Multihollow Polyester Particles as opacifying additive. Tânia M.T. Carvalho, Jorge Martins, Luísa Carvalho, Fernão D. Magalhães

Transcription

1 Multihollow Polyester Particles as opacifying additive Tânia M.T. Carvalho, Jorge Martins, Luísa Carvalho, Fernão D. Magalhães

2 Introduction Titanium dioxide is an extremely effective pigment for conferring opacity to thermoplastic materials. However, its high cost has driven the search for more economic alternatives, capable of being used as partial substitute for titanium dioxide in a masterbatch formulation. The use of hollow particles is an interesting approach. 2

3 Introduction Multihollow Polyester Particles (MHP) crosslinked polyester/styrene particles with numerous inner spherical voids separated by thin walls of polymer synthesized on a water/oil/water double emulsion system 3

4 Multihollow Particles The organic phase is dispersed in aqueous medium and retains in its interior numerous water droplets. After cross-linking the organic phase, solid, waterdispersed polymer particles containing alveoli of less than 1 µm in diameter are obtained. The difference between the refractive indexes of the polymer and the air in the alveoli causes light to scatter and creates an opacifying effect. During drying, water evaporates from the interior of the particles, forming internal voids. 4

5 Multihollow Particles Synthesis The unsaturated polyester styrene mixture is first neutralized with an amine (DETA) w After adding all organic phase, stirring was maintained for a predefined dispersion time. The double emulsion is diluted in water Polyester-styrene + DETA Water droplets Emulsion W/O Water + PVA Then, it is directly emulsified in the aqueous solution of a protective colloid (PVA) in a jacketed glass reactor under mechanical agitation The curing system (cumene hydroperoxide and ferrous sulphate) were added to the reactor 5

6 MVP incorporation in LDPE Dried particles Twin-screw micro-compounder + micro-injection moulder T fusion =120 ºC Vacuum oven: T=65 C P=0,2 bar Mix time= 5 min Screw velocity= 300 rpm Incorporations: 0,9 wt%, 1,8 wt%, 2,8 wt%, 3,7 wt%, 4,7 wt% LDPE T injection =145 ºC P=12 bar LDPE LDPE + 2,5 wt% 6

7 MVP characterization Beckman Coulter Counter Universal testing machine Scanning Electron Microscope VIS Spectrophotometer UV/VIS Spectrophotometer 7

8 Particle Size Distribution MVP characterization The particle size distribution the MHPs dispersions was measured on a Beckman Coulter (LS230 laser diffraction). The particle size distributions were computed by the equipment s software, based on Mie theory for light scattering. All cured dispersions were previously diluted and sonicated for 15 min, to avoid the formation of agglomerates. 8

9 MVP characterization Scanning Electron Microscopy (SEM) Particle morphology and internal vesiculation were observed using a Quanta 400FEG ESEM / EDAX Genesis X4M equipment. Thick MHPs films were applied on 2 cm glass slabs, dried for 2 h and then fractured in liquid nitrogen. This resulted in fracture a fraction of the MHPs present, allowing for observation of the internal vesiculation structure. The samples were sputtered with gold before being analyzed by SEM. 9

10 MVP characterization The tensile tests were performed on the Tinius Olsen H50KT equipment, equipped with a 10 kn load cell. All tests were carried out at room temperature and data processed by the Tinius Olsen Horizon application. Tensile Strength Test The sample is deformed until its fracture, at a fixed displacement speed (0.5 mm/s). Samples with t-bone shape were used having the nominal dimensions 80 x 11 x 2 mm 3. 10

11 MVP characterization Colour and Opacity Colourimetry The color and opacity were measured using a Konica Minolta CM-2500c colorimeter. The color quantification is evaluated according to the colorimetric model L* a* b* (CIELab). Opacity is determined by the difference in the coulor measurement of the sample on a contrast chart over white and black. UV/VIS Spectroscopy The absorption of radiation from electromagnetic in the visible and ultraviolet regions is measured. The transmittance of the samples is measured at wavelengths from 250 nm to 800 nm using a PerkinElmer LAMBDA 750 UV/Vis/NIR spectrophotometer. 11

12 Volume (%) Results Particle Size Distribution Speed (time) of the mechanical agitation Addition: 850 rpm ( 20 min) Dispersion: 1100 rpm (60 min) Cure: 300 rpm (120 min) Average particle size 5,21 µm Particle Size (µm) 12

13 Results SEM image of MHP (magnification 2150x)) SEM image of MHP (magnification 4200x)) 13

14 Results SEM image of MHP film fractured in liquid nitrogen (magnification 4200x) 14

15 Results Ultimate strength decreased slightly with the increase of %(MHP) incorporated in the polyethylene. The yield stress (elastic domain) is independent of the %(MHP) incorporated. Low adherence of the MHP to LDPE 15

16 Results SEM image of MHP after fracture (magnification 660x)) SEM image of MHP after fracture (magnification 2600x) 16

17 Results 1. Polyethylene 2. Polyethylene + 2% MHP 3. Polyethylene + 2% TiO 2 4. Polyethylene + 2% Lithopone 5. Polyethylene + 2% Inbond

18 Results The type of particles incorporated in the polyethylene does not change significantly the performance of the samples in tensile tests. 18

19 Results As expected, opacity increases with increasing percentage of MHP incorporated in polyethylene. 19

20 Results The opacity of the MHP is about 20% lower than that of titanium dioxide 20

21 Results Each of the samples is placed on a black standard and on a white standard, which also allows us to obtain information about their opacity E = L 2 + a 2 + b 2 21

22 Final Remarks Multihollow Polyester Particles (MHPs) were successfully synthesized. Sufficiently high stirring rate during the dispersion of polyester droplets in water is essential to guarantee good vesiculation. It is feasible to use MHPs as a partial substitute of titanium dioxide in masterbatch for white polyethylene, with adequate opacity. The type or %(m/m) of particles incorporated does not change significantly the performance of the samples in tensile tests. 22

23 Acknowledgments This work is funded by Projects: MasterOPAK (SI I&DT Projects in co-promotion) in the scope of Portugal 2020, cofunded by FEDER (Fundo Europeu de Desenvolvimento Regional) under the framework of POCI (Programa Operacional Competitividade e Internacionalização) Project UID/EQU/00511/2013-LEPABE, by the FCT/MEC with national funds and when applicable co-funded by FEDER in the scope of the Portugal 2020 Partnership Agreement. 23

24 Thank you for your attention Porto, PORTUGAL