aging, and the additive of GM successfully successfully improved the antiaging effect of ABS. It is confirmed that the effect of the GM additive, improved the antiaging effect of ABS. It is confirmed that the effect of the GM additive, which solves which solves the problem of oxidative degradation of materials from the source of the thermal- the problem of oxidative degradation of materials from the source of the thermal-oxidation process, oxidation process, and is stronger than that of the additive of DSPDP (hydroperoxide scavenger), and is stronger than that of the additive of DSPDP (hydroperoxide scavenger), Irganox 1076 or Irganox Irganox 1076 or Irganox 3114 (radical scavengers). 3114 (radical scavengers).

Figure 2. (a) Fourier transform infrared spectroscopy (FTIR) of acrylonitrile butadiene styrene (ABS) Figure 2. (a) Fourier transform infrared spectroscopy (FTIR) of acrylonitrile butadiene styrene (ABS) with different additives after eight cycles at 100 ◦C. (b) Carbonyl index versus aging cycles for ABS with different additives after eight cycles at 100 °C. (b) Carbonyl index versus aging cycles for ABS with different additives at 100 ◦C. with different additives at 100 °C. 3.3. Thermal Properties 3.3. Thermal Properties To further explore the influence of additives on the antiaging effect of ABS, we evaluated the temperatureTo further of ABSexplore with the di ffinfluenceerent additives of additives under on di fftheerent antiaging weight losseffect in of the ABS, two we diff evaluatederent thermal the temperatureenvironments. of FigureABS with3 shows different the temperatureadditives under from di thermogravimetricfferent weight loss in analysis the two (TGA) different of di thermalfferent weightenvironments. loss for ABSFigure with 3 shows different the additives temperature after from eight thermogravimetric cycles in the oven aging analysis at 100 (TGA)◦C for of 72different h. The weightinitial 1% loss decomposition for ABS with temperaturedifferent additives (T1%) ofafter ABS eight with cycles different in the additives oven aging in the at convection100 °C for oven72 h. Theis shown initial in 1% Figure decomposition3a. It can be temperature observed that (T1% the) of initial ABS decompositionwith different additives temperatures in the of convection ABS with ovenGM, DSPDP,is shown Irganox in Figure 1076 3a. and It Irganoxcan be observed 3114 all show that athe tendency initial decomposition to decrease first temperatures and then increase of ABS as withthe number GM, DSPDP, of aging Irganox cycles increased.1076 and Irganox The temperature 3114 all show drop isa duetendency to the to partial decrease aging first of theand added then increasechemicals asin the the number aerobic of environment aging cycles duringincreased. the The first temperature three cycles. drop When is due the sampleto the partial was placed aging of in the thermogravimetricadded chemicals in analyzerthe aerobic with environment similar high duri temperature,ng the first the three added cycles. group When was the oxidized sample prior was placedto the ABS in the sample, thermogravimetric which lowered analyzer the overall with initial similarT1% decompositionhigh temperature, temperature. the added The groupT1% rosewas oxidizedafter 3–5 cyclesprior to because the ABS the sample, addition which of antioxidant lowered the was overall almost initial oxidized T1% anddecomposition could no longer temperature. affect the Thedecomposition T1% rose after temperature 3–5 cycles ofbecause the ABS the resin. addition Moreover, of antioxidant the 1% mass was decompositionalmost oxidized temperature and could no of ABSlonger with affect GM the and decomposition DSPDP is almost temperature higher than of th thate ABS of ABS resin. with Moreover, Irganox the 1076 1% and mass Irganox decomposition 3114. This phenomenontemperature of also ABS appears with GM for andT3% DSPDPand T5% is, shownalmost inhigher Figure than3b,c, that which of ABS indicates with Irganox that the 1076 acrylate and Irganox 3114. This phenomenon also appears for T3% and T5%, shown in Figure 3b,c, which indicates that the acrylate functional group, unique to GM, and the phosphite structure contained in DSPDP play an important role in resistance to the thermal–oxidative degradation of polymers.

