Cellulose Technology Research

1 Colloidal Microcrystalline Celluloses O. A. BATTISTA

Downloaded by GEORGETOWN UNIV on June 27, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0010.ch001

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The science and technology o f polymers during the past few decades have been centered l a r g e l y around the phenomena and the products t h a t r e s u l t from p r e c i p i t a t i n g or " f r e e z i n g " long chain molecules i n t o f i x e d matrices l e a d i n g to important commercial s t r u c t u r a l shapes such as f i b e r s , f i l m s , p l a s t i c s , and c o a t i n g s . The b a s i c hypothesis around which the science o f microcrystalline c o l l o i d a l polymer chemistry (1) is u n f o l d i n g n e c e s s i t a t e s t h a t s p e c i f i c r e q u i s i t e s must be met; it is i n the d e l i b e r a t e combination o f these r e q u i s i t e s t h a t it d e r i v e s its value and originality. Firstly, the molecular weight o f the i n d i v i d u a l long-chain molecules must be high enough; the chain molecules must be long enough t o crystallize out o f s o l u t i o n or from a melt i n t o a two-phase network s t r u c t u r e comprising regions o f high l a t e r a l order (or crystallinity) and regions o f low lateral order (or low crystallinity). Secondly, a pretreatment must be i n v o l v e d which is capable of unhinging or loosening the i n d i v i d u a l m i c r o c r y s t a l s w i t h i n t h e i r precursor matrix without e x c e s s i v e l y s w e l l i n g them or d e s t r o y i n g t h e i r "crystallinity." Thirdly, once the i n d i v i d u a l m i c r o c r y s t a l s have been p r o p e r l y unhinged or loosened w i t h i n the polymer matrix, they must next be f r e e d by the proper k i n d o f mechanical energy. The i n d i v i d u a l microc r y s t a l s , comprising as they do hundreds of long-chain molecules aggregated together, will now act as d i s c r e t e , independent, submicron colloidal particles. C o l l o i d a l m i c r o c r y s t a l l i n e c e l l u l o s e s were the first o f a f a m i l y o f new products t h a t have emerged in recent years (Table 1 ) . The s i z e and shape o f n a t u r a l c e l l u l o s e m i c r o c r y s t a l s are more or l e s s f i x e d by n a t u r e . But wide v a r i a t i o n s in the dimension of such p a r t i c l e s are p o s s i b l e by the appropriate choice o f the n a t u r a l or s y n t h e t i c precursor raw m a t e r i a l (2,3,4). F i g u r e s 1 and 2 are e l e c t r o n micrographs illustrating the 1 In Cellulose Technology Research; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

CELLULOSE TECHNOLOGY

Table 1


Nine Members o f the M i c r o c r y s t a l Polymer Products Family.

1·

AVICELS

FROM CELLULOSES

2.

AVIAMXLOSES.

3.

AVIBESTS

4.

AVITENES

5.

AVTAMIDES

FROM NYLONS

6.

AVIESTERS

FROM POLYESTERS

7.

AVIOLEFINS..

8.

AVISILKS

FROM NATURAL SILKS

9.

AVIWOOLS

FROM NATURAL WOOLS

....FROM AMYLOSES FROM CHRYSOTILES ...FROM COLLAGENS

...FROM POLYPROPYLENES

In Cellulose Technology Research; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

RESEARCH


1. BATTiSTA

Colloidal Microcrystalline Cellulose

Figure 1.

Microcrystals from wood pulp alpha cellulose

Figure 2.

