cbe 4009 polymer processing –...

Chemical structure of a polymera) the nature of the repeating unitsb) the nature of the end groupsc) the composition of possible branches and cross-linksd) the nature of defects in the structural sequence

Fundamental characteristics of polymerschemical structure and molecular mass distribution pattern

~ determine all the properties of the polymer

Molecular mass distribution ~ average molecular size and its regularity~ may vary greatly depending on the method of synthesis

of the polymer

Polymer ~ a large molecule built up by the constitutional repeating units(structural units)

CBE 4009 Polymer Processing – Basic

Geometrical arrangements of the atoms in a polymer chainConfiguration: arrangements fixed by the chemical bonding

cannot be altered unless chemical bonds are broken or reformed

Examples: head to head, head to tail, tail to tail configuration in vinyl polymers stereoregular arrangement: cis- and trans-isomer,

1,2- and 1,4-addition, or d- and l-forms

Conformation: arrangements arising from rotation about single bonds

In dilute solutions the molecules are in continuous motion and assume different conformations in rapid succession(random coils)

In the solid state many polymers have typical conformations, such as folded chains and helical structures


C CR

HH

HC C

H

H

H

R

or C C

H

H

H

R

Head to Head, Head to Tail

-CH2-CH-CH2-CH-Cl Cl

-CH-CH2-CH2-CH-Cl Cl


C CHCH3

CH2 CH2

C CCH3

CH2

CH2

H

ciscis-isoprene

(natural rubber)

bulky groups on same side of chain

transtrans-isoprene (gutta percha)

bulky groups on opposite sides of chain

cis/trans Isomer


• Stereoisomerism


-CH2-C-R

CH=CH2

-CH2-CH-

RC=CH2

1,2-addition 1,4-addition

Substitutional isomer

EB

A

D

C C

D

A

BE

mirror plane

Optical isomer

Tacticity – stereoregularity of chain

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

C C

H

H

H

R

C C

H

H

H

R

C C

H

H

H

R R

H

H

H

CC

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

isotactic – all R groups on same side of chain

syndiotactic – R groups alternate sides

atactic – R groups random


Homopolymer ~ the structural units are identical Copolymer ~more kinds of basic units(e.g. two or three)

Alternating copolymer ~ considered as homopolymers with a composed structural unit

Random copolymer ~ obtained from two or more monomers which are present simultaneously in onepolymerization reactor

Graft copolymer ~ a homopolymer is prepared first and in a second step one or more monomers are

grafted onto this polymerthe final product consists of a polymeric backbone with side branches

Block copolymer ~ one monomer is polymerized, after which another monomer is polymerized on to the living ends of the polymeric chainsthe final product is a linear chain with a sequence of different segments


Copolymers

two or more monomers polymerized together

• random – A and B randomly vary in chain

• alternating – A and B alternate in polymer chain

• block – large blocks of A alternate with large blocks of B

• graft – chains of B grafted on to A backbone

A – B –

random

block

graft

alternating


Fig. A chronology of the discovery of polymers and their modification. [Courtesy of Prof. Hans G. Fritz of IKT Stuttgart, Stuttgart, Germany]


• Polymer Blends


Two Types of Plastics

1. Thermoplastics – Chemical structure remains unchanged during

heating and shaping – More important commercially, comprising more

than 70% of total plastics tonnage 2. Thermosets

– Undergo a curing process during heating and shaping, causing a permanent change (called cross‐linking) in molecular structure

– Once cured, they cannot be remelted

Amorphous Polymer ~ below Tg, like ordinary inorganic glasshardness, stiffness, brittleness, transparency

Crystalline Polymer ~ crystallize below Tm, geometrically regular structure, strong, tough, stiff,more resistant to solvents and chemicals

Glass Transition Temperature(Tg)~ the temperature beginning the segmental motion~ polymeric materials undergo a marked change in properties

associated with the virtual cessation of local molecular motion

Melting Temperature(Tm)~ the temperature of disappearance of the last traces of polymer

crystalline phase~ material becomes a viscous liquid with discontinuous changes

in density, refractive index, heat capacity, transparency and other properties

Melting vs. Glass Transition Temp.

What factors affect Tm and Tg?

• Both Tm and Tg increase with increasing chain stiffness

• Chain stiffness increased by1. Bulky side groups2. Polar groups or side

groups3. Double bonds or aromatic

chain groups

• Regularity (tacticity) – affects Tm only



Polymer Classification: Terminology

While we have chosen an applications perspective on polymer classification, many alternate schemes are widely used.