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functional group, unique to GM, and the phosphite structure contained in DSPDP play an important PolymersPolymers 20192019,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 66 ofof 1010 role in resistance to the thermal–oxidative degradation of polymers.

Figure 3. (a) Temperature of 1% weight loss for ABS with different additives; (b) temperature of 3% FigureFigureweight 3.3. loss ((aa)) Temperature forTemperature ABS with ofof di 1%ff1%erent weightweight additives; lossloss forfor and ABSABS ( c withwith) temperature differentdifferent additives;additives; of 5% weight ((bb)) temperaturetemperature loss for ABS ofof with 3%3% weightweightdifferent lossloss additives. forfor ABSABS withwith differentdifferent additives;additives; andand ((cc)) temperaturetemperature ofof 5%5% weightweight lossloss forfor ABSABS withwith differentdifferent additives.additives. In addition, dependence of the initial temperature on the weight loss for ABS with different additivesInIn addition,addition, after extrusion dependencedependence steps isofof shown thethe initialinitial in Figure temperattemperat4. Duringureure onon the thethe extrusion weightweight process, lossloss forfor it ABSABS is easy withwith to produce differentdifferent a additivesadditiveshigh temperature afterafter extrusionextrusion and anoxic stepssteps environment isis shownshown inin FigureFigure when the 4.4. DuringDuring material thethe is extrusionextrusion filled between process,process, the it screwit isis easyeasy and toto the produceproduce barrel. aaFigure highhigh 4temperaturetemperaturea shows the initialandand anoxicanoxic degradation environmentenvironment temperature whenwhen of thethe ABS materialmaterial with di isisff filledfillederent additivesbetweenbetween thethe after screwscrew one extrusion andand thethe barrel.barrel.process. FigureFigure It can 4a4a be showsshows seen that thethe theinitialinitial thermal degradationdegradation decomposition temptemperatureerature temperature ofof ABSABS withwith of ABS diffdiff witherenterent GM, additivesadditives DSPDP, afterafter Irganox oneone extrusionextrusion1076 and Irganoxprocess.process. 3114 ItIt cancan are be approximatelybe seenseen thatthat thethe the thth same,ermalermal and decompositiondecomposition as the percentage temperaturetemperature of weight ofof loss ABSABS increased, withwith GM,GM, the DSPDP,DSPDP,trend of IrganoxIrganox thermal 10761076 decomposition andand IrganoxIrganox temperature 31143114 areare approximatapproximat remainedelyely consistent. thethe same,same, As andand the asas number thethe percentagepercentage of cycles ofof increased weightweight losslossto three increased,increased, (Figure thethe4b), trendtrend the thermal ofof thermalthermal decomposition decompositiondecomposition temperature temperaturetemperature of ABS remainedremained with GM consistent.consistent. was higher AsAs the thanthe numbernumber that of ofofABS cyclescycles with increasedincreased other additives. toto threethree This (Figure(Figure is because 4b),4b), thethe the therther acrylatemalmal decompositiondecomposition structure of bisphenol temperaturetemperature monoacrylate ofof ABSABS withwith can GMGM quickly waswas higherhighercapture thanthan macromolecule thatthat ofof ABSABS free withwith radicals otherother at additives.additives. the initial ThTh stageisis isis (Equation becausebecause (5)),thethe acrylate thusacrylate preventing structurestructure macromolecules ofof bisphenolbisphenol monoacrylatemonoacrylatefrom self-crosslinking cancan quicklyquickly (Equation capturecapture (6)). macromoleculemacromolecule The special bisphenol freefree radicalsradicals monoacrylate atat thethe initialinitial generates stagestage (Equation(Equation a relatively (5)),(5)), stable thusthus preventingpreventingradical ending macromoleculesmacromolecules reaction. As shown frfromom in self-crosslinkingself-crosslinking Figure4c,d, the stabilizer (Equatio(Equatio GMnn (6)). can(6)). similarlyTheThe specialspecial increase bisphenolbisphenol the heat monoacrylatemonoacrylateresistance of the generatesgenerates ABS sample aa relativelyrelatively after 5–6 stablestable extrusions. radicalradical endingending reaction.reaction. AsAs shownshown inin FigureFigure 4c,d,4c,d, thethe stabilizerstabilizer GMGM cancan similarlysimilarly increaseincrease thethe heatheat reresistancesistance ofof thethe ABSABS samplesample afterafter 5–65–6 extrusions.extrusions. R + ln H RH + ln (5) R•R•• ++ lnln HH →→→ RH RH ++ ln•ln• • (5) (5) 2R2R• →→ R–R (6) (6) 2R•• → R–R (6) wherewhere R•R• R representsrepresents macromolecule macromolecule freefree radicals,radiradicals,cals, RHRH representsrepresents stablestablestable macromolecule.macromolecule.macromolecule. •