Microcrystals from rayon tire cord


3


4

CELLULOSE TECHNOLOGY RESEARCH

wide spread i n the lengths o f c e l l u l o s e m i c r o c r y s t a l s t h a t i s p o s s i b l e ; m i c r o c r y s t a l s o f wood c e l l u l o s e are compared with m i c r o - c r y s t a l s from v i s c o s e rayon a t the same m a g n i f i c a t i o n . C e l l u l o s e i s h i g h l y c r y s t a l l i n e , uniquely i s o t a c t i c l i n e a r polymer. I t contains m i c r o c r y s t a l s hinged together by t r u e (covalent) molecular bonds. Mechanical beating o f c e l l u l o s e f i b e r s leads only t o a separation o f the f i b r i l s , b u t mechanical energy alone cannot break the 1 , 4 ^ - g l y c o s i d i c bonds i n the molecular chains going from one c r y s t a l l i t e t o the other w i t h i n the f i b r i l with any degree o f e f f e c t i v e n e s s . However, once these hinges i n the i n t e r c o n n e c t i n g areas are broken, i n the case o f c e l l u l o s e by the use o f the hydronium i o n (HC1), then mechanical energy can be used t o cause the i n d i v i d u a l unhinged m i c r o c r y s t a l s t o d i s p e r s e i n t o a l i q u i d medium as i n d i v i d u a l c o l l o i d a l p a r t i c l e s . Not u n t i l a s u f f i c i e n t l y l a r g e number o f m i c r o c r y s t a l s i s so f r e e d does a mechanical g e l network develop t o g i v e a smooth, l a r d - l i k e g e l . F i g u r e 3 i l l u s t r a t e s t h e nature o f such aqueous suspensoids f o r m i c r o c r y s t a l l i n e c e l l u l o s e and f o r f i v e other members o f the m i c r o c r y s t a l l i n e polymer family. The m i c r o c r y s t a l s o f pure c e l l u l o s e i n aqueous g e l s do not melt, o f course. T h i s g i v e s such suspensoids a unique f u n c t i o n a l property which makes p o s s i b l e the development o f a new f a m i l y o f convenience foods; m i c r o c r y s t a l l i n e c e l l u l o s e g e l s are used i n precooked cans o f tuna f i s h , ham, chicken, turkey, and even potato salads as h e a t - i n s e n s i t i v e s a l a d d r e s s i n g s . No p r e v i o u s l y known e d i b l e salad d r e s s i n g formulation could stand up under the severe s t e r i l i z a t i o n requirements f o r such canned foods (Figure 4 ) · Table 2 l i s t s the f u n c t i o n a l c o n t r i b u t i o n s o f microc r y s t a l l i n e c e l l u l o s e s i n various product uses. F i g u r e 5 i l l u s t r a t e s the mechanism whereby d r y c o l l o i d a l p a r t i c l e s o f c r y s t a l l i n e c e l l u l o s e , containing numerous " h o l e s " v a r y i n g from 10 A-100 A i n diameter, may be produced· T h i s new porous form o f h i g h l y c r y s t a l l i n e c e l l u l o s e i n powder form i s capable o f absorbing o i l s , greases, c a t a l y s t s , e t c . When a d i l u t e s l u r r y o f a suspension o f i n d i v i d u a l m i c r o c r y s t a l s and l a r g e aggregates o f unhinged m i c r o c r y s t a l s i s spray-dried under proper c o n d i t i o n s , the f r e e m i c r o c r y s t a l s reagglomerate i n t o man-made c l u s t e r s not u n l i k e the manner i n which wooden matchs t i c k s aggregate when p i l e d on a t a b l e top. S t i l l other f a s c i n a t i n g o p p o r t u n i t i e s present themselves when chemistry i s wedded t o these novel c o l l o i d a l macromolecular p a r t i c l e s . F o r example, r e a c t i o n o f the m i c r o c r y s t a l l i n e c e l l u l o s e c r y s t a l s proceeds with p a r t i c u l a r ease and speed. D e r i v a t i v e s can be formed which are a l s o c o l l o i d a l . These are e n t i r e l y new m a t e r i a l s with very d i f f e r e n t p r o p e r t i e s and p o t e n t i a l a p p l i c a t i o n s . A t high degrees o f s u b s t i t u t i o n (D.S.), d e r i v a t i v e s o f m i c r o c r y s t a l l i n e c e l l u l o s e are s u b s t a n t i a l l y the same m a t e r i a l as produced from conventional c e l l u l o s e . A t low



1. BATTiSTA

Figure 3.

