Melt Compounding of Rigid PVC Formulations with Hydrotalcites

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1 Melt Compounding of Rigid PVC Formulations with Hydrotalcites David Hitt, Barry Haworth & Noreen Thomas, Loughborough University Institute of Polymer Technology & Materials Engineering (IPTME)

2 PRESENTATION / CONTENT Introduction Materials Results & Discussion: (1) Dynamic & static thermal stability (2) Mechanical properties compression moulded (3) Mechanical properties extruded products (4) Characterisation Conclusions to-date

3 Acknowledgements: EPSRC award of the Research Grant: Reference: EP/D025354/1 Other VinylSUM colleagues at Loughborough University and industrybased Co-authors (David Hitt, Noreen Thomas) Mohammad Algahtani (MSc Project Student 2007) studies on OBS stabilised compounds. PVC / hydrotalcite research: - part of the EPSRC-sponsored VinylSUM initiative at Loughborough University).... SUM sustainable use of materials

4 Introduction Drivers for this project? nanocomposites sustainability Particulate additives advantages in PVC: Mechanical or functional performance; Processing behaviour & stability; Enhanced property-cost ratios.

dispersion of layered particles - greater specific surface area -

5 Nano-clay dispersion in thermoplastic nanocomposite structures: - intercalation & exfoliation (separation) and subsequent dispersion of layered particles - greater specific surface area - key to property enhancement, including stability and mechanical properties?

6 Hydrotalcites are forms of hydrated magnesium-aluminium-hydroxycarbonates - typical formula: Mg 6 Al 2 (OH) 16 CO 3 4H 2 O. LDH layered double hydroxides - layers of magnesium hydroxide and aluminium hydroxide with anionic interlayers comprising the carbonates and bound water. It is the capacity of hydrotalcites for anionic exchange that makes the materials highly suited to the task of stabilising PVC.

7 Basic Layer [Mg 1-x Al x (OH) 2 ] x+ How does hydrotalcite work with PVC? Mg 1-x Al x (OH) 2 Mg 1-x Al x (OH) 2 Inter Layers [(CO 3 ) x/g mh2o] x- H 2 O CO 3 H 2 O + 2HCl (in PVC) H 2 O Cl H 2 O Cl + CO 2 + H 2 O Mg 1-x Al x (OH) 2 Mg 1-x Al x (OH) 2 Basic Layer [Mg 1-x Al x (OH) 2 ] x+

8 Hydrotalcite co-stabilisation - relates to the capacity of the materials to react with / scavenge HCl formed during the degradation of PVC (1) the interlayer anions react with HCl (2) the hydroxide layers are lost as these react with HCl to form metal chlorides. Literature: Sensitivity to Mg/Al ratio Optimum addition level appears to be in the range 2phr (Ca/Zn) to 5phr (Sn or Pb, co-stabilised) Intercalated layer structures - enhanced stability & properties?

9 Sustainability source reduction achievable by nanocomposites: Enhanced performance - similar formulations; OR Retention of performance - less dependence on additives Product lifetime extension? Enhanced stability and physical properties (mechanical; barrier; plasticiser migration..)

10 Materials & Experimental PVC / hydrotalcite compounds Experimental methods - given in specific sections - full details in the conference paper

11 PVC compounds: compression moulding Component Supplier / Grade phr phr phr phr PVC K-68 Hydrotalcites Ca / Zn INEOS ChlorVinyls EVIPOL SH6830 Alcamizer P93 Sorbacid 911 Chemson PWX15840 (one pack) OBS Chemson PWX Sn Akcros BTS71 2.0

12 PVC compounds: extrusion Component phr phr phr phr phr phr phr phr phr phr Core formulation: PVC (100), Ca / Zn (4.5), process aid (1.0), TiO 2 (4.0) Impact modifier Alcamizer P Sorbacid Effects of: impact modifier level (0, 4, 7phr) for 5phr hydrotalcite hydrotalcite level (0, 2, 5, 10phr) for 7phr impact modifier Objective: achieve realistic properties on commercially-relevant formulations

13 Results & Discussion PVC compound & product stability (dynamic; static) Overview of mechanical properties (* Charpy impact in twin-screw extruded samples) Characterisation / analysis

14 1a Dynamic stability of PVC torque rheometry Dry blends - Haake Rheocord 90 Settings: temperature 190 C, rotor speed 60rpm, batch weight 60g. Measurements - three values were derived from the torque-time curves: time to the gelation peak - equilibrium torque (indication of melt viscosity) - "stability time Torque (Nm) rpm 70 rpm 60 rpm 50 rpm Temperature ( C) (onset time for degradation gelation time) Time (sec)

15 1a Dynamic stability of PVC effect of hydrotalcites TORQUE (Nm) CaZn OBS OBS + 2phr Sorbacid 911 OBS + 2phr Alcamizer P93 CaZn + 2phr Sorbacid 911 CaZn + 2phr Alcamizer P TEMPERATURE OF MIX ( C) Summary: TIME (minutes) Hydrotalcites very little effect on steady-state torque (viscosity) or mechanical heating. 0 Ca/Zn OBS Sn significant increase in stability (2phr, 5phr) increase in stability no clear trend (5phr)

16 1b Static stability of PVC oven at 190 C OBS Hydrotalcite Increased stability, relative to control OBS - top row

Sn - Hydrotalcite: Increased stability relative to control, but only for one grade of HT Sorbacid different mineral composition (reduced zinc) PVC 2008, Brighton UK.