Figure 4. Dependence of the initial temperature on the weight loss for ABS with different additives FigureFigureafter di 4.4.ff erent DependenceDependence extrusion ofof times: thethe initialinitial (a) the temperaturetemperature first extrusion; onon thethe (b) weight theweight third lossloss extrusion; forfor ABSABS ( cwithwith) the differentdifferent fifth extrusion; additivesadditives and afterafter(d) the differentdifferent sixth extrusion. extrusionextrusion times:times: ((aa)) thethe firstfirst extrusion;extrusion; ((bb)) thethe thirdthird extrusion;extrusion; ((cc)) thethe fifthfifth extrusion;extrusion; andand ((dd)) thethe sixthsixth extrusion.extrusion.

3.4.3.4. OpticalOptical andand MechanicalMechanical PropertiesProperties LastLast butbut notnot least,least, wewe alsoalso exploredexplored thethe influenceinfluence ofof additivesadditives onon thethe opticaloptical andand mechanicalmechanical propertiesproperties ofof ABSABS inin twotwo differentdifferent thermalthermal envienvironments.ronments. FiguresFigures 55 andand 66 showshow thethe opticaloptical andand

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Polymers3.4. 2019 Optical, 11, x andFOR Mechanical PEER REVIEW Properties 7 of 10 Last but not least, we also explored the influence of additives on the optical and mechanical mechanical properties of ABS with different additives after aging within the convection oven and the properties of ABS in two different thermal environments. Figures5 and6 show the optical and extruder. The additive of GM not only improved the thermal stability of ABS, but it also had a good mechanical properties of ABS with different additives after aging within the convection oven and the colorextruder. promotion The in additive the two of different GM not only thermal improved environm the thermalents. As stability shown of in ABS, Figures but it 5a also and had 6a, a goodit can be observedcolor that promotion the ABS in with the two different different additives thermal environments.yellowed after As oven shown aging in Figures or repeated5a and extrusion6a, it can be aging. The yellowobserved index that theof ABS withwith di difffferenterent additives additives yellowed increased after ovenas well aging as orthe repeated color difference extrusion aging. given in FiguresThe 5b yellow and 6b. index of ABS with different additives increased as well as the color difference given in AccordingFigures5b and to 6theb. Equation (7), and further combining the yellow index with the color difference index, theAccording phosphite to the group Equation contained (7), and furtherin the combining ABS with the yellowDSPDP index reacts with faster the color to di decomposefference hydroperoxideindex, the phosphite when compared group contained to other in thesamples: ABS with DSPDP reacts faster to decompose hydroperoxide when compared to other samples: ROOH + 2(R’O)3POH → 2(R’O)3P=O + ROH + H2O. (7) ROOH + 2(R0O)3POH 2(R0O) P=O + ROH + H O (7) where R repersents the alkyl group in macromolec→ ular, R’3 repersents the alkyl2 group in DSPDP Thewhere increase R repersents of color the alkylstability group of in ABS macromolecular, with Irganox R’ repersents1076 indicates the alkyl that group the hindered in DSPDP. phenolic antioxidantThe easily increase forms of color anthraquinone stability of ABSafter with absorb Irganoxing