These are usually composition/property specific, as opposed to applications oriented.


Polymer Classification: Chemical Class

A popular classification scheme amongst chemists is based on polymer functionality.

Polyesters: poly(ethylene terephthalate) - Dacron

Polyamides: poly(caprolactam) - nylon 6

Urethanes: carbamate linkages through reaction

of diisocyanates and diols.

Another (!) classification scheme, again favored by chemists is based on differences between the polymer and constituent monomer(s). Condensation polymers: synthesis involves elimination of

some small molecule (H2O in the preparation of nylon) Addition polymer: formed without loss of a small molecule

i.e. ethylene polymerization to generate poly(ethylene)

C O

O

N C

OH

N C

O

O

H

Free radical polymerization (addition polymerization)

Initiator: example - benzoyl peroxide

C

H

H

O O C

H

H

C

H

H

O2

C C

H H

HHmonomer(ethylene)

R +

free radical

R C C

H

H

H

H

initiation

R C C

H

H

H

H

C C

H H

HH

+ R C C

H

H

H

H

C C

H H

H H

propagation

dimer

R= 2

Addition Polymerization


Condensation Polymerization

• Some of the original monomer’s materials are shed (condensed out) during polymerization process

• Process is conducted in the presence of a catalyst• Water, CO2 are commonly condensed out but other compounds can

be emitted including HCN or other acids

Water is “Condensed out” during polymerization of Nylon


엔지니어링 플라스틱은범용엔지니어링 플라스틱과 슈퍼엔지니어링 플라스틱으로 분류됨

범용엔지니어링 플라스틱 중 폴리아마이드(PA), 폴리아세탈(POM), 폴리카보네이트(PC), 폴리페닐렌옥사이드(M-PPO), 폴리부틸렌테레프탈레이크(PBT) 등 5가지 플라스틱을 5대 엔지니어링 플라스틱이라 부름

슈퍼엔지니어링 플라스틱에는 폴리이미드(PI), 폴리설폰(PSF), 폴리페닐렌설파이드(PPS), 폴리아마이드이미드(PAI), 폴리에테르설폰(PES), 폴리에테르에테르케톤(PEEK), 폴리에테르이미드(PEI), 액정폴리에스테르(LCP), 폴리에테르케톤(PEK) 등이 있음

엔지니어링 플라스틱(engineering plastics, EP)

□□ 구조용 및 기계부재에 적합한 고성능 플라스틱으로서 주로 금속 대체를 목표로 함□□ 자동차 부품이나, 기계부품, 전기, 전자부품과 같은 공업적 용도에 사용되는 플라스틱□□ 500 kgf/cm2(49MPa) 이상의 인장강도, 100 oC 이상의 내열성을 갖음

※내열성이 더욱 높아 150 oC 이상의 고온에서도 장기간 사용할 수 있는 것을 슈퍼엔지니어링 플라스틱(super engineering plastics)이라고 함


범용 엔지니어링 플라스틱의 특징

수지 장점 단점

결정성수지 NYLON 강인성, 내약품성내유성, 내마찰마모성

흡습시 치수변화성형시 치수안정성

POM 내피로성, 강성내마찰마모성

성형시 치수안정성난연화 곤란

PBT 내약품성, 내마모성전기적특성, 내열성

GF강화시 이방성성형시 치수안정성

비결정성수지 PC 내충격성, 투명성치수안정성

내약품성내 Stress Crack성

MPPO 성형성, 내충격성치수안정성, 내수성

내약품성내유성, 내열성



Additive Classification (첨가제 분류):It is relatively rare for an article to be made from polymer alone. Most are polymer compounds, consisting of a mixture of polymer and various additives. These include:


1) 가소제(plasticizer)non-volatile solvents added to improve flexibility

• 고분자 물질에 유동성을 주어 plastic flow를 유발시켜 가공을 쉽게 하고, 고분자의 딱딱한 정도를 감소시켜 유연성을 증가시킴(Tg를 낮춤)

• 첨가제 수요의 가장 큰 부분을 차지함

□□ 가소제의 요구조건① 고분자 물질과 잘 섞여서 균일한 상을 이루어야 함② 유리전이 온도가 낮아야 함③ 확산에 의해 고분자 밖으로 배출되지 않아야 함④ 가공시 휘발을 억제하기 위해 비점이 300 oC 이상이 되어야 함

Dialkyl phthalates in poly(vinylchloride), Dioctyl phthalate (DOP)□□ MW : 390, bp : 384 oC, mp : -50 oC, 용해도 지수(δ) : 7.9□□ 저렴하면서 가소성이 좋기 때문에 유연한 PVC를 제조하는데 널리 사용됨

※ Nylon, acryl계 고분자⇒물이 가소제

※가소제 첨가에 따른 기계적 물성유리전이온도(↓), 용융점(↓), 인장강도(↓), 탄성율 (↓), 연신율(↑), 충격강도 (↑)


2) Fillers: solid additives used to modify physical properties.