Colloidal Microcrystalline

Cellulose

Aqueous suspensoids of six classes of microcrystal polymer products

Figure 4. Typical commercial food products containing microcrystalline cellulose


5


6

Table 2 Puntional P r o p e r t i e s

and End Uses


of M i c r o c r y s t a l l i n e C e l l u l o s e s

Functionality

Product Uses

Emulsion S t a b i l i t y a t High Temperatures

Heat S t a b l e Dressings

Ice-Crystal

Control

S t a b i l i t y To E f f e c t s o f Heat Shock

Frozen Desserts

Improved Body and Texture

Foam S t a b i l i t y Freeze/Thaw

Stability

Whipped Toppings

Improved Body and Texture

G e l l i n g Agent

Low C a l o r i e Dressings

Thickener

Sauces and Gravies

Suspending Agent

Suspension o f Food S o l i d s

Non-Nutritive F i l l e r

Confections Baked Goods



1. BATTiSTA

Figure 5.

Colloidal Microcrystalline Cellulose

Reaggregated cellulose microcrystals as porous colloidal particles



8


degrees o f s u b s t i t u t i o n , where the c o l l o i d a l nature o f the m i c r o c r y s t a l s i s maintained, the d e r i v a t i v e s form unique c o l l o i d a l d i s p e r s i o n s . Dispersions o f a t l e a s t 20% s o l i d s i n water can be produced. These may have the appearance o f greases, ointments, or l o t i o n s , depending on the extent o f topochemical d e r i v a t i z a t i o n and the nature o f the groups added. We have described m i c r o c r y s t a l l i n e c e l l u l o s e s , t h i s f i r s t i n a new species o f c o l l o i d a l m i c r o c r y s t a l polymer products t o reach world-wide commercial success. The knowledge gleaned from converting f i b r o u s c e l l u l o s e s i n t o new, u s e f u l c o l l o i d a l forms has guided us i n t o converting other l i n e a r and c r y s t a l l i n polymer precursors i n t o u s e f u l c o l l o i d a l forms. To date these have i n c l u d e d : c o l l o i d a l m i c r o c r y s t a l l i n e amyloses, microc r y s t a l l i n e mineral s i l i c a t e s , m i c r o c r y s t a l l i n e c o l l a g e n s , m i c r o c r y s t a l l i n e polyamides, m i c r o c r y s t a l l i n e p o l y s t e r s , m i c r o c r y s t a l l i n e polypropylenés, m i c r o c r y s t a l l i n e s i l k s , and m i c r o c r y s t a l l i n e wools. A t r e a t i s e encompassing the r e s u l t s o f our research i n the newest f i e l d s o f M i c r o c r y s t a l Polymer Science i n c o l l a b o r a t i o n with many a s s o c i a t e s over a p e r i o d o f 20 years now i s a v a i l a b l e ( 1 ) . T h i s author p r e d i c t s t h a t numerous new avenues o f opportunity remain unexplored f o r the more r e c e n t members o f the m i c r o c r y s t a l polymer science f a m i l y .

Literature Cited

1.

B a t t i s t a , O.A., M i c r o c r y s t a l Polymer Science, A T r e a t i s e . McGraw-Hill Book Co., Inc. 1975.

2.

B a t t i s t a , O. Α., and Smith, P.Α., Ind. Eng. Chem. (1962) 54, (9), 20-29.

3.

B a t t i s t a , O.A., e t al, Ind. Eng. Chem., (1956) 48 333-335.

4.

B a t t i s t a , O.A., and Smith, P.A., U.S. Patent No. 2,978,446 ( L e v e l - o f f D.P. C e l l u l o s e Products), 1961, April 4.


Cellulose Technology Research

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