the 1076 peroxy indicates radical, that the causing hindered the phenolic material to turn yellow.antioxidant easily forms anthraquinone after absorbing the peroxy radical, causing the material to Furthermore,turn yellow. a cantilever-beam impact tester was used to analyze the notched impact strength (IZOD) ofFurthermore, ABS with different a cantilever-beam additives impactafter aging tester by was the used convection to analyze oven the or notched the extruder. impact strength In addition, the molecular(IZOD) of ABSmobility with diofff erentABS additiveswith different after aging additives by the convectionwas analyzed oven using or the extruder.a melt-flow In addition, tester. The notchedthe molecularimpact strength mobility of of ABS ABS with with different different additivesadditives was is shown analyzed in Figures using a melt-flow5c and 6c, tester. and the The melt notched impact strength of ABS with different additives is shown in Figures5c and6c, and the melt flow rate (MFR) is shown in Figures 5d and 6d. As shown in Figure 5c,d, the impact toughness and flow rate (MFR) is shown in Figures5d and6d. As shown in Figure5c,d, the impact toughness and molecularmolecular fluidity fluidity of ABS of ABS with with different different additives additives did did not significantlysignificantly attenuate attenuate when when compared compared to to pure pureABS ABS(for (forthe theresults, results, see see Figure Figure S3) S3) after after aging aging by the convectionconvection oven, oven, indicating indicating that that the the resin resin itself itselfhad no had serious no serious cross-linking cross-linking phenomenon, phenomenon, and and the the addition of of the the antioxidant antioxidant had had no enoffect effect on on the impactthe impact strength strength and and melt melt flow flow rate. rate. Figure Figure 6c,d6c,d demonstrate that that the the ABS ABS undergoes undergoes considerable considerable cross-linking,cross-linking, which which shows shows an anevident evident decrease decrease in in melt melt flowflow rate.rate. The The ABS ABS sample sample with with GM GM increased increased its impactits impact strength strength and and melt melt flowflow raterate of of ABS, ABS, indicating indicating that the that bifunctional the bifunctional group in GMgroup can in prevent GM can preventthe the macromolecular macromolecular radical radical cross-linking cross-linking curing causedcuring bycaused less oxygen by less in oxygen repeated in extrusion. repeated extrusion.

Figure 5. Optical and mechanical properties versus aging cycles for ABS: (a) yellow index (YI); (b) color Figuredi ff5.erence Optical value and (∆ Emechanical); (c) notched properties impact strength; versus and aging (d) melt cycles flow for rate ABS: (MFR). (a) yellow index (YI); (b) color difference value (ΔE); (c) notched impact strength; and (d) melt flow rate (MFR).

PolymersPolymers 2019,2020 11, ,x12 FOR, 46 PEER REVIEW 8 of 108 of 10

Figure 6. Optical and mechanical properties versus repeated extrusion for ABS: (a) yellow index (YI); Figure(b) 6. color Optical difference and mechanical value (∆E); (cproperties) notched impact versus strength; repeated and extr (dusion) melt flowfor ABS: rate (MFR).(a) yellow index (YI); (b) color difference value (ΔE); (c) notched impact strength; and (d) melt flow rate (MFR). 4. Conclusions