17 Sn - Hydrotalcite: Increased stability relative to control, but only for one grade of HT Sorbacid different mineral composition (reduced zinc) PVC 2008, Brighton UK. 1b Static stability of PVC oven at 190 C Ca/Zn Hydrotalcite: Colour change improved stability with HT (2 phr); 5 phr shows reduced performance. Discoloration at 2 phr, agreement with dynamic stability data (HT increases stability).

18 2 Mechanical properties compression moulded Summary tensile properties: Overall, a retention in tensile yield strength, strength & elongation at break No clear effects, for different stabiliser types Reduced elongation for 5phr Sorbacid, in OBS stress (MPa) stress at break Yeild point Extension (mm) Break point Elongation at break 10phr Hydrotalcite (Ca/Zn): 11% reduction in yield stress, complemented by 15% increase in elongation potential for toughness enhancement?

2 Mechanical properties compression moulded energy at peak force at peak energy at failure Summary impact properties IFW1: 10mm, 10kg, 1-metre drop Force (N) deflection

19 2 Mechanical properties compression moulded energy at peak force at peak energy at failure Summary impact properties IFW1: 10mm, 10kg, 1-metre drop Force (N) deflection at peak deflection at failure Retention of ductile-mode failure Deflection (mm) Exceptions: Mixed-mode for 5phr HT (with OBS and Ca/Zn) Brittle-mode for 10phr HT (Ca/Zn)

20 3 Mechanical properties extruded PVC products Tensile properties: No significant changes retention of desirable properties. Charpy impact properties: Type A, notch tip radius of 0.25mm, BS EN ISO 179-1:2001. (80mm beam samples of 10mm width and 8mm ligament) Ray-Ran pendulum impact test, standard hammer (velocity 3.8 ms -1, potential energy of 7.5 J).

3 Mechanical properties extruded PVC products Significant enhancement of impact toughness (Ca/Zn modified), in combination with impact modifier

21 3 Mechanical properties extruded PVC products Significant enhancement of impact toughness (Ca/Zn modified), in combination with impact modifier co-modification Transition from brittle to ductile, as hydrotalcite addition increased Enhancements obtained for each grade of hydrotalcite, up to 10phr

22 180 Impact modifier constant Increasing Alcamizer Impact modifier constant Increasing Sorbacid REF 2A/7M 5A/7M 10A/7M CORE 5A/0M 5A/4M 5A/7M REF 2S/7M 5S/7M 10S/7M IMPACT STRENGTH (kj/m 2 ) Alcamizer constant Increasing modifier

4 Characterisation TEM analysis REF 2A/7M

phr hydrotalcite particles have a high aspect

effective distribution around PVC primary

23 4 Characterisation TEM analysis REF 2A/7M 5A/7M 10A/7M Increased HT concentration: 0-10 phr hydrotalcite particles have a high aspect ratio / well dispersed acrylate modifier effective distribution around PVC primary particles TiO 2 see REF sample (left side) Hydrotalcite (fine particles / well dispersed) produces the significant enhancement in impact strength.

24 Conclusions Hydrotalcites are effective co-stabilisers for rigid PVC compounds; enhanced static and dynamic stability has been achieved (Sn, OBS, Ca/Zn primary stabilisers). Some sensitivity to HT concentration and grade has been observed effects are related to the capacity for anionic exchange in the interlayer structure, when PVC degradation is initiated. For compression moulded samples (co-stabilisers with Ca/Zn and OBS stabilisers), hydrotalcite additive levels of around 2phr are optimal. At this level, no detrimental effects on mechanical performance are observed. In Ca/Zn-stabilised extrusion formulations, hydrotalcites (at 2-3phr) can induce impact toughness enhancement, in combination with an elastomeric impact modifier.

25 Future Perspectives: towards property enhancement Commercial hydrotalcites (700 nm typically): technical interpretations; other extruded formulations (OBS) Ongoing research synthesised hydrotalcite formation, aimed at reducing particle size towards the nanometre scale ; Exploitation of stability / mechanical property relationships due to increased specific surface area of particulate additives.

26 Thank you for your attention!

27 IMPACT TEST RESULTS Former standard (BS7413): 50mm Charpy with notch tip radius ~ 0.11mm Extrudates with AP93 (phr) REF 2A/7M 5A/7M 10A/7M Breaks Non breaks Average KJ/m Standard deviation At 2phr two distinct groups (1.86) (4.63)

The Potential of Silane Coated Calcium Carbonate on Mechanical Properties of Rigid PVC Composites for Pipe Manufacturing

Materials Sciences and Applications, 2011, 2, 481-485 doi:10.4236/msa.2011.25065 Published Online May 2011 (http://www.scirp.org/journal/msa) 481 The Potential of Silane Coated Calcium Carbonate on Mechanical