기계적 강도, 치수안정성, 열변형온도, 견고도 등의 물리적 성질을 증가시키거나, 수지의 가격을 낮추고, 가공성을 향상시키기 위하여 첨가하는 물질

① 충전제 (filler) : 기계적 강도를 크게 감소하지 않고 비용감소를 목적으로 하는경우② 강화제(reinforcement) : 기계적 성질(탄성율, 인장강도 등) 및 다른 물리적 성질의보강을 주 목적으로 하는 경우

사용 예• 흑연, 카본블랙, 금속류 등 : 성형수축을 감소시키거나 정전기를 최소화하기 위함• 카본블랙, 실리카 : 강도, 마모저항성 등과 같은 기계적 물성을 향상시키기 위함

Dilution - talcReinforcing - carbon black in tiresToughening - rubber in ABS plastic

※충전제와 고분자 matrix간의 계면접착은 좋은 충전 효과를 위하여 매우 중요함


※섬유강화수지(Fiber Reinforced Plastics, FRP)섬유를 보강재로 사용하여 강도를 향상시킨 수지□□ 밀도가 낮음□□ 비강도(specific strength)가 높음⇒응용분야 : fishing rods, tennis racket, skis, aircraftfiber로 사용하는 물질 : glass, graphite, boron, Kevla 등수지로 사용하는 물질 : 불포화폴리에스터, PBT, Nylon66, polycarbonate 등※복합재료(composite materials)FRP의 경우보다 섬유의 사용량을 60~70 %까지 증가시킴으로써 수지와섬유간의물성들이 복합적으로 결합되어 보다 개선된 물성을 갖도록 가공된 소재


3) Light Stabilizer (광안정제): prevent plastics from discoloration and degradation due to be exposed to sunshine and UV light

자외선 안정제• 자외선은 200~300 nm의 파장을 지닌 광선으로, 고분자 사슬의 공유결합을깨뜨리기에 충분하므로, 자유 라디칼 반응을 일으켜 고분자를 분해시킴• 이를 방지하기 위하여 자외선을 흡수하는 유기 화합물(benzophenone 등)이 사용됨⇒벤조페논은 UV 영역에서 높은 흡광계수를 가지며, 흡수된 방사 에너지를화학적인 변화없이 열로 전환시킴

4) Antioxidants(산화방지제 ): compounds that reduce polymer degradation through intervention in free radical reactions

• 성형공정이나 사용 중에 열 또는 다른 물리적 자극에 의하여 분해되어 생성된자유라디칼의 산화반응을 억제하기 위하여 사용되는 첨가제

5) 열 안정제열에 의한 분해반응을 억제하기 위하여 첨가되는 물질(납, barium, cadmium, 유기인 화합물 등이 사용됨)


6) Flame Retardant (난연제): keep safety from fire accident대부분의 고분자는 탈 때 많은 유해한 물질을 배출하므로 고분자에 난연성을부여하는 것이 요구됨(TV, 라디오, 카펫, 커튼 등)예) 유기 염화물, 유기 브로민 화합물, 유기 인산, 안티모니 산화물, 보론 화합물등

7) Compatibilizer (상용화제)• 계면접착력과 상용성을 향상시키기 위하여 첨가되는 물질• 많은 고분자들은 서로 불용성이기 떄문에 가공중에 상분리를 일으킴⇒ 이러한 불용성 블렌드는 분산상과 매트릭스 사이의 취약한 계면 결합력으로기계적 물성이 떨어짐

8)Antistatic agent(대전방지제): dust attraction free, discharge from damage the electronic chips and spark discharge from danger of fire and explosions

9) Lubricants(윤활제): beneficial effect on dispersion of filler, mold release property

10)Colorants: additives used to change product aestheticsPigments - soluble colorantsDyestuffs - insoluble additives

cbe 4009 polymer processing –...

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