Plasticizers External plasticizer: low MW. Liq. that help increase mobility of high MW entangled polymers - the plasticizer reduces the polymer-polymer chain 2 nd bonding softer, more easily deformable mass - performance – need plasticizer with low volatility MW solvent < MW plasticizer < < MW polymer
Internal plasticizer: making copolymer with soft polymer get desirable product property at a particular temp. (whereas external plasticizer—get desirable product at a wider range of temp.) Example of internal plasticizer
Ex. PVC: has lots of external plasticizer and additives ex. DOP (dioctyl phathalate) Unplasticized PVC -- rigid material used for pipes and fittings Plasticized PVC -- depend on level of plasticizer –leather-like upholstery –wire and cable covering –shower curtains –packaging film ex. Plastisols: 100 parts DOP phr + stabilizer + pigments low vis. suspension (~vis of plasticizer) melt film (flexible solid) suspension of PVC beads in plasticizer
Efficiency of plasticizer Select plasticizer with high solubility in & high compatibility to Polymer Matrix The more similar structure the higher solubility, compatibility Ex. -Plasticizers have to stay inside the matrix w/o migration or blooming Plasticizer: Schematic drawing of polymer dissolution
สารประสาน (Coupling Agents) สารประสานหรือสารช่วยยึด (coupling agents or adhesion promoters) -function as a bridge/binder between polymers and fillers by forming a strong interaction between the two phases How to use coupling agents: 1. coating/adjusting the surfaces of fillers & fibers first, then mix with polymers 2. Mix the coupling agent directly with polymer and filler during compounding process (sometimes called compatibilizer)
Examples of some silane coupling agents
ฟิลเลอร์ (Fillers) Filler: solid additives put into polymers to reduce cost (extenders) or improve mechanical properties of polymers (active fillers) - Examples of เอกซ์เทนเดอร์ (extenders) or inert fillers are CaCO3, talc, kaolin, wood dust - Examples of ฟังก์ชันแนลฟิลเลอร์ (functional fillers) or active fillers are reinforcing fillers –(reinforcing filler is functional filler to increase strength, especially tensile strength) Some polymers use large amount of fillers: PVC ( พอลิไวนิลคลอไรด์ ), rubber ( ยาง ) Some polymers use low amount of fillers: PE, PMMA
Selection of Fillers Depends on -price -properties of fillers -Required properties of products ex. For high tensile strength product, fillers need to be + hard/strong compared to polymer matrix + with high aspect ratio + disperse well in polymer matrices For high clarity, fillers need to + have similar refractive index as the polymer + Or need to be small in the nanometer range ( nanoparticles) For high quality surface, filler size has to be small and round, or platy For low moisture adsorption, filler needs to absorb low moisture and have strong interaction with polymer.
Shapes and aspect ratios of different types of fillers
แอนติออกซิแดนซ์ (Antioxidant) When polymers react with oxygen, they form peroxide bonds (O-O). These bonds easily break into free radical ( อนุมูลอิสระ ) and break the polymer chains. Oxidation Mechanism
Roles of Different Types of Antioxidants
Heat stabilizer ( สเตบิไลเซอร์ ) In the polymer processing process, polymers are exposed to high temperature. The degradation of polymer during processing leads to changes in the color of polymers. Heat stabilizer is added to polymers to avoid degradation during processing related to high temperature.
BOX 2.2:Thermal degradation of some commercial polymers
BOX 2.2:Thermal degradation of some commercial polymers (con’t)
Nucleating agent helps in forming polymer crystals quickly thus having small crystal size. (ref. Milliken®, SpecialChem S.A.) สารก่อผลึก (Nucleating Agent)
Appearance: Since light can pass through small crystals better than large crystals, nucleating agent thus - helps improve penetration of light through the polymer film and - improve clarity of the film. In the processing point of view: Small crystals shrinks in mold less than big crystals when cooled - plastic products can be removed from molds faster. - products maintain shape better when cooled