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Preparation and Research on Properties of Modified Pla and Its Foam Materials

Author: MuZhengYang
Tutor: ZouJun
School: Jiangsu University of Science and Technology
Course: Materials Science
Keywords: Polylactic acid Dibenzoyl peroxide Increasing-viscosity modification ADR Chain extension and branching modification Foaming materials
CLC: TQ328
Type: Master's thesis
Year: 2013
Downloads: 4
Quote: 0
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Abstract

Application cost of PLA is high, toughness is poor, the quantity of branched chains isless, its poor processing stability is subject to bring about the breakage of molecular chain,and melt viscosity and strength are poor, those go against foam forming.The increasing viscosity modified poly(lacticacid)/poly(butylene succinate)(PLA/PBS)composite materials with benzoyl peroxide (BPO) were prepared by melt blending, and therheological properties, gel fraction, thermal properties, crystallization property, mechanicalproperties and thermodynamic performance were investigated firstly. With the increase oftorque of blends, melt apparent viscosity and non-newtonian index, the declining amplitudeof melt appeard viscosity decreased with the increasing shearing rate. In addition, the gelfraction of blends increased. Polarized optical microscopy and differential scanningcalorimetry indicated that the crystallization capacity of PLA weakened, degree ofcrystallinity and melting point droped off with the increase of BPO content. Mechanicalproperty studies and scanning electron microscope manifested that impact strength, tensilestrength, elongation at break and Young modulus all enhanced, materials presented thetransition from brittleness to toughness remarkably, the compatibility between PLA and PBSwas improved, the dispersive PBS phase improved the toughness of materials effectivelywith the increase of BPO content. Elongation at break increased remarkably, the range ofyield of matrix on the impact fracture surface aggrandized and stress whiteningphenomenon became more obvious with the increase of PBS content. Dynamic thermalmechanical analysis demonstrated that storage modulus increased and internal frictionminished with the increase of BPO content. The storage modulus of blends exceeded purePLA and the internal friction was minimum while BPO content was1.0phr.The foaming materials were prepared by foaming experiments using PLA/PBS/BPOcomposite materials as base materials secondly. The effects of foaming agent and bubblenucleator on foaming properties and the thermodynamic performance of foaming materialswere investigated. The apparent density firstly decreased and then increasd, however, celldensity suited for opposite law, cell size and distribution were liable to be pyknotic andhomogeneous, then bubbles collapsed and merged, and cell size and distribution becameheterogeneous with the increase of foaming agent A content. Apparent density was lowerwhen the foaming agent A content was3or4phr. The effect of kind of foaming agent onfoaming properties was great, the foaming effect of foaming agent A was superior to foaming agent B in this experiment. Cell density firstly increasd and then reduced, celldiameter was small and mean at first, then cell size and distribution became heterogeneouswith the increase of nano-silica bubble nucleator content. Cell density was maximum whennano-silica bubble nucleator content was3phr. The effect of kind of bubble nucleator onfoaming properties was also great, the foaming effect of nano-silica was inferior to9900mesh Talc. Glass transition temperature and mechanical loss factor were hardly influencedby the addition of bubbles, the storage modulus reduced obviously with the decrease offoaming materials density. The storage modulus increased, the mechanical loss factordecreased below Tgand increased above Tgin glass transition region with the increase offrequency.The chain extension and branching modified PLA with ADR was prepared by reactiveblending, and molecular structural characteristics, rheological properties, gel fraction andthermodynamic performance were investigated finally. Then modified PLA foamingmaterials were prepared and the effects of ADR content on foaming properties of modifiedPLA were investigated. The torque of modified PLA increased, melt flow index fell off, andgel fraction went up with the increase of ADR content. SEC-MALLS-RI hyphenatedtechnique showed that molecular weight of modified PLA firstly increasd and thendecreased, molecular weight distribution firstly broadened and then narrowed down,branching factor reduced with the increase of ADR content. The molecular chainconformation of pure PLA was stretched shape, molecular chain conformation turned intorandom clew with the addition of ADR, and molecular chain curled into compact spherefrom random clew with sequential increase of ADR content. The conformational parameterswas minimum when ADR content was0.9phr. Dynamic thermal mechanical analysisindicated that the storage modulus of modified PLA increased and mechanical loss factorwas hardly influenced with the increase of ADR content. Foaming experiments researchshowed that cell density and expansion ratio all increased, and cell size and distributionwere inclined to pyknotic and homogeneous with the increase of ADR content. The celldensity was maximum when ADR content was0.9phr. Cell size and distribution becameheterogeneous, and the bubbles collapsed and merged along with sequential increase ofADR content.

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