4. ConclusionsIn summary, we successfully obtained high thermal stability and a better yellowing-resistant ABS with the GM additive in the convection oven or the extruder. In the oxygen convection oven environment,In summary, the we polybutadiene successfully double obtained bond high of the thermal ABS was stability attacked byand the a active better free yellowing-resistant radical to form ABS awith carbonyl the GM group. additive It can be in clearly the convection observed from oven the or FTIR the thatextruder. the carbonyl In the index oxygen value convection of ABS with oven environment,the GM is thethe lowest,polybutadiene which is much double smaller bond than of th thate ABS of ABS was with attacked DSPDP, by Irganox the active 1076 and free Irganox radical to form3114. a carbonyl As the numbergroup. It of can aging be cycles clearly increased, observed the fr thermalom the decompositionFTIR that the temperaturecarbonyl index (TGA) value of ABS of ABS withwith the GM wasis the higher lowest, than thatwhich of ABSis much with othersmalle additives.r than that These of results ABS with indicated DSPDP, that the Irganox difunctional 1076 and Irganoxstructure 3114. of As GM the could number reduce of the aging formation cycles of carbonyl increased, group the by thermal the reaction decomposition with free radicals temperature prior (TGA)to of aging ABS degradation. with GM was It also higher proved than that that the of acrylate ABS with structure other of additives. bisphenol monoacrylateThese results can indicated rapidly that capture macromolecular free radicals in the initial stage, generate relatively stable free radicals and the difunctional structure of GM could reduce the formation of by the reaction with terminate the reaction. In the extrusion environment with less oxygen, the lower yellow index and free radicals prior to aging degradation. It also proved that the acrylate structure of bisphenol smaller chromatic aberration demonstrated better color retention of ABS sample with GM. The higher monoacrylatemelt flow ratecan ofrapidly ABS sample capture with macromolecular GM also indicated free its radicals excellent in ability the initial to capture stage, macromolecular generate relatively stableradicals. free radicals It could and effectively terminate inhibit the thereaction. cross-linking In the ofextrusio polymers,n environment slow the aging with of materials less oxygen, and the lowerimprove yellow the index heat-aging and smaller resistance chromatic of ABS. aberration demonstrated better color retention of ABS sample with GM. The higher melt flow rate of ABS sample with GM also indicated its excellent ability Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4360/12/1/46/s1, to captureFigure S1:macromolecular Thermogravimetric radicals. analysis It (TGA) could results effect forively ABSwith inhibit different the additivescross-linking after di offferent polymers, extrusion slow the agingtimes: of (a )materials the first extrusion, and improve (b) the thirdthe heat-aging extrusion, (c )resistance the fifth extrusion, of ABS. (d ) the sixth extrusion; Figure S2: General scheme of thermal-oxidative degradation of ABS resin and its inhibition mechanism by GM, DSPDP, SupplementaryIrganox 1076, Materials: and Irganox The 3114; following Figure S3: (aare) Notched available impact online strength at ofwww.mdpi.com/xxx/s1, pure ABS aged by thermal Figure oven, S1: Thermogravimetric(b) Melt flow rate analysis of pure ABS(TGA) aged resu bylts thermal for ABS oven. with different additives after different extrusion times: (a) the firstAuthor extrusion, Contributions: (b) the Conceptualization,third extrusion, ( S.L.c) the and fifth Y.W.; extrusion, Methodology, (d)Y.W.; the Validation,sixth extrusion; Y.W.; Formal Figure Analysis, S2: General schemeG.W. of andthermal-oxidative Y.W.; Investigation, degradation Y.W.; Resources, of ABS S.L.; resin Writing—Original and its inhibition Draft Preparation,mechanism Y.W.;by GM, Writing—Review DSPDP, Irganox and Editing, Y.W., M.C., M.L. and Z.L.; Visualization, Y.W., M.C., M.L. and Z.L.; Supervision, S.L.; Project 1076,Administration, and Irganox 3114; S.L. Figure All authors S3: ( havea) Notched read and impact agreed strength to the published of pure versionABS aged of the by manuscript. thermal oven, (b) Melt flow rate of pure ABS aged by thermal oven. Funding: This research received no external funding. AuthorConflicts Contributions: of Interest: TheConceptualization, authors declare no S.L. conflict and of interest.Y.W.; Methodology, Y.W.; Validation, Y.W.; Formal Analysis, G.W. and Y.W.; Investigation, Y.W.; Resources, S.L.; Writing—Original Draft Preparation, Y.W.; Writing—Review and Editing, Y.W., M.C., M.L. and Z.L.; Visualization, Y.W., M.C., M.L. and Z.L.; Supervision, S.L.; Project Administration, S.L. All authors have read and agreed to the published version of the manuscript.

Funding: This research received no external funding.

Conflicts of Interest: The authors declare no conflict of interest.

Polymers 2020, 12, 46 9 of 10

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